Python next

Release date: XXXX-XX-XX

Core and Builtins

  • bpo-45494: Fix parser crash when reporting errors involving invalid continuation characters. Patch by Pablo Galindo.

  • bpo-45408: Fix a crash in the parser when reporting tokenizer errors that occur at the same time unclosed parentheses are detected. Patch by Pablo Galindo.

  • bpo-45385: Fix reference leak from descr_check. Patch by Dong-hee Na.

  • bpo-45167: Fix deepcopying of types.GenericAlias objects.

  • bpo-44219: Release the GIL while performing isatty system calls on arbitrary file descriptors. In particular, this affects os.isatty(), os.device_encoding() and io.TextIOWrapper. By extension, in text mode is also affected. This change solves a deadlock in os.isatty(). Patch by Vincent Michel in bpo-44219.

  • bpo-44050: Extensions that indicate they use global state (by setting m_size to -1) can again be used in multiple interpreters. This reverts to behavior of Python 3.8.

  • bpo-45121: Fix issue where Protocol.__init__ raises RecursionError when it's called directly or via super(). Patch provided by Yurii Karabas.

  • bpo-45083: When the interpreter renders an exception, its name now has a complete qualname. Previously only the class name was concatenated to the module name, which sometimes resulted in an incorrect full name being displayed.

    (This issue impacted only the C code exception rendering, the traceback module was using qualname already).

  • bpo-45056: Compiler now removes trailing unused constants from co_consts.


  • bpo-45515: Add references to zoneinfo in the datetime documentation, mostly replacing outdated references to Change by Paul Ganssle.

  • bpo-45475: Reverted optimization of iterating gzip.GzipFile, bz2.BZ2File, and lzma.LZMAFile (see bpo-43787) because it caused regression when user iterate them without having reference of them. Patch by Inada Naoki.

  • bpo-45428: Fix a regression in py_compile when reading filenames from standard input.

  • bpo-45467: Fix incremental decoder and stream reader in the "raw-unicode-escape" codec. Previously they failed if the escape sequence was split.

  • bpo-45461: Fix incremental decoder and stream reader in the "unicode-escape" codec. Previously they failed if the escape sequence was split.

  • bpo-45239: Fixed email.utils.parsedate_tz() crashing with UnboundLocalError on certain invalid input instead of returning None. Patch by Ben Hoyt.

  • bpo-45249: Fix the behaviour of traceback.print_exc() when displaying the caret when the end_offset in the exception is set to 0. Patch by Pablo Galindo

  • bpo-45416: Fix use of asyncio.Condition with explicit asyncio.Lock objects, which was a regression due to removal of explicit loop arguments. Patch by Joongi Kim.

  • bpo-45419: Correct interfaces on DegenerateFiles.Path.

  • bpo-45262: Prevent use-after-free in asyncio. Make sure the cached running loop holder gets cleared on dealloc to prevent use-after-free in get_running_loop

  • bpo-45386: Make xmlrpc.client more robust to C runtimes where the underlying C strftime function results in a ValueError when testing for year formatting options.

  • bpo-45371: Fix clang rpath issue in distutils. The UnixCCompiler now uses correct clang option to add a runtime library directory (rpath) to a shared library.

  • bpo-20028: Improve error message of csv.Dialect when initializing. Patch by Vajrasky Kok and Dong-hee Na.

  • bpo-45343: Update bundled pip to 21.2.4 and setuptools to 58.1.0

  • bpo-45329: Fix freed memory access in pyexpat.xmlparser when building it with an installed expat library <= 2.2.0.

  • bpo-41710: On Unix, if the sem_clockwait() function is available in the C library (glibc 2.30 and newer), the threading.Lock.acquire() method now uses the monotonic clock (time.CLOCK_MONOTONIC) for the timeout, rather than using the system clock (time.CLOCK_REALTIME), to not be affected by system clock changes. Patch by Victor Stinner.

  • bpo-45328: Fixed http.client.HTTPConnection to work properly in OSs that don't support the TCP_NODELAY socket option.

  • bpo-1596321: Fix the threading._shutdown() function when the threading module was imported first from a thread different than the main thread: no longer log an error at Python exit.

  • bpo-45274: Fix a race condition in the Thread.join() method of the threading module. If the function is interrupted by a signal and the signal handler raises an exception, make sure that the thread remains in a consistent state to prevent a deadlock. Patch by Victor Stinner.

  • bpo-45238: Fix unittest.IsolatedAsyncioTestCase.debug(): it runs now asynchronous methods and callbacks.

  • bpo-36674: unittest.TestCase.debug() raises now a unittest.SkipTest if the class or the test method are decorated with the skipping decorator.

  • bpo-45235: Fix an issue where argparse would not preserve values in a provided namespace when using a subparser with defaults.

  • bpo-45183: Have zipimport.zipimporter.find_spec() not raise an exception when the underlying zip file has been deleted and the internal cache has been reset via invalidate_cache().

  • bpo-45234: Fixed a regression in copyfile(), copy(), copy2() raising FileNotFoundError when source is a directory, which should raise IsADirectoryError

  • bpo-45228: Fix stack buffer overflow in parsing J1939 network address.

  • bpo-45192: Fix the tempfile._infer_return_type function so that the dir argument of the tempfile functions accepts an object implementing the os.PathLike protocol.

    Patch by Kyungmin Lee.

  • bpo-42135: Fix typo: importlib.find_loader is really slated for removal in Python 3.12 not 3.10, like the others in GH-25169.

    Patch by Hugo van Kemenade.

  • bpo-35474: Calling mimetypes.guess_all_extensions() with strict=False no longer affects the result of the following call with strict=True. Also, mutating the returned list no longer affects the global state.

  • bpo-45166: typing.get_type_hints() now works with Final wrapped in ForwardRef.

  • bpo-20499: Improve the speed and accuracy of statistics.pvariance().

  • bpo-24444: Fixed an error raised in argparse help display when help for an option is set to 1+ blank spaces or when choices arg is an empty container.

  • bpo-45021: Fix a potential deadlock at shutdown of forked children when using concurrent.futures module

  • bpo-39039: raises ReadError when a zlib error occurs during file extraction.

  • bpo-44594: Fix an edge case of ExitStack and AsyncExitStack exception chaining. They will now match with block behavior when __context__ is explicitly set to None when the exception is in flight.


  • bpo-45464: Mention in the documentation of Built-in Exceptions that inheriting from multiple exception types in a single subclass is not recommended due to possible memory layout incompatibility.

  • bpo-45449: Add note about PEP 585 in

  • bpo-20692: Add Programming FAQ entry explaining that int literal attribute access requires either a space after or parentheses around the literal.

  • bpo-45216: Remove extra documentation listing methods in difflib. It was rendering twice in pydoc and was outdated in some places.

  • bpo-45024: documentation has been expanded to explicitly cover how instance and subclass checks work, with additional doctest examples and an exhaustive list of ABCs which test membership purely by presence of the right special methods. Patch by Raymond Hettinger.


  • bpo-39679: Add more test cases for @functools.singledispatchmethod when combined with @classmethod or @staticmethod.

  • bpo-45400: Fix test_name_error_suggestions_do_not_trigger_for_too_many_locals() of test_exceptions if a directory name contains "a1" (like "Python-3.11.0a1"): use a stricter regular expression. Patch by Victor Stinner.

  • bpo-40173: Fix

  • bpo-45280: Add a test case for empty typing.NamedTuple.

  • bpo-45269: Cover case when invalid markers type is supplied to c_make_encoder.

  • bpo-45128: Fix test_multiprocessing_fork failure due to test_logging and sys.modules manipulation.

  • bpo-45209: Fix UserWarning: resource_tracker warning in _test_multiprocessing._TestSharedMemory.test_shared_memory_cleaned_after_process_termination

  • bpo-45195: Fix test_readline.test_nonascii(): sometimes, the newline character is not written at the end, so don't expect it in the output. Patch by Victor Stinner.

  • bpo-45156: Fixes infinite loop on unittest.mock.seal() of mocks created by create_autospec().

  • bpo-45125: Improves pickling tests and docs of SharedMemory and SharableList objects.

  • bpo-44860: Update test_sysconfig.test_user_similar() for the posix_user scheme: platlib doesn't use sys.platlibdir. Patch by Victor Stinner.

  • bpo-25130: Add calls of gc.collect() in tests to support PyPy.


  • bpo-45532: Update sys.version to use main as fallback information. Patch by Jeong YunWon.

  • bpo-45536: The configure script now checks whether OpenSSL headers and libraries provide required APIs. Most common APIs are verified. The check detects outdated or missing OpenSSL. Failures do not stop configure.

  • bpo-45221: Fixed regression in handling of LDFLAGS and CPPFLAGS options where argparse.parse_known_args() could interpret an option as one of the built-in command line argument, for example -h for help.

  • bpo-45405: Prevent internal configure error when running configure with recent versions of non-Apple clang. Patch by David Bohman.

  • bpo-45220: Avoid building with the Windows 11 SDK previews automatically. This may be overridden by setting the DefaultWindowsSDKVersion environment variable before building.

  • bpo-45067: The ncurses function extended_color_content was introduced in 2017

    ( The

    ncurses-devel package in CentOS 7 had a older version ncurses resulted in compilation error. For compiling ncurses with extended color support, we verify the version of the ncurses library >= 20170401.


  • bpo-45337: venv now warns when the created environment may need to be accessed at a different path, due to redirections, links or junctions. It also now correctly installs or upgrades components when the alternate path is required.


  • bpo-34602: When building CPython on macOS with ./configure --with-undefined-behavior-sanitizer --with-pydebug, the stack size is now quadrupled to allow for the entire test suite to pass.


  • bpo-45495: Add context keywords 'case' and 'match' to completions list.

  • bpo-45296: On Windows, change exit/quit message to suggest Ctrl-D, which works, instead of <Ctrl-Z Return>, which does not work in IDLE.

  • bpo-45193: Make completion boxes appear on Ubuntu again.


  • bpo-44786: Fix a warning in regular expression in the c-analyzer script.


  • bpo-45307: Restore the private C API function _PyImport_FindExtensionObject(). It will be removed in Python 3.11.

  • bpo-44687: BufferedReader.peek() no longer raises ValueError when the entire file has already been buffered.

  • bpo-44751: Remove crypt.h include from the public Python.h header.

Python 3.10.0 final

Release date: 2021-10-04

Core and Builtins

  • bpo-45121: Fix issue where Protocol.__init__ raises RecursionError when it's called directly or via super(). Patch provided by Yurii Karabas.



  • bpo-45216: Remove extra documentation listing methods in difflib. It was rendering twice in pydoc and was outdated in some places.

  • bpo-45024: documentation has been expanded to explicitly cover how instance and subclass checks work, with additional doctest examples and an exhaustive list of ABCs which test membership purely by presence of the right special methods. Patch by Raymond Hettinger.


  • bpo-45128: Fix test_multiprocessing_fork failure due to test_logging and sys.modules manipulation.

  • bpo-44860: Update test_sysconfig.test_user_similar() for the posix_user scheme: platlib doesn't use sys.platlibdir. Patch by Victor Stinner.



  • bpo-45193: Make completion boxes appear on Ubuntu again.


  • bpo-45307: Restore the private C API function _PyImport_FindExtensionObject(). It will be removed in Python 3.11.

Python 3.10.0 release candidate 2

Release date: 2021-09-07


  • bpo-42278: Replaced usage of tempfile.mktemp() with TemporaryDirectory to avoid a potential race condition.

  • bpo-44394: Update the vendored copy of libexpat to 2.4.1 (from 2.2.8) to get the fix for the CVE-2013-0340 "Billion Laughs" vulnerability. This copy is most used on Windows and macOS.

  • bpo-43124: Made the internal putcmd function in smtplib sanitize input for presence of \r and \n characters to avoid (unlikely) command injection.

Core and Builtins

  • bpo-45123: Fix PyAiter_Check to only check for the __anext__ presence (not for __aiter__). Rename PyAiter_Check to PyAIter_Check, PyObject_GetAiter -> PyObject_GetAIter.

  • bpo-45018: Fixed pickling of range iterators that iterated for over 2**32 times.

  • bpo-45000: A SyntaxError is now raised when trying to delete __debug__. Patch by Dong-hee Na.

  • bpo-44963: Implement send() and throw() methods for anext_awaitable objects. Patch by Pablo Galindo.

  • bpo-44962: Fix a race in WeakKeyDictionary, WeakValueDictionary and WeakSet when two threads attempt to commit the last pending removal. This fixes asyncio.create_task and fixes a data loss in where shutdown_asyncgens is not run

  • bpo-44954: Fixed a corner case bug where the result of float.fromhex('0x.8p-1074') was rounded the wrong way.

  • bpo-44947: Refine the syntax error for trailing commas in import statements. Patch by Pablo Galindo.

  • bpo-44698: Restore behaviour of complex exponentiation with integer-valued exponent of type float or complex.

  • bpo-44885: Correct the ast locations of f-strings with format specs and repeated expressions. Patch by Pablo Galindo

  • bpo-44872: Use new trashcan macros (Py_TRASHCAN_BEGIN/END) in frameobject.c instead of the old ones (Py_TRASHCAN_SAFE_BEGIN/END).

  • bpo-33930: Fix segmentation fault with deep recursion when cleaning method objects. Patch by Augusto Goulart and Pablo Galindo.

  • bpo-25782: Fix bug where PyErr_SetObject hangs when the current exception has a cycle in its context chain.

  • bpo-44856: Fix reference leaks in the error paths of update_bases() and __build_class__. Patch by Pablo Galindo.

  • bpo-44838: Fixed a bug that was causing the parser to raise an incorrect custom SyntaxError for invalid 'if' expressions. Patch by Pablo Galindo.

  • bpo-44584: The threading debug (PYTHONTHREADDEBUG environment variable) is deprecated in Python 3.10 and will be removed in Python 3.12. This feature requires a debug build of Python. Patch by Victor Stinner.

  • bpo-39091: Fix crash when using passing a non-exception to a generator's throw() method. Patch by Noah Oxer


  • bpo-45081: Fix issue when dataclasses that inherit from typing.Protocol subclasses have wrong __init__. Patch provided by Yurii Karabas.

  • bpo-41620: run() now always return a TestResult instance. Previously it returned None if the test class or method was decorated with a skipping decorator.

  • bpo-43913: Fix bugs in cleaning up classes and modules in unittest:

    • Functions registered with addModuleCleanup() were not called unless the user defines tearDownModule() in their test module.

    • Functions registered with addClassCleanup() were not called if tearDownClass is set to None.

    • Buffering in TestResult did not work with functions registered with addClassCleanup() and addModuleCleanup().

    • Errors in functions registered with addClassCleanup() and addModuleCleanup() were not handled correctly in buffered and debug modes.

    • Errors in setUpModule() and functions registered with addModuleCleanup() were reported in wrong order.

    • And several lesser bugs.

  • bpo-45030: Fix integer overflow in pickling and copying the range iterator.

  • bpo-45001: Made email date parsing more robust against malformed input, namely a whitespace-only Date: header. Patch by Wouter Bolsterlee.

  • bpo-44449: Fix a crash in the signal handler of the faulthandler module: no longer modify the reference count of frame objects. Patch by Victor Stinner.

  • bpo-44955: Method stopTestRun() is now always called in pair with method startTestRun() for TestResult objects implicitly created in run(). Previously it was not called for test methods and classes decorated with a skipping decorator.

  • bpo-44935: subprocess on Solaris now also uses os.posix_spawn() for better performance.

  • bpo-44911: IsolatedAsyncioTestCase will no longer throw an exception while cancelling leaked tasks. Patch by Bar Harel.

  • bpo-44524: Make exception message more useful when subclass from typing special form alias. Patch provided by Yurii Karabas.

  • bpo-38956: argparse.BooleanOptionalAction's default value is no longer printed twice when used with argparse.ArgumentDefaultsHelpFormatter.

  • bpo-44860: Fix the posix_user scheme in sysconfig to not depend on sys.platlibdir.

  • bpo-44581: Upgrade bundled pip to 21.2.3 and setuptools to 57.4.0

  • bpo-44849: Fix the os.set_inheritable() function on FreeBSD 14 for file descriptor opened with the O_PATH flag: ignore the EBADF error on ioctl(), fallback on the fcntl() implementation. Patch by Victor Stinner.

  • bpo-44605: The @functools.total_ordering() decorator now works with metaclasses.

  • bpo-44524: Fixed an issue wherein the __name__ and __qualname__ attributes of subscribed specialforms could be None.

  • bpo-44822: sqlite3 user-defined functions and aggregators returning strings with embedded NUL characters are no longer truncated. Patch by Erlend E. Aasland.

  • bpo-44801: Ensure that the ParamSpec variable in Callable can only be substituted with a parameters expression (a list of types, an ellipsis, ParamSpec or Concatenate).

  • bpo-27334: The sqlite3 context manager now performs a rollback (thus releasing the database lock) if commit failed. Patch by Luca Citi and Erlend E. Aasland.

  • bpo-41402: Fix email.message.EmailMessage.set_content() when called with binary data and 7bit content transfer encoding.

  • bpo-32695: The compresslevel and preset keyword arguments of are now both documented and tested.

  • bpo-34990: Fixed a Y2k38 bug in the compileall module where it would fail to compile files with a modification time after the year 2038.

  • bpo-38840: Fix test___all__ on platforms lacking a shared memory implementation.

  • bpo-26228: pty.spawn no longer hangs on FreeBSD, macOS, and Solaris.

  • bpo-33349: lib2to3 now recognizes async generators everywhere.


  • bpo-44957: Promote PEP 604 union syntax by using it where possible. Also, mention X | Y more prominently in section about Union and mention X | None at all in section about Optional.

  • bpo-44903: Removed the othergui.rst file, any references to it, and the list of GUI frameworks in the FAQ. In their place I've added links to the Python Wiki page on GUI frameworks.

  • bpo-33479: Tkinter documentation has been greatly expanded with new "Architecture" and "Threading model" sections.

  • bpo-36700: base64 RFC references were updated to point to RFC 4648; a section was added to point users to the new "security considerations" section of the RFC.

  • bpo-44756: Reverted automated virtual environment creation on make html when building documentation. It turned out to be disruptive for downstream distributors.

  • bpo-42958: Updated the docstring and docs of filecmp.cmp() to be more accurate and less confusing especially in respect to shallow arg.

  • bpo-43066: Added a warning to zipfile docs: filename arg with a leading slash may cause archive to be un-openable on Windows systems.

  • bpo-39452: Rewrote Doc/library/__main__.rst. Broadened scope of the document to explicitly discuss and differentiate between in packages versus the __name__ == '__main__' expression (and the idioms that surround it).

  • bpo-27752: Documentation of csv.Dialect is more descriptive.

  • bpo-41576: document BaseException in favor of bare except

  • bpo-39498: Add a "Security Considerations" index which links to standard library modules that have explicitly documented security considerations.

  • bpo-33479: Remove the unqualified claim that tkinter is threadsafe. It has not been true for several years and likely never was. An explanation of what is true may be added later, after more discussion, and possibly after patching _tkinter.c,


  • bpo-45052: WithProcessesTestSharedMemory.test_shared_memory_basics test was ignored, because self.assertEqual(sms.size, sms2.size) line was failing. It is now removed and test is unskipped.

    The main motivation for this line to be removed from the test is that the size of SharedMemory is not ever guaranteed to be the same. It is decided by the platform.

  • bpo-45042: Fixes that test classes decorated with @hashlib_helper.requires_hashdigest were skipped all the time.

  • bpo-45011: Made tests relying on the _asyncio C extension module optional to allow running on alternative Python implementations. Patch by Serhiy Storchaka.

  • bpo-44949: Fix auto history tests of test_readline: sometimes, the newline character is not written at the end, so don't expect it in the output.

  • bpo-44891: Tests were added to clarify id() is preserved when obj * 1 is used on str and bytes objects. Patch by Nikita Sobolev.

  • bpo-44852: Add ability to wholesale silence DeprecationWarnings while running the regression test suite.

  • bpo-40928: Notify users running test_decimal regression tests on macOS of potential harmless "malloc can't allocate region" messages spewed by test_decimal.


  • bpo-45007: Update to OpenSSL 1.1.1l in Windows build


  • bpo-45007: Update macOS installer builds to use OpenSSL 1.1.1l.

  • bpo-44689: ctypes.util.find_library() now works correctly on macOS 11 Big Sur even if Python is built on an older version of macOS. Previously, when built on older macOS systems, find_library was not able to find macOS system libraries when running on Big Sur due to changes in how system libraries are stored.

Python 3.10.0 release candidate 1

Release date: 2021-08-02


  • bpo-44600: Fix incorrect line numbers while tracing some failed patterns in match statements. Patch by Charles Burkland.

Core and Builtins

  • bpo-44792: Improve syntax errors for if expressions. Patch by Miguel Brito

  • bpo-34013: Generalize the invalid legacy statement custom error message (like the one generated when "print" is called without parentheses) to include more generic expressions. Patch by Pablo Galindo

  • bpo-44732: Rename types.Union to types.UnionType.

  • bpo-44698: Fix undefined behaviour in complex object exponentiation.

  • bpo-44653: Support typing types in parameter substitution in the union type.

  • bpo-44676: Add ability to serialise types.Union objects. Patch provided by Yurii Karabas.

  • bpo-44633: Parameter substitution of the union type with wrong types now raises TypeError instead of returning NotImplemented.

  • bpo-44662: Add __module__ to types.Union. This also fixes types.Union issues with typing.Annotated. Patch provided by Yurii Karabas.

  • bpo-44655: Include the name of the type in unset __slots__ attribute errors. Patch by Pablo Galindo

  • bpo-44655: Don't include a missing attribute with the same name as the failing one when offering suggestions for missing attributes. Patch by Pablo Galindo

  • bpo-44646: Fix the hash of the union type: it no longer depends on the order of arguments.

  • bpo-44636: Collapse union of equal types. E.g. the result of int | int is now int. Fix comparison of the union type with non-hashable objects. E.g. int | str == {} no longer raises a TypeError.

  • bpo-44635: Convert None to type(None) in the union type constructor.

  • bpo-44589: Mapping patterns in match statements with two or more equal literal keys will now raise a SyntaxError at compile-time.

  • bpo-44606: Fix __instancecheck__ and __subclasscheck__ for the union type.

  • bpo-42073: The @classmethod decorator can now wrap other classmethod-like descriptors.

  • bpo-44490: typing now searches for type parameters in types.Union objects. get_type_hints will also properly resolve annotations with nested types.Union objects. Patch provided by Yurii Karabas.

  • bpo-44490: Add __parameters__ attribute and __getitem__ operator to types.Union. Patch provided by Yurii Karabas.

  • bpo-44472: Fix ltrace functionality when exceptions are raised. Patch by Pablo Galindo


  • bpo-44806: Non-protocol subclasses of typing.Protocol ignore now the __init__ method inherited from protocol base classes.

  • bpo-44793: Fix checking the number of arguments when subscribe a generic type with ParamSpec parameter.

  • bpo-44784: In importlib.metadata tests, override warnings behavior under expected DeprecationWarnings (importlib_metadata 4.6.3).

  • bpo-44667: The tokenize.tokenize() doesn't incorrectly generate a NEWLINE token if the source doesn't end with a new line character but the last line is a comment, as the function is already generating a NL token. Patch by Pablo Galindo

  • bpo-44752: rcompleter does not call getattr() on property objects to avoid the side-effect of evaluating the corresponding method.

  • bpo-44720: weakref.proxy objects referencing non-iterators now raise TypeError rather than dereferencing the null tp_iternext slot and crashing.

  • bpo-44704: The implementation of now matches that of frozenset.__hash__().

  • bpo-44666: Fixed issue in compileall.compile_file() when sys.stdout is redirected. Patch by Stefan Hölzl.

  • bpo-42854: Fixed a bug in the _ssl module that was throwing OverflowError when using _ssl._SSLSocket.write() and for a big value of the len parameter. Patch by Pablo Galindo

  • bpo-44353: Refactor typing.NewType from function into callable class. Patch provided by Yurii Karabas.

  • bpo-44524: Add missing __name__ and __qualname__ attributes to typing module classes. Patch provided by Yurii Karabas.

  • bpo-40897: Give priority to using the current class constructor in inspect.signature(). Patch by Weipeng Hong.

  • bpo-44648: Fixed wrong error being thrown by inspect.getsource() when examining a class in the interactive session. Instead of TypeError, it should be OSError with appropriate error message.

  • bpo-44608: Fix memory leak in _tkinter._flatten() if it is called with a sequence or set, but not list or tuple.

  • bpo-44559: [Enum] module reverted to 3.9; 3.10 changes pushed until 3.11

  • bpo-41928: Update shutil.copyfile() to raise FileNotFoundError instead of confusing IsADirectoryError when a path ending with a os.path.sep does not exist; shutil.copy() and shutil.copy2() are also affected.

  • bpo-44566: handle StopIteration subclass raised from @contextlib.contextmanager generator

  • bpo-41249: Fixes TypedDict to work with typing.get_type_hints() and postponed evaluation of annotations across modules.

  • bpo-44461: Fix bug with pdb's handling of import error due to a package which does not have a __main__ module

  • bpo-43625: Fix a bug in the detection of CSV file headers by csv.Sniffer.has_header() and improve documentation of same.

  • bpo-42892: Fixed an exception thrown while parsing a malformed multipart email by email.message.EmailMessage.

  • bpo-27827: pathlib.PureWindowsPath.is_reserved() now identifies a greater range of reserved filenames, including those with trailing spaces or colons.

  • bpo-38741: configparser: using ']' inside a section header will no longer cut the section name short at the ']'

  • bpo-27513: email.utils.getaddresses() now accepts email.header.Header objects along with string values. Patch by Zackery Spytz.

  • bpo-29298: Fix TypeError when required subparsers without dest do not receive arguments. Patch by Anthony Sottile.


  • bpo-44740: Replaced occurences of uppercase "Web" and "Internet" with lowercase versions per the 2016 revised Associated Press Style Book.

  • bpo-44693: Update the definition of __future__ in the glossary by replacing the confusing word "pseudo-module" with a more accurate description.

  • bpo-35183: Add typical examples to os.path.splitext docs

  • bpo-30511: Clarify that shutil.make_archive() is not thread-safe due to reliance on changing the current working directory.

  • bpo-44561: Update of three expired hyperlinks in Doc/distributing/index.rst: "Project structure", "Building and packaging the project", and "Uploading the project to the Python Packaging Index".

  • bpo-44613: importlib.metadata is no longer provisional.

  • bpo-44544: List all kwargs for textwrap.wrap(), textwrap.fill(), and textwrap.shorten(). Now, there are nav links to attributes of TextWrap, which makes navigation much easier while minimizing duplication in the documentation.

  • bpo-44453: Fix documentation for the return type of sysconfig.get_path().


  • bpo-44734: Fixed floating point precision issue in turtle tests.

  • bpo-44708: Regression tests, when run with -w, are now re-running only the affected test methods instead of re-running the entire test file.

  • bpo-44647: Added a permanent Unicode-valued environment variable to regression tests to ensure they handle this use case in the future. If your test environment breaks because of that, report a bug to us, and temporarily set PYTHONREGRTEST_UNICODE_GUARD=0 in your test environment.

  • bpo-44515: Adjust recently added contextlib tests to avoid assuming the use of a refcounted GC



  • bpo-41972: The framework build's user header path in sysconfig is changed to add a 'pythonX.Y' component to match distutils's behavior.

  • bpo-34932: Add socket.TCP_KEEPALIVE support for macOS. Patch by Shane Harvey.


  • bpo-44756: In the Makefile for documentation (Doc/Makefile), the build rule is dependent on the venv rule. Therefore, html, latex, and other build-dependent rules are also now dependent on venv. The venv rule only performs an action if $(VENVDIR) does not exist. Doc/README.rst was updated; most users now only need to type make html.


  • bpo-41103: Reverts removal of the old buffer protocol because they are part of stable ABI.

  • bpo-42747: The Py_TPFLAGS_HAVE_VERSION_TAG type flag now does nothing. The Py_TPFLAGS_HAVE_AM_SEND flag (which was added in 3.10) is removed. Both were unnecessary because it is not possible to have type objects with the relevant fields missing.

Python 3.10.0 beta 4

Release date: 2021-07-10


  • bpo-41180: Add auditing events to the marshal module, and stop raising code.__init__ events for every unmarshalled code object. Directly instantiated code objects will continue to raise an event, and audit event handlers should inspect or collect the raw marshal data. This reduces a significant performance overhead when loading from .pyc files.

Core and Builtins

  • bpo-44562: Remove uses of PyObject_GC_Del() in error path when initializing types.GenericAlias.

  • bpo-41486: Fix a memory consumption and copying performance regression in earlier 3.10 beta releases if someone used an output buffer larger than 4GiB with zlib.decompress on input data that expands that large.

  • bpo-44553: Implement GC methods for types.Union to break reference cycles and prevent memory leaks.

  • bpo-44523: Remove the pass-through for hash() of weakref.proxy objects to prevent unintended consequences when the original referred object dies while the proxy is part of a hashable object. Patch by Pablo Galindo.

  • bpo-44483: Fix a crash in types.Union objects when creating a union of an object with bad __module__ field.

  • bpo-44297: Make sure that the line number is set when entering a comprehension scope. Ensures that backtraces inclusing generator expressions show the correct line number.

  • bpo-44456: Improve the syntax error when mixing positional and keyword patterns. Patch by Pablo Galindo.

  • bpo-44368: Improve syntax errors for invalid "as" targets. Patch by Pablo Galindo

  • bpo-44317: Improve tokenizer error with improved locations. Patch by Pablo Galindo.

  • bpo-43667: Improve Unicode support in non-UTF locales on Oracle Solaris. This issue does not affect other Solaris systems.


  • bpo-44558: Make the implementation consistency of indexOf() between C and Python versions. Patch by Dong-hee Na.

  • bpo-34798: Break up paragraph about pprint.PrettyPrinter construction parameters to make it easier to read.

  • bpo-44516: Update vendored pip to 21.1.3

  • bpo-44468: typing.get_type_hints() now finds annotations in classes and base classes with unexpected __module__. Previously, it skipped those MRO elements.

  • bpo-43977: Set the proper Py_TPFLAGS_MAPPING and Py_TPFLAGS_SEQUENCE flags for subclasses created before a parent has been registered as a or

  • bpo-44482: Fix very unlikely resource leak in glob in alternate Python implementations.

  • bpo-44466: The faulthandler module now detects if a fatal error occurs during a garbage collector collection. Patch by Victor Stinner.

  • bpo-44404: tkinter's after() method now supports callables without the __name__ attribute.

  • bpo-44458: BUFFER_BLOCK_SIZE is now declared static, to avoid linking collisions when bz2, lmza or zlib are statically linked.

  • bpo-44464: Remove exception for flake8 in deprecated importlib.metadata interfaces. Sync with importlib_metadata 4.6.

  • bpo-44446: Take into account that lineno might be None in traceback.FrameSummary.

  • bpo-44439: Fix in bz2.BZ2File.write() / lzma.LZMAFile.write() methods, when the input data is an object that supports the buffer protocol, the file length may be wrong.

  • bpo-44434: _thread.start_new_thread() no longer calls PyThread_exit_thread() explicitly at the thread exit, the call was redundant. On Linux with the glibc, pthread_exit() aborts the whole process if dlopen() fails to open file (ex: EMFILE error). Patch by Victor Stinner.

  • bpo-44395: Fix as_string() to pass unixfrom properly. Patch by Dong-hee Na.

  • bpo-34266: Handle exceptions from parsing the arg of pdb's run/restart command.

  • bpo-44077: It's now possible to receive the type of service (ToS), a.k.a. differentiated services (DS), a.k.a. differenciated services code point (DSCP) and excplicit congestion notification (ECN) IP header fields with socket.IP_RECVTOS.

  • bpo-43024: Improve the help signature of traceback.print_exception(), traceback.format_exception() and traceback.format_exception_only().

  • bpo-30256: Pass multiprocessing BaseProxy argument manager_owned through AutoProxy.


  • bpo-44558: Match the docstring and python implementation of countOf() to the behavior of its c implementation.

  • bpo-38062: Clarify that atexit uses equality comparisons internally.

  • bpo-40620: Convert examples in tutorial controlflow.rst section 4.3 to be interpreter-demo style.

  • bpo-13814: In the Design FAQ, answer "Why don't generators support the with statement?"

  • bpo-41621: Document that collections.defaultdict parameter default_factory defaults to None and is positional-only.


  • bpo-44287: Fix asyncio test_popen() of test_windows_utils by using a longer timeout. Use military grade battle-tested timeout rather than a hardcoded timeout of 10 seconds: it's 30 seconds by default, but it is made longer on slow buildbots. Patch by Victor Stinner.

  • bpo-44451: Reset DeprecationWarning filters in test.test_importlib.test_metadata_api.APITests.test_entry_points_by_index to avoid StopIteration error if DeprecationWarnings are ignored.

  • bpo-30256: Add test for nested queues when using multiprocessing shared objects AutoProxy[Queue] inside ListProxy and DictProxy


  • bpo-44535: Enable building using a Visual Studio 2022 install on Windows.

  • bpo-43298: Improved error message when building without a Windows SDK installed.



Python 3.10.0 beta 3

Release date: 2021-06-17

Core and Builtins

  • bpo-44409: Fix error location information for tokenizer errors raised on initialization of the tokenizer. Patch by Pablo Galindo.

  • bpo-44396: Fix a possible crash in the tokenizer when raising syntax errors for unclosed strings. Patch by Pablo Galindo.

  • bpo-44349: Fix an edge case when displaying text from files with encoding in syntax errors. Patch by Pablo Galindo.

  • bpo-44335: Fix a regression when identifying incorrect characters in syntax errors. Patch by Pablo Galindo

  • bpo-44304: Fix a crash in the sqlite3 module that happened when the garbage collector clears sqlite.Statement objects. Patch by Pablo Galindo

  • bpo-44305: Improve error message for try blocks without except or finally blocks. Patch by Pablo Galindo.

  • bpo-43833: Emit a deprecation warning if the numeric literal is immediately followed by one of keywords: and, else, for, if, in, is, or. Raise a syntax error with more informative message if it is immediately followed by other keyword or identifier.

  • bpo-11105: When compiling ast.AST objects with recursive references through compile(), the interpreter doesn't crash anymore instead it raises a RecursionError.


  • bpo-42972: The _thread.RLock type now fully implement the GC protocol: add a traverse function and the Py_TPFLAGS_HAVE_GC flag. Patch by Victor Stinner.

  • bpo-44422: The threading.enumerate() function now uses a reentrant lock to prevent a hang on reentrant call. Patch by Victor Stinner.

  • bpo-44389: Fix deprecation of ssl.OP_NO_TLSv1_3

  • bpo-44362: Improve ssl module's deprecation messages, error reporting, and documentation for deprecations.

  • bpo-44342: [Enum] Change pickling from by-value to by-name.

  • bpo-44356: [Enum] Allow multiple data-type mixins if they are all the same.

  • bpo-44351: Restore back parse_makefile() in distutils.sysconfig because it behaves differently than the similar implementation in sysconfig.

  • bpo-44242: Remove missing flag check from Enum creation and move into a verify decorator.

  • bpo-44246: In importlib.metadata, restore compatibility in the result from Distribution.entry_points (EntryPoints) to honor expectations in older implementations and issuing deprecation warnings for these cases: A. EntryPoints objects are once again mutable, allowing for sort() and other list-based mutation operations. Avoid deprecation warnings by casting to a mutable sequence (e.g. list(dist.entry_points).sort()). B. EntryPoints results once again allow for access by index. To avoid deprecation warnings, cast the result to a Sequence first (e.g. tuple(dist.entry_points)[0]).

  • bpo-44246: In importlib.metadata.entry_points, de-duplication of distributions no longer requires loading the full metadata for PathDistribution objects, improving entry point loading performance by ~10x.

  • bpo-43853: Improved string handling for sqlite3 user-defined functions and aggregates:

    • It is now possible to pass strings with embedded null characters to UDFs

    • Conversion failures now correctly raise MemoryError

    Patch by Erlend E. Aasland.

  • bpo-43318: Fix a bug where pdb does not always echo cleared breakpoints.

  • bpo-37022: pdb now displays exceptions from repr() with its p and pp commands.


  • bpo-44392: Added a new section in the C API documentation for types used in type hinting. Documented Py_GenericAlias and Py_GenericAliasType.

  • bpo-38291: Mark and as deprecated since Python 3.8 in the documentation. They were never properly supported by type checkers.

  • bpo-44322: Document that SyntaxError args have a details tuple and that details are adjusted for errors in f-string field replacement expressions.


  • bpo-44363: Account for address sanitizer in test_capi. test_capi now passes when run GCC address sanitizer.

  • bpo-43921: Fix test_ssl.test_wrong_cert_tls13(): use suppress_ragged_eofs=False, since read() can raise ssl.SSLEOFError on Windows. Patch by Victor Stinner.

  • bpo-43921: Fix test_pha_required_nocert() of test_ssl: catch two more EOF cases (when the recv() method returns an empty string). Patch by Victor Stinner.


  • bpo-44381: The Windows build now accepts EnableControlFlowGuard set to guard to enable CFG.


  • bpo-40128: Mostly fix completions on macOS when not using tcl/tk 8.6.11 (as with 3.9). The added update_idletask call should be harmless and possibly helpful otherwise.

  • bpo-33962: Move the indent space setting from the Font tab to the new Windows tab. Patch by Mark Roseman and Terry Jan Reedy.

  • bpo-40468: Split the settings dialog General tab into Windows and Shell/ED tabs. Move help sources, which extend the Help menu, to the Extensions tab. Make space for new options and shorten the dialog. The latter makes the dialog better fit small screens.


Python 3.10.0 beta 2

Release date: 2021-05-31


  • bpo-44022: mod:http.client now avoids infinitely reading potential HTTP headers after a 100 Continue status response from the server.

Core and Builtins

  • bpo-43667: Improve Unicode support in non-UTF locales on Oracle Solaris. This issue does not affect other Solaris systems.

  • bpo-44232: Fix a regression in type() when a metaclass raises an exception. The C function type_new() must properly report the exception when a metaclass constructor raises an exception and the winner class is not the metaclass. Patch by Victor Stinner.

  • bpo-44201: Avoid side effects of checking for specialized syntax errors in the REPL that was causing it to ask for extra tokens after a syntax error had been detected. Patch by Pablo Galindo

  • bpo-44184: Fix a crash at Python exit when a deallocator function removes the last strong reference to a heap type. Patch by Victor Stinner.

  • bpo-44180: The parser doesn't report generic syntax errors that happen in a position further away that the one it reached in the first pass. Patch by Pablo Galindo

  • bpo-44168: Fix error message in the parser involving keyword arguments with invalid expressions. Patch by Pablo Galindo

  • bpo-44143: Fixed a crash in the parser that manifest when raising tokenizer errors when an existing exception was present. Patch by Pablo Galindo.

  • bpo-44114: Fix incorrect dictkeys_reversed and dictitems_reversed function signatures in C code, which broke webassembly builds.

  • bpo-43149: Corrent the syntax error message regarding multiple exception types to not refer to "exception groups". Patch by Pablo Galindo

  • bpo-44056: Syntax errors when default except is not the last except are reported with the correct location. Patch by Mark Shannon.

  • bpo-43822: The parser will prioritize tokenizer errors over custom syntax errors when raising exceptions. Patch by Pablo Galindo.

  • bpo-28146: Fix a confusing error message in str.format().


  • bpo-44254: On Mac, give turtledemo button text a color that works on both light or dark background. Programmers cannot control the latter.

  • bpo-38693: Prefer f-strings to .format in importlib.resources.

  • bpo-33693: Importlib.metadata now prefers f-strings to .format.

  • bpo-44241: Incorporate minor tweaks from importlib_metadata 4.1: SimplePath protocol, support for Metadata 2.2.

  • bpo-44210: Make importlib.metadata._meta.PackageMetadata public.

  • bpo-43643: Declare as a property per the spec.

  • bpo-33433: For IPv4 mapped IPv6 addresses (RFC 4291 Section, the ipaddress.IPv6Address.is_private check is deferred to the mapped IPv4 address. This solves a bug where public mapped IPv4 addresses were considered private by the IPv6 check.

  • bpo-44145: hmac computations were not releasing the GIL while calling the OpenSSL HMAC_Update C API (a new feature in 3.9). This unintentionally prevented parallel computation as other hashlib algorithms support.

  • bpo-37788: Fix a reference leak when a Thread object is never joined.

  • bpo-38908: Subclasses of typing.Protocol which only have data variables declared will now raise a TypeError when checked with isinstance unless they are decorated with runtime_checkable(). Previously, these checks passed silently. Patch provided by Yurii Karabas.

  • bpo-44098: typing.ParamSpec will no longer be found in the __parameters__ of most typing generics except in valid use locations specified by PEP 612. This prevents incorrect usage like typing.List[P][int]. This change means incorrect usage which may have passed silently in 3.10 beta 1 and earlier will now error.

  • bpo-44089: Allow subclassing csv.Error in 3.10 (it was allowed in 3.9 and earlier but was disallowed in early versions of 3.10).

  • bpo-44059: Register the SerenityOS Browser in the webbrowser module.

  • bpo-36515: The hashlib module no longer does unaligned memory accesses when compiled for ARM platforms.

  • bpo-44018: random.seed() no longer mutates bytearray inputs.

  • bpo-38352: Add IO, BinaryIO, TextIO, Match, and Pattern to typing.__all__. Patch by Jelle Zijlstra.

  • bpo-43972: When http.server.SimpleHTTPRequestHandler sends a 301 (Moved Permanently) for a directory path not ending with /, add a Content-Length: 0 header. This improves the behavior for certain clients.

  • bpo-28528: Fix a bug in pdb where checkline() raises AttributeError if it is called after reset().

  • bpo-43650: Fix MemoryError in shutil.unpack_archive() which fails inside shutil._unpack_zipfile() on large files. Patch by Igor Bolshakov.

  • bpo-41730: DeprecationWarning is now raised when importing tkinter.tix, which has been deprecated in documentation since Python 3.6.


  • bpo-42392: Document the deprecation and removal of the loop parameter for many functions and classes in asyncio.

  • bpo-44195: Corrected references to TraversableResources in docs. There is no TraversableReader.

  • bpo-41963: Document that ConfigParser strips off comments when reading configuration files.

  • bpo-44072: Correct where in the numeric ABC hierarchy ** support is added, i.e., in numbers.Complex, not numbers.Integral.

  • bpo-43558: Add the remark to dataclasses documentation that the __init__() of any base class has to be called in __post_init__(), along with a code example.

  • bpo-44025: Clarify when '_' in match statements is a keyword, and when not.


  • bpo-31904: Ignore error string case in test_py_compile test_file_not_exists().

  • bpo-42083: Add test to check that PyStructSequence_NewType accepts a PyStructSequence_Desc with doc field set to NULL.

  • bpo-35753: Fix crash in doctest when doctest parses modules that include unwrappable functions by skipping those functions.


  • bpo-41282: Fix broken make install that caused standard library extension modules to be unnecessarily and incorrectly rebuilt during the install phase of cpython.


  • bpo-42686: Build sqlite3 with math functions enabled. Patch by Erlend E. Aasland.


  • bpo-43109: Allow --with-lto configure option to work with Apple-supplied Xcode or Command Line Tools.


  • bpo-41611: Avoid uncaught exceptions in AutoCompleteWindow.winconfig_event().

  • bpo-41611: Fix IDLE sometimes freezing upon tab-completion on macOS.

  • bpo-44010: Highlight the new match statement's soft keywords: match, case, and _. However, this highlighting is not perfect and will be incorrect in some rare cases, including some _-s in case patterns.

  • bpo-44026: Include interpreter's typo fix suggestions in message line for NameErrors and AttributeErrors. Patch by E. Paine.


  • bpo-44074: Make patchcheck automatically detect the correct base branch name (previously it was hardcoded to 'master')


Python 3.10.0 beta 1

Release date: 2021-05-03


  • bpo-43434: Creating sqlite3.Connection objects now also produces sqlite3.connect and sqlite3.connect/handle auditing events. Previously these events were only produced by sqlite3.connect() calls. Patch by Erlend E. Aasland.

  • bpo-43998: The ssl module sets more secure cipher suites defaults. Ciphers without forward secrecy and with SHA-1 MAC are disabled by default. Security level 2 prohibits weak RSA, DH, and ECC keys with less than 112 bits of security. SSLContext defaults to minimum protocol version TLS 1.2. Settings are based on Hynek Schlawack's research.

  • bpo-43882: The presence of newline or tab characters in parts of a URL could allow some forms of attacks.

    Following the controlling specification for URLs defined by WHATWG urllib.parse() now removes ASCII newlines and tabs from URLs, preventing such attacks.

  • bpo-43472: Ensures interpreter-level audit hooks receive the cpython.PyInterpreterState_New event when called through the _xxsubinterpreters module.

  • bpo-43362: Fix invalid free in _sha3 module. The issue was introduced in 3.10.0a1. Python 3.9 and earlier are not affected.

  • bpo-43762: Add audit events for sqlite3.connect/handle(), sqlite3.Connection.enable_load_extension(), and sqlite3.Connection.load_extension(). Patch by Erlend E. Aasland.

  • bpo-43756: Add new audit event glob.glob/2 to incorporate the new root_dir and dir_fd arguments added to glob.glob() and glob.iglob().

  • bpo-36384: ipaddress module no longer accepts any leading zeros in IPv4 address strings. Leading zeros are ambiguous and interpreted as octal notation by some libraries. For example the legacy function socket.inet_aton() treats leading zeros as octal notatation. glibc implementation of modern inet_pton() does not accept any leading zeros. For a while the ipaddress module used to accept ambiguous leading zeros.

  • bpo-43075: Fix Regular Expression Denial of Service (ReDoS) vulnerability in urllib.request.AbstractBasicAuthHandler. The ReDoS-vulnerable regex has quadratic worst-case complexity and it allows cause a denial of service when identifying crafted invalid RFCs. This ReDoS issue is on the client side and needs remote attackers to control the HTTP server.

  • bpo-42800: Audit hooks are now fired for frame.f_code, traceback.tb_frame, and generator code/frame attribute access.

  • bpo-37363: Add audit events to the http.client module.

Core and Builtins

  • bpo-43977: Prevent classes being both a sequence and a mapping when pattern matching.

  • bpo-43977: Use tp_flags on the class object to determine if the subject is a sequence or mapping when pattern matching. Avoids the need to import when pattern matching.

  • bpo-43892: Restore proper validation of complex literal value patterns when parsing match blocks.

  • bpo-43933: Set frame.f_lineno to the line number of the 'with' kweyword when executing the call to __exit__.

  • bpo-43933: If the current position in a frame has no line number then set the f_lineno attribute to None, instead of -1, to conform to PEP 626. This should not normally be possible, but might occur in some unusual circumstances.

  • bpo-43963: Importing the _signal module in a subinterpreter has no longer side effects.

  • bpo-42739: The internal representation of line number tables is changed to not use sentinels, and an explicit length parameter is added to the out of process API function PyLineTable_InitAddressRange. This makes the handling of line number tables more robust in some circumstances.

  • bpo-43908: Make re types immutable. Patch by Erlend E. Aasland.

  • bpo-43908: Make the array.array type immutable. Patch by Erlend E. Aasland.

  • bpo-43901: Change class and module objects to lazy-create empty annotations dicts on demand. The annotations dicts are stored in the object's __dict__ for backwards compatibility.

  • bpo-43892: Match patterns now use new dedicated AST nodes (MatchValue, MatchSingleton, MatchSequence, MatchStar, MatchMapping, MatchClass) rather than reusing expression AST nodes. MatchAs and MatchOr are now defined as pattern nodes rather than as expression nodes. Patch by Nick Coghlan.

  • bpo-42725: Usage of await/yield/yield from and named expressions within an annotation is now forbidden when PEP 563 is activated.

  • bpo-43754: When performing structural pattern matching (PEP 634), captured names are now left unbound until the entire pattern has matched successfully.

  • bpo-42737: Annotations for complex targets (everything beside simple names) no longer cause any runtime effects with from __future__ import annotations.

  • bpo-43914: SyntaxError exceptions raised by the interpreter will highlight the full error range of the expression that consistutes the syntax error itself, instead of just where the problem is detected. Patch by Pablo Galindo.

  • bpo-38605: Revert making from __future__ import annotations the default. This follows the Steering Council decision to postpone PEP 563 changes to at least Python 3.11. See the original email for more information regarding the decision: Patch by Pablo Galindo.

  • bpo-43475: Hashes of NaN values now depend on object identity. Formerly, they always hashed to 0 even though NaN values are not equal to one another. Having the same hash for unequal values caused pile-ups in hash tables.

  • bpo-43859: Improve the error message for IndentationError exceptions. Patch by Pablo Galindo

  • bpo-41323: Constant tuple folding in bytecode optimizer now reuses tuple in constant table.

  • bpo-43846: Data stack usage is much reduced for large literal and call expressions.

  • bpo-38530: When printing NameError raised by the interpreter, PyErr_Display() will offer suggestions of similar variable names in the function that the exception was raised from. Patch by Pablo Galindo

  • bpo-43823: Improve syntax errors for invalid dictionary literals. Patch by Pablo Galindo.

  • bpo-43822: Improve syntax errors in the parser for missing commas between expressions. Patch by Pablo Galindo.

  • bpo-43798: ast.alias nodes now include source location metadata attributes e.g. lineno, col_offset.

  • bpo-43797: Improve SyntaxError error messages for invalid comparisons. Patch by Pablo Galindo.

  • bpo-43760: Move the flag for checking whether tracing is enabled to the C stack, from the heap. Should speed up dispatch in the interpreter.

  • bpo-43682: Static methods (@staticmethod) and class methods (@classmethod) now inherit the method attributes (__module__, __name__, __qualname__, __doc__, __annotations__) and have a new __wrapped__ attribute. Patch by Victor Stinner.

  • bpo-43751: Fixed a bug where anext(ait, default) would erroneously return None.

  • bpo-42128: __match_args__ is no longer allowed to be a list.

  • bpo-43683: Add GEN_START opcode. Marks start of generator, including async, or coroutine and handles sending values to a newly created generator or coroutine.

  • bpo-43105: Importlib now resolves relative paths when creating module spec objects from file locations.

  • bpo-43682: Static methods (@staticmethod) are now callable as regular functions. Patch by Victor Stinner.

  • bpo-42609: Prevented crashes in the AST validator and optimizer when compiling some absurdly long expressions like "+0"*1000000. RecursionError is now raised instead.

  • bpo-38530: When printing AttributeError, PyErr_Display() will offer suggestions of similar attribute names in the object that the exception was raised from. Patch by Pablo Galindo


  • bpo-44015: In @dataclass(), raise a TypeError if KW_ONLY is specified more than once.

  • bpo-25478: Added a total() method to collections.Counter() to compute the sum of the counts.

  • bpo-43733: Change netrc.netrc to use UTF-8 encoding before using locale encoding.

  • bpo-43979: Removed an unnecessary list comprehension before looping from urllib.parse.parse_qsl(). Patch by Christoph Zwerschke and Dong-hee Na.

  • bpo-43993: Update bundled pip to 21.1.1.

  • bpo-43957: [Enum] Deprecate TypeError when non-member is used in a containment check; In 3.12 True or False will be returned instead, and containment will return True if the value is either a member of that enum or one of its members' value.

  • bpo-42904: For backwards compatibility with previous minor versions of Python, if typing.get_type_hints() receives no namespace dictionary arguments, typing.get_type_hints() will search through the global then local namespaces during evaluation of stringized type annotations (string forward references) inside a class.

  • bpo-43945: [Enum] Deprecate non-standard mixin format() behavior: in 3.12 the enum member, not the member's value, will be used for format() calls.

  • bpo-41139: Deprecate undocumented cgi.log() API.

  • bpo-43937: Fixed the turtle module working with non-default root window.

  • bpo-43930: Update bundled pip to 21.1 and setuptools to 56.0.0

  • bpo-43907: Fix a bug in the pure-Python pickle implementation when using protocol 5, where bytearray instances that occur several time in the pickled object graph would incorrectly unpickle into repeated copies of the bytearray object.

  • bpo-43926: In importlib.metadata, provide a uniform interface to Description, allow for any field to be encoded with multiline values, remove continuation lines from multiline values, and add a .json property for easy access to the PEP 566 JSON-compatible form. Sync with importlib_metadata 4.0.

  • bpo-43920: OpenSSL 3.0.0: load_verify_locations() now returns a consistent error message when cadata contains no valid certificate.

  • bpo-43607: urllib can now convert Windows paths with \\?\ prefixes into URL paths.

  • bpo-43817: Add inspect.get_annotations(), which safely computes the annotations defined on an object. It works around the quirks of accessing the annotations from various types of objects, and makes very few assumptions about the object passed in. inspect.get_annotations() can also correctly un-stringize stringized annotations.

    inspect.signature(), inspect.from_callable(), and inspect.from_function() now call inspect.get_annotations() to retrieve annotations. This means inspect.signature() and inspect.from_callable() can now un-stringize stringized annotations, too.

  • bpo-43284: platform.win32_ver derives the windows version from sys.getwindowsversion().platform_version which in turn derives the version from kernel32.dll (which can be of a different version than Windows itself). Therefore change the platform.win32_ver to determine the version using the platform module's _syscmd_ver private function to return an accurate version.

  • bpo-42854: The ssl module now uses SSL_read_ex and SSL_write_ex internally. The functions support reading and writing of data larger than 2 GB. Writing zero-length data no longer fails with a protocol violation error.

  • bpo-42333: Port _ssl extension module to multiphase initialization.

  • bpo-43880: ssl now raises DeprecationWarning for OP_NO_SSL/TLS* options, old TLS versions, old protocols, and other features that have been deprecated since Python 3.6, 3.7, or OpenSSL 1.1.0.

  • bpo-41559: PEP 612 is now implemented purely in Python; builtin types.GenericAlias objects no longer include typing.ParamSpec in __parameters__ (with the exception of's GenericAlias). This means previously invalid uses of ParamSpec (such as list[P]) which worked in earlier versions of Python 3.10 alpha, will now raise TypeError during substitution.

  • bpo-43867: The multiprocessing Server class now explicitly catches SystemExit and closes the client connection in this case. It happens when the Server.serve_client() method reaches the end of file (EOF).

  • bpo-40443: Remove unused imports: pyclbr no longer uses copy, and typing no longer uses ast. Patch by Victor Stinner.

  • bpo-43820: Remove an unneeded copy of the namespace passed to dataclasses.make_dataclass().

  • bpo-43787: Add __iter__() method to bz2.BZ2File, gzip.GzipFile, and lzma.LZMAFile. It makes iterating them about 2x faster. Patch by Inada Naoki.

  • bpo-43680: Deprecate io.OpenWrapper and _pyio.OpenWrapper: use and instead. Until Python 3.9, was not a static method and was set to OpenWrapper to not become a bound method when set to a class variable. is a built-in function whereas is a Python function. In Python 3.10, is now a static method, and is now

  • bpo-43680: The Python function becomes a static method to behave as built-in function: don't become a bound method when stored as a class variable. It becomes possible since static methods are now callable in Python 3.10. Moreover, _pyio.OpenWrapper() becomes a simple alias to Patch by Victor Stinner.

  • bpo-41515: Fix KeyError raised in typing.get_type_hints() due to synthetic modules that don't appear in sys.modules.

  • bpo-43776: When subprocess.Popen args are provided as a string or as pathlib.Path, the Popen instance repr now shows the right thing.

  • bpo-42248: [Enum] ensure exceptions raised in _missing__ are released

  • bpo-43744: fix issue with enum member name matching the start of a private variable name

  • bpo-43772: Fixed the return value of TypeVar.__ror__. Patch by Jelle Zijlstra.

  • bpo-43764: Add match_args parameter to @dataclass decorator to allow suppression of __match_args__ generation.

  • bpo-43799: OpenSSL 3.0.0: define OPENSSL_API_COMPAT 1.1.1 to suppress deprecation warnings. Python requires OpenSSL 1.1.1 APIs.

  • bpo-43478: Mocks can no longer be used as the specs for other Mocks. As a result, an already-mocked object cannot have an attribute mocked using autospec=True or be the subject of a create_autospec(...) call. This can uncover bugs in tests since these Mock-derived Mocks will always pass certain tests (e.g. isinstance()) and builtin assert functions (e.g. assert_called_once_with) will unconditionally pass.

  • bpo-43794: Add ssl.OP_IGNORE_UNEXPECTED_EOF constants (OpenSSL 3.0.0)

  • bpo-43785: Improve bz2.BZ2File performance by removing the RLock from BZ2File. This makes BZ2File thread unsafe in the face of multiple simultaneous readers or writers, just like its equivalent classes in gzip and lzma have always been. Patch by Inada Naoki.

  • bpo-43789: OpenSSL 3.0.0: Don't call the password callback function a second time when first call has signaled an error condition.

  • bpo-43788: The header files for ssl error codes are now OpenSSL version-specific. Exceptions will now show correct reason and library codes. The script has been rewritten to use OpenSSL's text file with error codes.

  • bpo-43766: Implement PEP 647 in the typing module by adding TypeGuard.

  • bpo-25264: os.path.realpath() now accepts a strict keyword-only argument. When set to True, OSError is raised if a path doesn't exist or a symlink loop is encountered.

  • bpo-43780: In importlib.metadata, incorporate changes from importlib_metadata 3.10: Add mtime-based caching during distribution discovery. Flagged use of dict result from entry_points() as deprecated.

  • bpo-47383: The P.args and P.kwargs attributes of typing.ParamSpec are now instances of the new classes typing.ParamSpecArgs and typing.ParamSpecKwargs, which enables a more useful repr(). Patch by Jelle Zijlstra.

  • bpo-43731: Add an encoding parameter logging.fileConfig().

  • bpo-43712: Add encoding and errors parameters to fileinput.input() and fileinput.FileInput.

  • bpo-38659: A simple_enum decorator is added to the enum module to convert a normal class into an Enum. test_simple_enum added to test simple enums against a corresponding normal Enum. Standard library modules updated to use simple_enum.

  • bpo-43764: Fix an issue where __match_args__ generation could fail for some dataclasses.

  • bpo-43752: Fix sqlite3 regression for zero-sized blobs with converters, where b"" was returned instead of None. The regression was introduced by GH-24723. Patch by Erlend E. Aasland.

  • bpo-43655: tkinter dialog windows are now recognized as dialogs by window managers on macOS and X Window.

  • bpo-43723: The following threading methods are now deprecated and should be replaced:

    Patch by Jelle Zijlstra.

  • bpo-2135: Deprecate find_module() and find_loader() implementations in importlib and zipimport.

  • bpo-43534: turtle.textinput() and turtle.numinput() create now a transient window working on behalf of the canvas window.

  • bpo-43532: Add the ability to specify keyword-only fields to dataclasses. These fields will become keyword-only arguments to the generated __init__.

  • bpo-43522: Fix problem with hostname_checks_common_name. OpenSSL does not copy hostflags from struct SSL_CTX to struct SSL.

  • bpo-8978: Improve error message for when lzma / bz2 are unavailable. Patch by Anthony Sottile.

  • bpo-42967: Allow bytes separator argument in urllib.parse.parse_qs and urllib.parse.parse_qsl when parsing str query strings. Previously, this raised a TypeError.

  • bpo-43296: Improve sqlite3 error handling: sqlite3_value_blob() errors that set SQLITE_NOMEM now raise MemoryError. Patch by Erlend E. Aasland.

  • bpo-43312: New functions sysconfig.get_preferred_scheme() and sysconfig.get_default_scheme() are added to query a platform for its preferred "user", "home", and "prefix" (default) scheme names.

  • bpo-43265: Improve sqlite3.Connection.backup() error handling. The error message for non-existent target database names is now unknown database <database name> instead of SQL logic error. Patch by Erlend E. Aasland.

  • bpo-41282: Install schemes in distutils.command.install are now loaded from sysconfig.

  • bpo-41282: distutils.sysconfig has been merged to sysconfig.

  • bpo-43176: Fixed processing of a dataclass that inherits from a frozen dataclass with no fields. It is now correctly detected as an error.

  • bpo-43080: pprint now has support for dataclasses.dataclass. Patch by Lewis Gaul.

  • bpo-39950: Add pathlib.Path.hardlink_to() method that supersedes link_to(). The new method has the same argument order as symlink_to().

  • bpo-42904: typing.get_type_hints() now checks the local namespace of a class when evaluating PEP 563 annotations inside said class.

  • bpo-42269: Add slots parameter to dataclasses.dataclass decorator to automatically generate __slots__ for class. Patch provided by Yurii Karabas.

  • bpo-39529: Deprecated use of asyncio.get_event_loop() without running event loop. Emit deprecation warning for asyncio functions which implicitly create a Future or Task objects if there is no running event loop and no explicit loop argument is passed: ensure_future(), wrap_future(), gather(), shield(), as_completed() and constructors of Future, Task, StreamReader, StreamReaderProtocol.

  • bpo-18369: Certificate and PrivateKey classes were added to the ssl module. Certificates and keys can now be loaded from memory buffer, too.

  • bpo-41486: Use a new output buffer management code for bz2 / lzma / zlib modules, and add .readall() function to _compression.DecompressReader class. These bring some performance improvements. Patch by Ma Lin.

  • bpo-31870: The ssl.get_server_certificate() function now has a timeout parameter.

  • bpo-41735: Fix thread locks in zlib module may go wrong in rare case. Patch by Ma Lin.

  • bpo-36470: Fix dataclasses with InitVars and replace(). Patch by Claudiu Popa.

  • bpo-40849: Expose X509_V_FLAG_PARTIAL_CHAIN ssl flag

  • bpo-35114: ssl.RAND_status() now returns a boolean value (as documented) instead of 1 or 0.

  • bpo-39906: pathlib.Path.stat() and chmod() now accept a follow_symlinks keyword-only argument for consistency with corresponding functions in the os module.

  • bpo-39899: os.path.expanduser() now refuses to guess Windows home directories if the basename of current user's home directory does not match their username.

    pathlib.Path.expanduser() and home() now consistently raise RuntimeError exception when a home directory cannot be resolved. Previously a KeyError exception could be raised on Windows when the "USERNAME" environment variable was unset.

  • bpo-36076: Added SNI support to ssl.get_server_certificate().

  • bpo-38490: Covariance, Pearson's correlation, and simple linear regression functionality was added to statistics module. Patch by Tymoteusz Wołodźko.

  • bpo-33731: Provide a locale.localize() function, which converts a normalized number string into a locale format.

  • bpo-32745: Fix a regression in the handling of ctypes' ctypes.c_wchar_p type: embedded null characters would cause a ValueError to be raised. Patch by Zackery Spytz.


  • bpo-43987: Add "Annotations Best Practices" document as a new HOWTO.

  • bpo-43977: Document the new Py_TPFLAGS_MAPPING and Py_TPFLAGS_SEQUENCE type flags.

  • bpo-43959: The documentation on the PyContextVar C-API was clarified.

  • bpo-43938: Update dataclasses documentation to express that FrozenInstanceError is derived from AttributeError.

  • bpo-43778: Fix the Sphinx glossary_search extension: create the _static/ sub-directory if it doesn't exist.

  • bpo-43755: Update documentation to reflect that unparenthesized lambda expressions can no longer be the expression part in an if clause in comprehensions and generator expressions since Python 3.9.

  • bpo-43739: Fixing the example code in Doc/extending/extending.rst to declare and initialize the pmodule variable to be of the right type.


  • bpo-43961: Fix test_logging.test_namer_rotator_inheritance() on Windows: use os.replace() rather than os.rename(). Patch by Victor Stinner.

  • bpo-43842: Fix a race condition in the SMTP test of test_logging. Don't close a file descriptor (socket) from a different thread while asyncore.loop() is polling the file descriptor. Patch by Victor Stinner.

  • bpo-43843: test.libregrtest now marks a test as ENV_CHANGED (altered the execution environment) if a thread raises an exception but does not catch it. It sets a hook on threading.excepthook(). Use --fail-env-changed option to mark the test as failed. Patch by Victor Stinner.

  • bpo-43811: Tests multiple OpenSSL versions on GitHub Actions. Use ccache to speed up testing.

  • bpo-43791: OpenSSL 3.0.0: Disable testing of legacy protocols TLS 1.0 and 1.1. Tests are failing with TLSV1_ALERT_INTERNAL_ERROR.


  • bpo-43567: Improved generated code refresh (AST/tokens/opcodes/keywords) on Windows.

  • bpo-43669: Implement PEP 644. Python now requires OpenSSL 1.1.1 or newer.


  • bpo-35306: Adds additional arguments to os.startfile() function.

  • bpo-43538: Avoid raising errors from pathlib.Path.exists() when passed an invalid filename.

  • bpo-38822: Fixed os.stat() failing on inaccessible directories with a trailing slash, rather than falling back to the parent directory's metadata. This implicitly affected os.path.exists() and os.path.isdir().

  • bpo-26227: Fixed decoding of host names in socket.gethostbyaddr() and socket.gethostbyname_ex().

  • bpo-40432: Updated pegen regeneration script on Windows to find and use Python 3.8 or higher. Prior to this, pegen regeneration already required 3.8 or higher, but the script may have used lower versions of Python.

  • bpo-43745: Actually updates Windows release to OpenSSL 1.1.1k. Earlier releases were mislabelled and actually included 1.1.1i again.

  • bpo-43652: Update Tcl and Tk to 8.6.11 in Windows installer.

  • bpo-43492: Upgrade Windows installer to use SQLite 3.35.5.

  • bpo-30555: Fix WindowsConsoleIO errors in the presence of fd redirection. Patch by Segev Finer.


  • bpo-42119: Fix check for macOS SDK paths when building Python. Narrow search to match contents of SDKs, namely only files in /System/Library, /System/IOSSupport, and /usr other than /usr/local. Previously, anything under /System was assumed to be in an SDK which causes problems with the new file system layout in 10.15+ where user file systems may appear to be mounted under /System. Paths in /Library were also incorrectly treated as SDK locations.

  • bpo-43568: Drop support for MACOSX_DEPLOYMENT_TARGET < 10.3

  • bpo-44009: Provide "python3.x-intel64" executable to allow reliably forcing macOS universal2 framework builds to run under Rosetta 2 Intel-64 emulation on Apple Silicon Macs. This can be useful for testing or when universal2 wheels are not yet available.

  • bpo-43851: Build SQLite with SQLITE_OMIT_AUTOINIT on macOS. Patch by Erlend E. Aasland.

  • bpo-43492: Update macOS installer to use SQLite 3.35.4.

  • bpo-42235: Mac/BuildScript/ will now use "--enable-optimizations" and --with-lto when building on macOS 10.15 or later.


  • bpo-37903: Add mouse actions to the shell sidebar. Left click and optional drag selects one or more lines, as with the editor line number sidebar. Right click after selecting raises a context menu with 'copy with prompts'. This zips together prompts from the sidebar with lines from the selected text.

  • bpo-43981: Fix reference leak in test_squeezer. Patch by Pablo Galindo

  • bpo-37892: Indent IDLE Shell input with spaces instead of tabs

  • bpo-43655: IDLE dialog windows are now recognized as dialogs by window managers on macOS and X Window.

  • bpo-37903: IDLE's shell now shows prompts in a separate side-bar.


  • bpo-43916: Add a new Py_TPFLAGS_DISALLOW_INSTANTIATION type flag to disallow creating type instances. Patch by Victor Stinner.

  • bpo-43774: Remove the now unused PYMALLOC_DEBUG macro. Debug hooks on memory allocators are now installed by default if Python is built in debug mode (if Py_DEBUG macro is defined). Moreover, they can now be used on Python build in release mode (ex: using PYTHONMALLOC=debug environment variable).

  • bpo-43962: _PyInterpreterState_IDIncref() now calls _PyInterpreterState_IDInitref() and always increments id_refcount. Previously, calling _xxsubinterpreters.get_current() could create an id_refcount inconsistency when a _xxsubinterpreters.InterpreterID object was deallocated. Patch by Victor Stinner.

  • bpo-28254: Add new C-API functions to control the state of the garbage collector: PyGC_Enable(), PyGC_Disable(), PyGC_IsEnabled(), corresponding to the functions in the gc module.

  • bpo-43908: Introduce Py_TPFLAGS_IMMUTABLETYPE flag for immutable type objects, and modify PyType_Ready() to set it for static types. Patch by Erlend E. Aasland.

  • bpo-43795: PyMem_Calloc() is now available in the limited C API (Py_LIMITED_API).

  • bpo-43868: PyOS_ReadlineFunctionPointer() is no longer exported by limited C API headers and by python3.dll on Windows. Like any function that takes FILE*, it is not part of the stable ABI.

  • bpo-43795: Stable ABI and limited API definitions are generated from a central manifest (PEP 652).

  • bpo-43753: Add the Py_Is(x, y) function to test if the x object is the y object, the same as x is y in Python. Add also the Py_IsNone(), Py_IsTrue(), Py_IsFalse() functions to test if an object is, respectively, the None singleton, the True singleton or the False singleton. Patch by Victor Stinner.

Python 3.10.0 alpha 7

Release date: 2021-04-05


  • bpo-42988: CVE-2021-3426: Remove the getfile feature of the pydoc module which could be abused to read arbitrary files on the disk (directory traversal vulnerability). Moreover, even source code of Python modules can contain sensitive data like passwords. Vulnerability reported by David Schwörer.

  • bpo-43285: ftplib no longer trusts the IP address value returned from the server in response to the PASV command by default. This prevents a malicious FTP server from using the response to probe IPv4 address and port combinations on the client network.

    Code that requires the former vulnerable behavior may set a trust_server_pasv_ipv4_address attribute on their ftplib.FTP instances to True to re-enable it.

  • bpo-43439: Add audit hooks for gc.get_objects(), gc.get_referrers() and gc.get_referents(). Patch by Pablo Galindo.

Core and Builtins

  • bpo-27129: Update CPython bytecode magic number.

  • bpo-43672: Raise ImportWarning when calling find_loader().

  • bpo-43660: Fix crash that happens when replacing sys.stderr with a callable that can remove the object while an exception is being printed. Patch by Pablo Galindo.

  • bpo-27129: The bytecode interpreter uses instruction, rather byte, offsets internally. This reduces the number of EXTENDED_ARG instructions needed and streamlines instruction dispatch a bit.

  • bpo-40645: Fix reference leak in the _hashopenssl extension. Patch by Pablo Galindo.

  • bpo-42134: Calls to find_module() by the import system now raise ImportWarning.

  • bpo-41064: Improve the syntax error for invalid usage of double starred elements ('**') in f-strings. Patch by Pablo Galindo.

  • bpo-43575: Speed up calls to map() by using the PEP 590 vectorcall calling convention. Patch by Dong-hee Na.

  • bpo-42137: The import system now prefers using __spec__ for ModuleType.__repr__ over module_repr().

  • bpo-43452: Added micro-optimizations to _PyType_Lookup() to improve cache lookup performance in the common case of cache hits.

  • bpo-43555: Report the column offset for SyntaxError for invalid line continuation characters. Patch by Pablo Galindo.

  • bpo-43517: Fix misdetection of circular imports when using from pkg.mod import attr, which caused false positives in non-trivial multi-threaded code.

  • bpo-43497: Emit SyntaxWarnings for assertions with tuple constants, this is a regression introduced in python3.7

  • bpo-39316: Tracing now has correct line numbers for attribute accesses when the the attribute is on a different line from the object. Improves debugging and profiling for multi-line method chains.

  • bpo-35883: Python no longer fails at startup with a fatal error if a command line argument contains an invalid Unicode character. The Py_DecodeLocale() function now escapes byte sequences which would be decoded as Unicode characters outside the [U+0000; U+10ffff] range.

  • bpo-43410: Fix a bug that was causing the parser to crash when emitting syntax errors when reading input from stdin. Patch by Pablo Galindo

  • bpo-43406: Fix a possible race condition where PyErr_CheckSignals tries to execute a non-Python signal handler.

  • bpo-42128: Add __match_args__ to structsequence based classes. Patch by Pablo Galindo.

  • bpo-43390: CPython now sets the SA_ONSTACK flag in PyOS_setsig for the VM's default signal handlers. This is friendlier to other in-process code that an extension module or embedding use could pull in (such as Golang's cgo) where tiny thread stacks are the norm and sigaltstack() has been used to provide for signal handlers. This is a no-op change for the vast majority of processes that don't use sigaltstack.

  • bpo-43287: Speed up calls to filter() by using the PEP 590 vectorcall calling convention. Patch by Dong-hee Na.

  • bpo-37448: Add a radix tree based memory map to track in-use obmalloc arenas. Use to replace the old implementation of address_in_range(). The radix tree approach makes it easy to increase pool sizes beyond the OS page size. Boosting the pool and arena size allows obmalloc to handle a significantly higher percentage of requests from its ultra-fast paths.

    It also has the advantage of eliminating the memory unsanitary behavior of the previous address_in_range(). The old address_in_range() was marked with the annotations _Py_NO_SANITIZE_ADDRESS, _Py_NO_SANITIZE_THREAD, and _Py_NO_SANITIZE_MEMORY. Those annotations are no longer needed.

    To disable the radix tree map, set a preprocessor flag as follows: -DWITH_PYMALLOC_RADIX_TREE=0.

    Co-authored-by: Tim Peters <>

  • bpo-29988: Only handle asynchronous exceptions and requests to drop the GIL when returning from a call or on the back edges of loops. Makes sure that __exit__() is always called in with statements, even for interrupts.


  • bpo-43720: Document various stdlib deprecations in imp, pkgutil, and importlib.util for removal in Python 3.12.

  • bpo-43433: xmlrpc.client.ServerProxy no longer ignores query and fragment in the URL of the server.

  • bpo-31956: The index() method of array.array now has optional start and stop parameters.

  • bpo-40066: Enum: adjust repr() to show only enum and member name (not value, nor angle brackets) and str() to show only member name. Update and improve documentation to match.

  • bpo-42136: Deprecate all module_repr() methods found in importlib as their use is being phased out by Python 3.12.

  • bpo-35930: Raising an exception raised in a "future" instance will create reference cycles.

  • bpo-41369: Finish updating the vendored libmpdec to version 2.5.1. Patch by Stefan Krah.

  • bpo-43422: Revert the _decimal C API which was added in bpo-41324.

  • bpo-43577: Fix deadlock when using ssl.SSLContext debug callback with ssl.SSLContext.sni_callback().

  • bpo-43571: It's now possible to create MPTCP sockets with IPPROTO_MPTCP

  • bpo-43542: image/heic and image/heif were added to mimetypes.

  • bpo-40645: The hmac module now uses OpenSSL's HMAC implementation when digestmod argument is a hash name or builtin hash function.

  • bpo-43510: Implement PEP 597: Add EncodingWarning warning, -X warn_default_encoding option, PYTHONWARNDEFAULTENCODING environment variable and encoding="locale" argument value.

  • bpo-43521: ast.unparse can now render NaNs and empty sets.

  • bpo-42914: pprint.pprint() gains a new boolean underscore_numbers optional argument to emit integers with thousands separated by an underscore character for improved readability (for example 1_000_000 instead of 1000000).

  • bpo-41361: rotate() calls are now slightly faster due to faster argument parsing.

  • bpo-43423: subprocess.communicate() no longer raises an IndexError when there is an empty stdout or stderr IO buffer during a timeout on Windows.

  • bpo-27820: Fixed long-standing bug of smtplib.SMTP where doing AUTH LOGIN with initial_response_ok=False will fail.

    The cause is that SMTP.auth_login _always_ returns a password if provided with a challenge string, thus non-compliant with the standard for AUTH LOGIN.

    Also fixes bug with the test for smtpd.

  • bpo-43445: Add frozen modules to sys.stdlib_module_names. For example, add "_frozen_importlib" and "_frozen_importlib_external" names.

  • bpo-43245: Add keyword arguments support to ChainMap.new_child().

  • bpo-29982: Add optional parameter ignore_cleanup_errors to tempfile.TemporaryDirectory() and allow multiple cleanup() attempts. Contributed by C.A.M. Gerlach.

  • bpo-43428: Include changes from importlib_metadata 3.7:

    Performance enhancements to distribution discovery.

    entry_points only returns unique distributions.

    Introduces new EntryPoints object for containing a set of entry points with convenience methods for selecting entry points by group or name. entry_points now returns this object if selection parameters are supplied but continues to return a dict object for compatibility. Users are encouraged to rely on the selection interface. The dict object result is likely to be deprecated in the future.

    Added packages_distributions function to return a mapping of packages to the distributions that provide them.

  • bpo-43332: Improves the networking efficiency of http.client when using a proxy via set_tunnel(). Fewer small send calls are made during connection setup.

  • bpo-43420: Improve performance of fractions.Fraction arithmetics for large components. Contributed by Sergey B. Kirpichev.

  • bpo-43356: Allow passing a signal number to _thread.interrupt_main().

  • bpo-43399: Fix ElementTree.extend not working on iterators when using the Python implementation

  • bpo-43369: Improve sqlite3 error handling: If sqlite3_column_text() and sqlite3_column_blob() set SQLITE_NOMEM, MemoryError is now raised. Patch by Erlend E. Aasland.

  • bpo-43368: Fix a regression introduced in GH-24562, where an empty bytestring was fetched as None instead of b'' in sqlite3. Patch by Mariusz Felisiak.

  • bpo-41282: Fixed stacklevel of DeprecationWarning emitted from import distutils.

  • bpo-42129: importlib.resources now honors namespace packages, merging resources from each location in the namespace as introduced in importlib_resources 3.2 and including incidental changes through 5.0.3.

  • bpo-43295: datetime.datetime.strptime() now raises ValueError instead of IndexError when matching 'z' with the %z format specifier.

  • bpo-43125: Return empty string if base64mime.body_encode receive empty bytes

  • bpo-43084: curses.window.enclose() returns now True or False (as was documented) instead of 1 or 0.

  • bpo-42994: Add MIME types for opus, AAC, 3gpp and 3gpp2

  • bpo-14678: Add an invalidate_caches() method to the zipimport.zipimporter class to support importlib.invalidate_caches(). Patch by Desmond Cheong.

  • bpo-42782: Fail fast in shutil.move() to avoid creating destination directories on failure.

  • bpo-40066: Enum's repr() and str() have changed: repr() is now EnumClass.MemberName and str() is MemberName. Additionally, stdlib Enum's whose contents are available as module attributes, such as RegexFlag.IGNORECASE, have their repr() as, e.g. re.IGNORECASE.

  • bpo-26053: Fixed bug where the pdb interactive run command echoed the args from the shell command line, even if those have been overridden at the pdb prompt.

  • bpo-24160: Fixed bug where breakpoints did not persist across multiple debugger sessions in pdb's interactive mode.

  • bpo-40701: When the tempfile.tempdir global variable is set to a value of type bytes, it is now handled consistently. Previously exceptions could be raised from some tempfile APIs when the directory did not already exist in this situation. Also ensures that the tempfile.gettempdir() and tempfile.gettempdirb() functions always return str and bytes respectively.

  • bpo-39342: Expose X509_V_FLAG_ALLOW_PROXY_CERTS as VERIFY_ALLOW_PROXY_CERTS to allow proxy certificate validation as explained in

  • bpo-31861: Add builtins.aiter and builtins.anext. Patch by Joshua Bronson (@jab), Daniel Pope (@lordmauve), and Justin Wang (@justin39).



  • bpo-37945: Fix test_getsetlocale_issue1813() of test_locale: skip the test if setlocale() fails. Patch by Victor Stinner.

  • bpo-41561: Add workaround for Ubuntu's custom OpenSSL security level policy.


  • bpo-43179: Introduce and correctly use ALIGNOF_X in place of SIZEOF_X for alignment-related code in optimized string routines. Patch by Jessica Clarke.

  • bpo-43631: Update macOS, Windows, and CI to OpenSSL 1.1.1k.

  • bpo-43617: Improve Check for presence of autoconf-archive package and remove our copies of M4 macros.

  • bpo-43466: The configure script now supports --with-openssl-rpath option.

  • bpo-43372: Use _freeze_importlib to generate code for the __hello__ module. This approach ensures the code matches the interpreter version. Previously, PYTHON_FOR_REGEN was used to generate the code, which might be wrong. The marshal format for code objects has changed with bpo-42246, commit 877df851. Update the code and the expected code sizes in ctypes test_frozentable.


  • bpo-43440: Build sqlite3 with the R*Tree module enabled. Patch by Erlend E. Aasland.


  • bpo-42225: Document that IDLE can fail on Unix either from misconfigured IP masquerage rules or failure displaying complex colored (non-ascii) characters.


  • bpo-43688: The limited C API is now supported if Python is built in debug mode (if the Py_DEBUG macro is defined). In the limited C API, the Py_INCREF() and Py_DECREF() functions are now implemented as opaque function calls, rather than accessing directly the PyObject.ob_refcnt member, if Python is built in debug mode and the Py_LIMITED_API macro targets Python 3.10 or newer. It became possible to support the limited C API in debug mode because the PyObject structure is the same in release and debug mode since Python 3.8 (see bpo-36465).

    The limited C API is still not supported in the --with-trace-refs special build (Py_TRACE_REFS macro).

    Patch by Victor Stinner.

  • bpo-43244: Remove the pyarena.h header file with functions:

    • PyArena_New()

    • PyArena_Free()

    • PyArena_Malloc()

    • PyArena_AddPyObject()

    These functions were undocumented, excluded from the limited C API, and were only used internally by the compiler. Patch by Victor Stinner.

  • bpo-43244: Remove the compiler and parser functions using struct _mod type, because the public AST C API was removed:

    • PyAST_Compile()

    • PyAST_CompileEx()

    • PyAST_CompileObject()

    • PyFuture_FromAST()

    • PyFuture_FromASTObject()

    • PyParser_ASTFromFile()

    • PyParser_ASTFromFileObject()

    • PyParser_ASTFromFilename()

    • PyParser_ASTFromString()

    • PyParser_ASTFromStringObject()

    These functions were undocumented and excluded from the limited C API. Patch by Victor Stinner.

  • bpo-43244: Remove ast.h, asdl.h, and Python-ast.h header files. These functions were undocumented and excluded from the limited C API. Most names defined by these header files were not prefixed by Py and so could create names conflicts. For example, Python-ast.h defined a Yield macro which was conflict with the Yield name used by the Windows <winbase.h> header. Use the Python ast module instead. Patch by Victor Stinner.

  • bpo-43541: Fix a PyEval_EvalCodeEx() regression: fix reference counting on builtins. Patch by Victor Stinner.

  • bpo-43244: Remove the symtable.h header file and the undocumented functions:

    • PyST_GetScope()

    • PySymtable_Build()

    • PySymtable_BuildObject()

    • PySymtable_Free()

    • Py_SymtableString()

    • Py_SymtableStringObject()

    The Py_SymtableString() function was part the stable ABI by mistake but it could not be used, because the symtable.h header file was excluded from the limited C API.

    The Python symtable module remains available and is unchanged.

    Patch by Victor Stinner.

  • bpo-43244: Remove the PyAST_Validate() function. It is no longer possible to build a AST object (mod_ty type) with the public C API. The function was already excluded from the limited C API (PEP 384). Patch by Victor Stinner.

Python 3.10.0 alpha 6

Release date: 2021-03-01


  • bpo-42967: Fix web cache poisoning vulnerability by defaulting the query args separator to &, and allowing the user to choose a custom separator.

Core and Builtins

  • bpo-43321: Fix SystemError raised when PyArg_Parse*() is used with # but without PY_SSIZE_T_CLEAN defined.

  • bpo-36346: PyArg_Parse*() functions now emits DeprecationWarning when u or Z format is used. See PEP 623 for detail.

  • bpo-43277: Add a new PySet_CheckExact() function to the C-API to check if an object is an instance of set but not an instance of a subtype. Patch by Pablo Galindo.

  • bpo-42990: The types.FunctionType constructor now inherits the current builtins if the globals dictionary has no "__builtins__" key, rather than using {"None": None} as builtins: same behavior as eval() and exec() functions. Defining a function with def function(...): ... in Python is not affected, globals cannot be overridden with this syntax: it also inherits the current builtins. Patch by Victor Stinner.

  • bpo-42990: Functions have a new __builtins__ attribute which is used to look for builtin symbols when a function is executed, instead of looking into __globals__['__builtins__']. Patch by Mark Shannon and Victor Stinner.

  • bpo-43149: Improve the error message in the parser for exception groups without parentheses. Patch by Pablo Galindo.

  • bpo-43121: Fixed an incorrect SyntaxError message for missing comma in literals. Patch by Pablo Galindo.

  • bpo-42819: readline: Explicitly disable bracketed paste in the interactive interpreter, even if it's set in the inputrc, is enabled by default (eg GNU Readline 8.1), or a user calls readline.read_init_file(). The Python REPL has not implemented bracketed paste support. Also, bracketed mode writes the "\x1b[?2004h" escape sequence into stdout which causes test failures in applications that don't support it. It can still be explicitly enabled by calling readline.parse_and_bind("set enable-bracketed-paste on"). Patch by Dustin Rodrigues.

  • bpo-42808: Simple calls to type(object) are now faster due to the vectorcall calling convention. Patch by Dennis Sweeney.

  • bpo-42217: Make the compiler merges same co_code and co_linetable objects in a module like already did for co_consts.

  • bpo-41972: Substring search functions such as str1 in str2 and str2.find(str1) now sometimes use the "Two-Way" string comparison algorithm to avoid quadratic behavior on long strings.

  • bpo-42128: Implement PEP 634 (structural pattern matching). Patch by Brandt Bucher.

  • bpo-40692: In the concurrent.futures.ProcessPoolExecutor, validate that multiprocess.synchronize() is available on a given platform and rely on that check in the concurrent.futures test suite so we can run tests that are unrelated to ProcessPoolExecutor on those platforms.

  • bpo-38302: If object.__ipow__() returns NotImplemented, the operator will correctly fall back to object.__pow__() and object.__rpow__() as expected.


  • bpo-43316: The python -m gzip command line application now properly fails when detecting an unsupported extension. It exits with a non-zero exit code and prints an error message to stderr.

  • bpo-43317: Set the chunk size for the gzip module main function to io.DEFAULT_BUFFER_SIZE. This is slightly faster than the 1024 bytes constant that was used previously.

  • bpo-43146: Handle None in single-arg versions of print_exception() and format_exception().

  • bpo-43260: Fix TextIOWrapper can not flush internal buffer forever after very large text is written.

  • bpo-43258: Prevent needless allocation of sqlite3 aggregate function context when no rows match an aggregate query. Patch by Erlend E. Aasland.

  • bpo-43251: Improve sqlite3 error handling: sqlite3_column_name() failures now result in MemoryError. Patch by Erlend E. Aasland.

  • bpo-40956: Fix segfault in sqlite3.Connection.backup() if no argument was provided. The regression was introduced by GH-23838. Patch by Erlend E. Aasland.

  • bpo-43172: The readline module now passes its tests when built directly against libedit. Existing irreconcilable API differences remain in readline.get_begidx() and readline.get_endidx() behavior based on libreadline vs libedit use.

  • bpo-43163: Fix a bug in codeop that was causing it to not ask for more input when multi-line snippets have unclosed parentheses. Patch by Pablo Galindo

  • bpo-43162: deprecate unsupported ability to access enum members as attributes of other enum members

  • bpo-43146: Fix recent regression in None argument handling in traceback module functions.

  • bpo-43102: The namedtuple __new__ method had its __builtins__ set to None instead of an actual dictionary. This created problems for introspection tools.

  • bpo-43106: Added O_EVTONLY, O_FSYNC, O_SYMLINK and O_NOFOLLOW_ANY for macOS. Patch by Dong-hee Na.

  • bpo-42960: Adds resource.RLIMIT_KQUEUES constant from FreeBSD to the resource module.

  • bpo-42151: Make the pure Python implementation of xml.etree.ElementTree behave the same as the C implementation (_elementree) regarding default attribute values (by not setting specified_attributes=1).

  • bpo-29753: In ctypes, now packed bitfields are calculated properly and the first item of packed bitfields is now shrank correctly.


  • bpo-27646: Clarify that 'yield from <expr>' works with any iterable, not just iterators.

  • bpo-36346: Update some deprecated unicode APIs which are documented as "will be removed in 4.0" to "3.12". See PEP 623 for detail.


  • bpo-43288: Fix test_importlib to correctly skip Unicode file tests if the filesystem does not support them.


  • bpo-43174: Windows build now uses /utf-8 compiler option.

  • bpo-43103: Add a new configure --without-static-libpython option to not build the libpythonMAJOR.MINOR.a static library and not install the python.o object file.

  • bpo-13501: The configure script can now use libedit instead of readline with the command line option --with-readline=editline.

  • bpo-42603: Make configure script use pkg-config to detect the location of Tcl/Tk headers and libraries, used to build tkinter.

    On macOS, a Tcl/Tk configuration provided by pkg-config will be preferred over Tcl/Tk frameworks installed in /{System/,}Library/Frameworks. If both exist and the latter is preferred, the appropriate --with-tcltk-* configuration options need to be explicitly set.

  • bpo-39448: Add the "regen-frozen" makefile target that regenerates the code for the frozen __hello__ module.


  • bpo-43155: PyCMethod_New() is now present in python3.lib.


  • bpo-41837: Update macOS installer build to use OpenSSL 1.1.1j.


  • bpo-43283: Document why printing to IDLE's Shell is often slower than printing to a system terminal and that it can be made faster by pre-formatting a single string before printing.


  • bpo-43278: Always put compiler and system information on the first line of the REPL welcome message.

  • bpo-43270: Remove the private _PyErr_OCCURRED() macro: use the public PyErr_Occurred() function instead.

  • bpo-35134: Move odictobject.h, parser_interface.h, picklebufobject.h, pydebug.h, and pyfpe.h into the cpython/ directory. They must not be included directly, as they are already included by Python.h: Include Files.

  • bpo-35134: Move pyarena.h, pyctype.h, and pytime.h into the cpython/ directory. They must not be included directly, as they are already included by Python.h: Include Files.

  • bpo-40170: PyExceptionClass_Name() is now always declared as a function, in order to hide implementation details. The macro accessed PyTypeObject.tp_name directly. Patch by Erlend E. Aasland.

  • bpo-43239: The PyCFunction_New() function is now exported in the ABI when compiled with -fvisibility=hidden.

  • bpo-40170: PyIter_Check() is now always declared as a function, in order to hide implementation details. The macro accessed PyTypeObject.tp_iternext directly. Patch by Erlend E. Aasland.

  • bpo-40170: Convert PyDescr_IsData() macro to a function to hide implementation details: The macro accessed PyTypeObject.tp_descr_set directly. Patch by Erlend E. Aasland.

  • bpo-43181: Convert PyObject_TypeCheck() macro to a static inline function. Patch by Erlend E. Aasland.

Python 3.10.0 alpha 5

Release date: 2021-02-02


Core and Builtins

  • bpo-42990: Refactor the PyEval_ family of functions.

    • An new function _PyEval_Vector is added to simplify calls to Python from C.

    • _PyEval_EvalCodeWithName is removed

    • PyEval_EvalCodeEx is retained as part of the API, but is not used internally

  • bpo-38631: Replace Py_FatalError() calls in the compiler with regular SystemError exceptions. Patch by Victor Stinner.

  • bpo-42997: Improve error message for missing ":" before blocks. Patch by Pablo Galindo.

  • bpo-43017: Improve error message in the parser when using un-parenthesised tuples in comprehensions. Patch by Pablo Galindo.

  • bpo-42986: Fix parser crash when reporting syntax errors in f-string with newlines. Patch by Pablo Galindo.

  • bpo-40176: Syntax errors for unterminated string literals now point to the start of the string instead of reporting EOF/EOL.

  • bpo-42927: The inline cache for LOAD_ATTR now also optimizes access to attributes defined by __slots__. This makes reading such attribute up to 30% faster.

  • bpo-42864: Improve error messages in the parser when parentheses are not closed. Patch by Pablo Galindo.

  • bpo-42924: Fix bytearray repetition incorrectly copying data from the start of the buffer, even if the data is offset within the buffer (e.g. after reassigning a slice at the start of the bytearray to a shorter byte string).

  • bpo-42882: Fix the _PyUnicode_FromId() function (_Py_IDENTIFIER(var) API) when Py_Initialize() / Py_Finalize() is called multiple times: preserve _PyRuntime.unicode_ids.next_index value.

  • bpo-42827: Fix a crash when working out the error line of a SyntaxError in some multi-line expressions.

  • bpo-42823: frame.f_lineno is correct even if frame.f_trace is set to True

  • bpo-37324: Remove deprecated aliases to Classes de base abstraites de collections from the collections module.

  • bpo-41994: Fixed possible leak in import when sys.modules is not a dict.

  • bpo-27772: In string formatting, preceding the width field by '0' no longer affects the default alignment for strings.


  • bpo-43108: Fixed a reference leak in the curses module. Patch by Pablo Galindo

  • bpo-43077: Update the bundled pip to 21.0.1 and setuptools to 52.0.0.

  • bpo-41282: Deprecate distutils in documentation and add warning on import.

  • bpo-43014: Improve performance of tokenize by 20-30%. Patch by Anthony Sottile.

  • bpo-42323: Fix math.nextafter() for NaN on AIX.

  • bpo-42955: Add sys.stdlib_module_names, containing the list of the standard library module names. Patch by Victor Stinner.

  • bpo-42944: Fix random.Random.sample when counts argument is not None.

  • bpo-42934: Use TracebackException's new compact param in TestResult to reduce time and memory consumed by traceback formatting.

  • bpo-42931: Add randbytes() to random.__all__.

  • bpo-38250: [Enum] Flags consisting of a single bit are now considered canonical, and will be the only flags returned from listing and iterating over a Flag class or a Flag member. Multi-bit flags are considered aliases; they will be returned from lookups and operations that result in their value. Iteration for both Flag and Flag members is in definition order.

  • bpo-42877: Added the compact parameter to the constructor of traceback.TracebackException to reduce time and memory for use cases that only need to call TracebackException.format() and TracebackException.format_exception_only().

  • bpo-42923: The Py_FatalError() function and the faulthandler module now dump the list of extension modules on a fatal error.

  • bpo-42848: Removed recursion from TracebackException to allow it to handle long exception chains.

  • bpo-42901: [Enum] move member creation from EnumMeta.__new__ to _proto_member.__set_name__, allowing members to be created and visible in __init_subclass__.

  • bpo-42780: Fix os.set_inheritable() for O_PATH file descriptors on Linux.

  • bpo-42866: Fix a reference leak in the getcodec() function of CJK codecs. Patch by Victor Stinner.

  • bpo-42846: Convert the 6 CJK codec extension modules (_codecs_cn, _codecs_hk, _codecs_iso2022, _codecs_jp, _codecs_kr and _codecs_tw) to the multiphase initialization API (PEP 489). Patch by Victor Stinner.

  • bpo-42851: remove __init_subclass__ support for Enum members

  • bpo-42834: Make internal caches of the _json module compatible with subinterpreters.

  • bpo-41748: Fix HTMLParser parsing rules for element attributes containing commas with spaces. Patch by Karl Dubost.

  • bpo-40810: Require SQLite 3.7.15 or newer. Patch by Erlend E. Aasland.

  • bpo-1635741: Convert the _multibytecodec extension module (CJK codecs) to multi-phase initialization (PEP 489). Patch by Erlend E. Aasland.

  • bpo-42802: The distutils bdist_wininst command deprecated in Python 3.8 has been removed. The distutils bdist_wheel command is now recommended to distribute binary packages on Windows.

  • bpo-24464: The undocumented built-in function sqlite3.enable_shared_cache is now deprecated, scheduled for removal in Python 3.12. Its use is strongly discouraged by the SQLite3 documentation. Patch by Erlend E. Aasland.

  • bpo-42384: Make pdb populate sys.path[0] exactly the same as regular python execution.

  • bpo-42383: Fix pdb: previously pdb would fail to restart the debugging target if it was specified using a relative path and the current directory changed.

  • bpo-42005: Fix CLI of cProfile and profile to catch BrokenPipeError.

  • bpo-41604: Don't decrement the reference count of the previous user_ptr when set_panel_userptr fails.

  • bpo-41149: Allow executing callables that have a boolean value of False when passed to Threading.thread as the target. Patch contributed by Barney Stratford.

  • bpo-38307: Add an 'end_lineno' attribute to the Class and Function objects that appear in the tree returned by pyclbr functions. This and the existing 'lineno' attribute define the extent of class and def statements. Patch by Aviral Srivastava.

  • bpo-39273: The BUTTON5_* constants are now exposed in the curses module if available.

  • bpo-33289: Correct call to tkinter.colorchooser to return RGB triplet of ints instead of floats. Patch by Cheryl Sabella.


  • bpo-40304: Fix doc for type(name, bases, dict). Patch by Boris Verkhovskiy and Éric Araujo.

  • bpo-42811: Updated importlib.utils.resolve_name() doc to use __spec__.parent instead of __package__. (Thanks Yair Frid.)


  • bpo-40823: Use unittest.TestLoader().loadTestsFromTestCase() instead of unittest.makeSuite() in sqlite3 tests. Patch by Erlend E. Aasland.

  • bpo-40810: In sqlite3, fix CheckTraceCallbackContent for SQLite pre 3.7.15.


  • bpo-43031: Pass --timeout=$(TESTTIMEOUT) option to the default profile task ./python -m test --pgo command.

  • bpo-36143: make regen-all now also runs regen-keyword. Patch by Victor Stinner.

  • bpo-42874: Removed the grep -q and -E flags in the tzpath validation section of the configure script to better accommodate users of some platforms (specifically Solaris 10).

  • bpo-31904: Add library search path by wr-cc in add_cross_compiling_paths() for VxWorks.

  • bpo-42856: Add --with-wheel-pkg-dir=PATH option to the ./configure script. If specified, the ensurepip module looks for setuptools and pip wheel packages in this directory: if both are present, these wheel packages are used instead of ensurepip bundled wheel packages.

    Some Linux distribution packaging policies recommend against bundling dependencies. For example, Fedora installs wheel packages in the /usr/share/python-wheels/ directory and don't install the ensurepip._bundled package.


  • bpo-41837: Updated Windows installer to include OpenSSL 1.1.1i

  • bpo-42584: Upgrade Windows installer to use SQLite 3.34.0.


  • bpo-42504: Ensure that the value of sysconfig.get_config_var('MACOSX_DEPLOYMENT_TARGET') is always a string, even in when the value is parsable as an integer.


  • bpo-43008: Make IDLE invoke sys.excepthook() in normal, 2-process mode. Patch by Ken Hilton.

  • bpo-33065: Fix problem debugging user classes with __repr__ method.

  • bpo-23544: Disable Debug=>Stack Viewer when user code is running or Debugger is active, to prevent hang or crash. Patch by Zackery Spytz.

  • bpo-32631: Finish zzdummy example extension module: make menu entries work; add docstrings and tests with 100% coverage.


  • bpo-42979: When Python is built in debug mode (with C assertions), calling a type slot like sq_length (__len__() in Python) now fails with a fatal error if the slot succeeded with an exception set, or failed with no exception set. The error message contains the slot, the type name, and the current exception (if an exception is set). Patch by Victor Stinner.

  • bpo-43030: Fixed a compiler warning in Py_UNICODE_ISSPACE() on platforms with signed wchar_t.

Python 3.10.0 alpha 4

Release date: 2021-01-04

Core and Builtins

  • bpo-42814: Fix undefined behavior in Objects/genericaliasobject.c.

  • bpo-42806: Fix the column offsets for f-strings ast nodes surrounded by parentheses and for nodes that spawn multiple lines. Patch by Pablo Galindo.

  • bpo-40631: Fix regression where a single parenthesized starred expression was a valid assignment target.

  • bpo-27794: Improve the error message for failed writes/deletes to property objects. When possible, the attribute name is now shown. Patch provided by Yurii Karabas.

  • bpo-42745: Make the type attribute lookup cache per-interpreter. Patch by Victor Stinner.

  • bpo-42246: Jumps to jumps are not eliminated when it would break PEP 626.

  • bpo-42246: Make sure that the f_lasti and f_lineno attributes of a frame are set correctly when an exception is raised or re-raised. Required for PEP 626.

  • bpo-32381: The coding cookie (ex: # coding: latin1) is now ignored in the command passed to the -c command line option. Patch by Victor Stinner.

  • bpo-30858: Improve error location in expressions that contain assignments. Patch by Pablo Galindo and Lysandros Nikolaou.

  • bpo-42615: Remove jump commands made redundant by the deletion of unreachable bytecode blocks

  • bpo-42639: Make the atexit module state per-interpreter. It is now safe have more than one atexit module instance. Patch by Dong-hee Na and Victor Stinner.

  • bpo-32381: Fix encoding name when running a .pyc file on Windows: PyRun_SimpleFileExFlags() now uses the correct encoding to decode the filename.

  • bpo-42195: The __args__ of the parameterized generics for typing.Callable and are now consistent. The __args__ for are now flattened while typing.Callable's have not changed. To allow this change, types.GenericAlias can now be subclassed and's __class_getitem__ will now return a subclass of types.GenericAlias. Tests for typing were also updated to not subclass things like Callable[..., T] as that is not a valid base class. Finally, both Callables no longer validate their argtypes, in Callable[[argtypes], resulttype] to prepare for PEP 612. Patch by Ken Jin.

  • bpo-40137: Convert functools module to use PyType_FromModuleAndSpec().

  • bpo-40077: Convert array to use heap types, and establish module state for these.

  • bpo-42008: Fix _random.Random() seeding.

  • bpo-1635741: Port the pyexpat extension module to multi-phase initialization (PEP 489).

  • bpo-40521: Make the Unicode dictionary of interned strings compatible with subinterpreters. Patch by Victor Stinner.

  • bpo-39465: Make _PyUnicode_FromId() function compatible with subinterpreters. Each interpreter now has an array of identifier objects (interned strings decoded from UTF-8). Patch by Victor Stinner.


  • bpo-42257: Handle empty string in variable executable in platform.libc_ver()

  • bpo-42772: randrange() now raises a TypeError when step is specified without a stop argument. Formerly, it silently ignored the step argument.

  • bpo-42759: Fixed equality comparison of tkinter.Variable and tkinter.font.Font. Objects which belong to different Tcl interpreters are now always different, even if they have the same name.

  • bpo-42756: Configure LMTP Unix-domain socket to use socket global default timeout when a timeout is not explicitly provided.

  • bpo-23328: Allow / character in username, password fields on _PROXY envars.

  • bpo-42740: typing.get_args() and typing.get_origin() now support PEP 604 union types and PEP 612 additions to Callable.

  • bpo-42655: subprocess extra_groups is now correctly passed into setgroups() system call.

  • bpo-42727: EnumMeta.__prepare__ now accepts **kwds to properly support __init_subclass__

  • bpo-38308: Add optional weights to statistics.harmonic_mean().

  • bpo-42721: When simple query dialogs (tkinter.simpledialog), message boxes (tkinter.messagebox) or color choose dialog (tkinter.colorchooser) are created without arguments master and parent, and the default root window is not yet created, and NoDefaultRoot() was not called, a new temporal hidden root window will be created automatically. It will not be set as the default root window and will be destroyed right after closing the dialog window. It will help to use these simple dialog windows in programs which do not need other GUI.

  • bpo-25246: Optimized collections.deque.remove().

  • bpo-35728: Added a root parameter to tkinter.font.nametofont().

  • bpo-15303: tkinter supports now widgets with boolean value False.

  • bpo-42681: Fixed range checks for color and pair numbers in curses.

  • bpo-42685: Improved placing of simple query windows in Tkinter (such as tkinter.simpledialog.askinteger()). They are now centered at the center of the parent window if it is specified and shown, otherwise at the center of the screen.

  • bpo-9694: Argparse help no longer uses the confusing phrase, "optional arguments". It uses "options" instead.

  • bpo-1635741: Port the _thread extension module to the multiphase initialization API (PEP 489) and convert its static types to heap types.

  • bpo-37961: Fix crash in tracemalloc.Traceback.__repr__() (regressed in Python 3.9).

  • bpo-42630: tkinter functions and constructors which need a default root window raise now RuntimeError with descriptive message instead of obscure AttributeError or NameError if it is not created yet or cannot be created automatically.

  • bpo-42639: atexit._run_exitfuncs() now logs callback exceptions using sys.unraisablehook, rather than logging them directly into sys.stderr and raise the last exception.

  • bpo-42644: logging.disable will now validate the types and value of its parameter. It also now accepts strings representing the levels (as does loging.setLevel) instead of only the numerical values.

  • bpo-42639: At Python exit, if a callback registered with atexit.register() fails, its exception is now logged. Previously, only some exceptions were logged, and the last exception was always silently ignored.

  • bpo-36541: Fixed lib2to3.pgen2 to be able to parse PEP-570 positional only argument syntax.

  • bpo-42382: In importlib.metadata: - EntryPoint objects now expose a .dist object referencing the Distribution when constructed from a Distribution. - Add support for package discovery under package normalization rules. - The object returned by metadata() now has a formally-defined protocol called PackageMetadata with declared support for the .get_all() method. - Synced with importlib_metadata 3.3.

  • bpo-41877: A check is added against misspellings of autospect, auto_spec and set_spec being passed as arguments to patch, patch.object and create_autospec.

  • bpo-39717: [tarfile] update nested exception raising to use from None or from e

  • bpo-41877: AttributeError for suspected misspellings of assertions on mocks are now pointing out that the cause are misspelled assertions and also what to do if the misspelling is actually an intended attribute name. The unittest.mock document is also updated to reflect the current set of recognised misspellings.

  • bpo-41559: Implemented PEP 612: added ParamSpec and Concatenate to typing. Patch by Ken Jin.

  • bpo-42385: StrEnum: fix _generate_next_value_ to return a str

  • bpo-31904: Define THREAD_STACK_SIZE for VxWorks.

  • bpo-34750: [Enum] _EnumDict.update() is now supported

  • bpo-42517: Enum: private names do not become members / do not generate errors -- they remain normal attributes

  • bpo-42678: Enum: call __init_subclass__ after members have been added

  • bpo-28964: ast.literal_eval() adds line number information (if available) in error message for malformed nodes.

  • bpo-42470: random.sample() no longer warns on a sequence which is also a set.

  • bpo-31904: posixpath.expanduser() returns the input path unchanged if user home directory is None on VxWorks.

  • bpo-42388: Fix subprocess.check_output(..., input=None) behavior when text=True to be consistent with that of the documentation and universal_newlines=True.

  • bpo-34463: Fixed discrepancy between traceback and the interpreter in formatting of SyntaxError with lineno not set (traceback was changed to match interpreter).

  • bpo-42393: Raise OverflowError instead of silent truncation in socket.ntohs() and socket.htons(). Silent truncation was deprecated in Python 3.7. Patch by Erlend E. Aasland

  • bpo-42222: Harmonized random.randrange() argument handling to match range().

    • The integer test and conversion in randrange() now uses operator.index().

    • Non-integer arguments to randrange() are deprecated.

    • The ValueError is deprecated in favor of a TypeError.

    • It now runs a little faster than before.

    (Contributed by Raymond Hettinger and Serhiy Storchaka.)

  • bpo-42163: Restore compatibility for uname_result around deepcopy and _replace.

  • bpo-42090: zipfile.Path.joinpath now accepts arbitrary arguments, same as pathlib.Path.joinpath.

  • bpo-1635741: Port the _csv module to the multi-phase initialization API (PEP 489).

  • bpo-42059: typing.TypedDict types created using the alternative call-style syntax now correctly respect the total keyword argument when setting their __required_keys__ and __optional_keys__ class attributes.

  • bpo-41960: Add globalns and localns parameters to the inspect.signature() and inspect.Signature.from_callable().

  • bpo-41907: fix format() behavior for IntFlag

  • bpo-41891: Ensure asyncio.wait_for waits for task completion

  • bpo-24792: Fixed bug where zipimporter sometimes reports an incorrect cause of import errors.

  • bpo-31904: Fix site and sysconfig modules for VxWorks RTOS which has no home directories.

  • bpo-41462: Add os.set_blocking() support for VxWorks RTOS.

  • bpo-40219: Lowered tkinter.ttk.LabeledScale dummy widget to prevent hiding part of the content label.

  • bpo-37193: Fixed memory leak in socketserver.ThreadingMixIn introduced in Python 3.7.

  • bpo-39068: Fix initialization race condition in a85encode() and b85encode() in base64. Patch by Brandon Stansbury.



  • bpo-42794: Update test_nntplib to use official group name of for testing. Patch by Dong-hee Na.

  • bpo-31904: Skip some asyncio tests on VxWorks.

  • bpo-42641: Enhance test_select.test_select(): it now takes 500 ms rather than 10 seconds. Use Python rather than a shell to make the test more portable.

  • bpo-31904: Skip some tests in _test_all_chown_common() on VxWorks.

  • bpo-42199: Fix bytecode helper assertNotInBytecode.

  • bpo-41443: Add more attribute checking in

  • bpo-31904: Disable os.popen and impacted tests on VxWorks

  • bpo-41439: Port test_ssl and test_uuid to VxWorks RTOS.


  • bpo-42692: Fix __builtin_available check on older compilers. Patch by Joshua Root.

  • bpo-27640: Added --disable-test-modules option to the configure script: don't build nor install test modules. Patch by Xavier de Gaye, Thomas Petazzoni and Peixing Xin.

  • bpo-42604: Now all platforms use a value for the "EXT_SUFFIX" build variable derived from SOABI (for instance in freeBSD, "EXT_SUFFIX" is now "" instead of ".so"). Previously only Linux, Mac and VxWorks were using a value for "EXT_SUFFIX" that included "SOABI".

  • bpo-42598: Fix implicit function declarations in configure which could have resulted in incorrect configuration checks. Patch contributed by Joshua Root.

  • bpo-31904: Enable for VxWorks.

  • bpo-29076: Add fish shell support to macOS installer.


  • bpo-42361: Update macOS installer build to use Tcl/Tk 8.6.11 (rc2, expected to be final release).

  • bpo-41837: Update macOS installer build to use OpenSSL 1.1.1i.

  • bpo-42584: Update macOS installer to use SQLite 3.34.0.


  • bpo-42726: Fixed Python 3 compatibility issue with gdb/ handling of attribute dictionaries.

  • bpo-42613: Fix tool to use the prope config and library directories. Patch by Victor Stinner.


  • bpo-42591: Export the Py_FrozenMain() function: fix a Python 3.9.0 regression. Python 3.9 uses -fvisibility=hidden and the function was not exported explicitly and so not exported.

  • bpo-32381: Remove the private _Py_fopen() function which is no longer needed. Use _Py_wfopen() or _Py_fopen_obj() instead. Patch by Victor Stinner.

  • bpo-1635741: Port resource extension module to module state

  • bpo-42111: Update the xxlimited module to be a better example of how to use the limited C API.

  • bpo-40052: Fix an alignment build warning/error in function PyVectorcall_Function(). Patch by Andreas Schneider, Antoine Pitrou and Petr Viktorin.

Python 3.10.0 alpha 3

Release date: 2020-12-07


  • bpo-40791: Add volatile to the accumulator variable in hmac.compare_digest, making constant-time-defeating optimizations less likely.

Core and Builtins

  • bpo-42576: types.GenericAlias will now raise a TypeError when attempting to initialize with a keyword argument. Previously, this would cause the interpreter to crash if the interpreter was compiled with debug symbols. This does not affect interpreters compiled for release. Patch by Ken Jin.

  • bpo-42536: Several built-in and standard library types now ensure that their internal result tuples are always tracked by the garbage collector:

    Previously, they could have become untracked by a prior garbage collection. Patch by Brandt Bucher.

  • bpo-42500: Improve handling of exceptions near recursion limit. Converts a number of Fatal Errors in RecursionErrors.

  • bpo-42246: PEP 626: After a return, the f_lineno attribute of a frame is always the last line executed.

  • bpo-42435: Speed up comparison of bytes objects with non-bytes objects when option -b is specified. Speed up comparison of bytarray objects with non-buffer object.

  • bpo-1635741: Port the _warnings extension module to the multi-phase initialization API (PEP 489). Patch by Victor Stinner.

  • bpo-41686: On Windows, the SIGINT event, _PyOS_SigintEvent(), is now created even if Python is configured to not install signal handlers (if PyConfig.install_signal_handlers equals to 0, or Py_InitializeEx(0)).

  • bpo-42381: Allow assignment expressions in set literals and set comprehensions as per PEP 572. Patch by Pablo Galindo.

  • bpo-42202: Change function parameters annotations internal representation to tuple of strings. Patch provided by Yurii Karabas.

  • bpo-42374: Fix a regression introduced by the new parser, where an unparenthesized walrus operator was not allowed within generator expressions.

  • bpo-42316: Allow an unparenthesized walrus in subscript indexes.

  • bpo-42349: Make sure that the compiler front-end produces a well-formed control flow graph. Be be more aggressive in the compiler back-end, as it is now safe to do so.

  • bpo-42296: On Windows, fix a regression in signal handling which prevented to interrupt a program using CTRL+C. The signal handler can be run in a thread different than the Python thread, in which case the test deciding if the thread can handle signals is wrong.

  • bpo-42332: types.GenericAlias objects can now be the targets of weakrefs.

  • bpo-42282: Optimise constant subexpressions that appear as part of named expressions (previously the AST optimiser did not descend into named expressions). Patch by Nick Coghlan.

  • bpo-42266: Fixed a bug with the LOAD_ATTR opcode cache that was not respecting monkey-patching a class-level attribute to make it a descriptor. Patch by Pablo Galindo.

  • bpo-40077: Convert queue to use heap types.

  • bpo-42246: Improved accuracy of line tracing events and f_lineno attribute of Frame objects. See PEP 626 for details.

  • bpo-40077: Convert mmap to use heap types.

  • bpo-42233: Allow GenericAlias objects to use union type expressions. This allows expressions like list[int] | dict[float, str] where previously a TypeError would have been thrown. This also fixes union type expressions not de-duplicating GenericAlias objects. (Contributed by Ken Jin in bpo-42233.)

  • bpo-26131: The import system triggers a ImportWarning when it falls back to using load_module().


  • bpo-5054: CGIHTTPRequestHandler.run_cgi() HTTP_ACCEPT improperly parsed. Replace the special purpose getallmatchingheaders with generic get_all method and add relevant tests.

    Original Patch by Martin Panter. Modified by Senthil Kumaran.

  • bpo-42562: Fix issue when dis failed to parse function that has no line numbers. Patch provided by Yurii Karabas.

  • bpo-17735: inspect.findsource() now raises OSError instead of IndexError when co_lineno of a code object is greater than the file length. This can happen, for example, when a file is edited after it was imported. PR by Irit Katriel.

  • bpo-42116: Fix handling of trailing comments by inspect.getsource().

  • bpo-42532: Remove unexpected call of __bool__ when passing a spec_arg argument to a Mock.

  • bpo-38200: Added itertools.pairwise()

  • bpo-41818: Fix test_master_read() so that it succeeds on all platforms that either raise OSError or return b"" upon reading from master.

  • bpo-42487: ChainMap.__iter__ no longer calls __getitem__ on underlying maps

  • bpo-42482: TracebackException no longer holds a reference to the exception's traceback object. Consequently, instances of TracebackException for equivalent but non-equal exceptions now compare as equal.

  • bpo-41818: Make test_openpty() avoid unexpected success due to number of rows and/or number of columns being == 0.

  • bpo-42392: Remove loop parameter from asyncio.subprocess and asyncio.tasks functions. Patch provided by Yurii Karabas.

  • bpo-42392: Remove loop parameter from asyncio.open_connection and asyncio.start_server functions. Patch provided by Yurii Karabas.

  • bpo-28468: Add platform.freedesktop_os_release() function to parse os-release files.

  • bpo-42299: Removed the formatter module, which was deprecated in Python 3.4. It is somewhat obsolete, little used, and not tested. It was originally scheduled to be removed in Python 3.6, but such removals were delayed until after Python 2.7 EOL. Existing users should copy whatever classes they use into their code. Patch by Dong-hee Na and and Terry J. Reedy.

  • bpo-26131: Deprecate zipimport.zipimporter.load_module() in favour of exec_module().

  • bpo-41818: Updated tests for the pty library. test_basic() has been changed to test_openpty(); this additionally checks if slave termios and slave winsize are being set properly by pty.openpty(). In order to add support for FreeBSD, NetBSD, OpenBSD, and Darwin, this also adds test_master_read(), which demonstrates that pty.spawn() should not depend on an OSError to exit from its copy loop.

  • bpo-42392: Remove loop parameter from __init__ in all asyncio.locks and asyncio.Queue classes. Patch provided by Yurii Karabas.

  • bpo-15450: Make filecmp.dircmp respect subclassing. Now the filecmp.dircmp.subdirs behaves as expected when subclassing dircmp.

  • bpo-42413: The exception socket.timeout is now an alias of TimeoutError.

  • bpo-31904: Support signal module on VxWorks.

  • bpo-42406: We fixed an issue in pickle.whichmodule in which importing multiprocessing could change the how pickle identifies which module an object belongs to, potentially breaking the unpickling of those objects.

  • bpo-42403: Simplify the importlib external bootstrap code: importlib._bootstrap_external now uses regular imports to import builtin modules. When it is imported, the builtin __import__() function is already fully working and so can be used to import builtin modules like sys. Patch by Victor Stinner.

  • bpo-1635741: Convert _sre module types to heap types (PEP 384). Patch by Erlend E. Aasland.

  • bpo-42375: subprocess module update for DragonFlyBSD support.

  • bpo-41713: Port the _signal extension module to the multi-phase initialization API (PEP 489). Patch by Victor Stinner and Mohamed Koubaa.

  • bpo-37205: time.time(), time.perf_counter() and time.monotonic() functions can no longer fail with a Python fatal error, instead raise a regular Python exception on failure.

  • bpo-42328: Fixed The function accepts now the representation of the default state as empty sequence (as returned by The structure of the result is now the same on all platform and does not depend on the value of wantobjects.

  • bpo-42345: Fix various issues with typing.Literal parameter handling (flatten, deduplicate, use type to cache key). Patch provided by Yurii Karabas.

  • bpo-37205: time.perf_counter() on Windows and time.monotonic() on macOS are now system-wide. Previously, they used an offset computed at startup to reduce the precision loss caused by the float type. Use time.perf_counter_ns() and time.monotonic_ns() added in Python 3.7 to avoid this precision loss.

  • bpo-42318: Fixed support of non-BMP characters in tkinter on macOS.

  • bpo-42350: Fix the threading.Thread class at fork: do nothing if the thread is already stopped (ex: fork called at Python exit). Previously, an error was logged in the child process.

  • bpo-42333: Port _ssl extension module to heap types.

  • bpo-42014: The onerror callback from shutil.rmtree now receives correct function when fails.

  • bpo-42237: Fix os.sendfile() on illumos.

  • bpo-42308: Add threading.__excepthook__ to allow retrieving the original value of threading.excepthook() in case it is set to a broken or a different value. Patch by Mario Corchero.

  • bpo-42131: Implement PEP 451/spec methods on zipimport.zipimporter: find_spec(), create_module(), and exec_module().

    This also allows for the documented deprecation of find_loader(), find_module(), and load_module().

  • bpo-41877: Mock objects which are not unsafe will now raise an AttributeError if an attribute with the prefix asert, aseert, or assrt is accessed, in addition to this already happening for the prefixes assert or assret.

  • bpo-42264: sqlite3.OptimizedUnicode has been undocumented and obsolete since Python 3.3, when it was made an alias to str. It is now deprecated, scheduled for removal in Python 3.12.

  • bpo-42251: Added threading.gettrace() and threading.getprofile() to retrieve the functions set by threading.settrace() and threading.setprofile() respectively. Patch by Mario Corchero.

  • bpo-42249: Fixed writing binary Plist files larger than 4 GiB.

  • bpo-42236: On Unix, the os.device_encoding() function now returns 'UTF-8' rather than the device encoding if the Python UTF-8 Mode is enabled.

  • bpo-41754: webbrowser: Ignore NotADirectoryError when calling xdg-settings.

  • bpo-42183: Fix a stack overflow error for asyncio Task or Future repr().

    The overflow occurs under some circumstances when a Task or Future recursively returns itself.

  • bpo-42140: Improve asyncio.wait function to create the futures set just one time.

  • bpo-42133: Update various modules in the stdlib to fall back on __spec__.loader when __loader__ isn't defined on a module.

  • bpo-26131: The load_module() methods found in importlib now trigger a DeprecationWarning.

  • bpo-39825: Windows: Change sysconfig.get_config_var('EXT_SUFFIX') to the expected full platform_tag.extension format. Previously it was hard-coded to .pyd, now it is compatible with distutils.sysconfig and will result in something like .cp38-win_amd64.pyd. This brings windows into conformance with the other platforms.

  • bpo-26389: The traceback.format_exception(), traceback.format_exception_only(), and traceback.print_exception() functions can now take an exception object as a positional-only argument.

  • bpo-41889: Enum: fix regression involving inheriting a multiply-inherited enum

  • bpo-41861: Convert sqlite3 to use heap types (PEP 384). Patch by Erlend E. Aasland.

  • bpo-40624: Added support for the XPath != operator in xml.etree

  • bpo-28850: Fix pprint.PrettyPrinter.format() overrides being ignored for contents of small containers. The pprint._safe_repr() function was removed.

  • bpo-41625: Expose the splice() as os.splice() in the os module. Patch by Pablo Galindo

  • bpo-34215: Clarify the error message for asyncio.IncompleteReadError when expected is None.

  • bpo-41543: Add async context manager support for contextlib.nullcontext.

  • bpo-21041: pathlib.PurePath.parents now supports negative indexing. Patch contributed by Yaroslav Pankovych.

  • bpo-41332: Added missing connect_accepted_socket() method to asyncio.AbstractEventLoop.

  • bpo-12800: Extracting a symlink from a tarball should succeed and overwrite the symlink if it already exists. The fix is to remove the existing file or symlink before extraction. Based on patch by Chris AtLee, Jeffrey Kintscher, and Senthil Kumaran.

  • bpo-40968: urllib.request and http.client now send http/1.1 ALPN extension during TLS handshake when no custom context is supplied.

  • bpo-41001: Add func:os.eventfd to provide a low level interface for Linux's event notification file descriptor.

  • bpo-40816: Add AsyncContextDecorator to contextlib to support async context manager as a decorator.

  • bpo-40550: Fix time-of-check/time-of-action issue in subprocess.Popen.send_signal.

  • bpo-39411: Add an is_async identifier to pyclbr's Function objects. Patch by Batuhan Taskaya

  • bpo-35498: Add slice support to pathlib.PurePath.parents.


  • bpo-42238: Tentative to deprecate make suspicious by first removing it from the CI and documentation builds, but keeping it around for manual uses.

  • bpo-42153: Fix the URL for the IMAP protocol documents.

  • bpo-41028: Language and version switchers, previously maintained in every cpython branches, are now handled by docsbuild-script.


  • bpo-41473: Re-enable test_gdb on gdb 9.2 and newer: bug is fixed in gdb 10.1.

  • bpo-42553: Fix test_asyncio.test_call_later() race condition: don't measure asyncio performance in the call_later() unit test. The test failed randomly on the CI.

  • bpo-31904: Fix test_netrc on VxWorks: create temporary directories using temp_cwd().

  • bpo-31904: skip test_getaddrinfo_ipv6_scopeid_symbolic and test_getnameinfo_ipv6_scopeid_symbolic on VxWorks

  • bpo-31904: skip test_test of test_mailcap on VxWorks

  • bpo-31904: add shell requirement for test_pipes

  • bpo-31904: skip some tests related to fifo on VxWorks

  • bpo-31904: Fix failures for VxWorks.

  • bpo-40754: Include _testinternalcapi module in Windows installer for test suite

  • bpo-41561: test_ssl: skip test_min_max_version_mismatch when TLS 1.0 is not available

  • bpo-31904: Fix os module failures for VxWorks RTOS.

  • bpo-31904: Fix fifo test cases for VxWorks RTOS.


  • bpo-31904: remove libnet dependency from detect_socket() for VxWorks

  • bpo-42398: Fix a race condition in "make regen-all" when make -jN option is used to run jobs in parallel. The script now only use atomic write to write files. Moveover, generated files are now left unchanged if the content does not change, to not change the file modification time.

  • bpo-41617: Fix building pycore_bitutils.h internal header on old clang version without __builtin_bswap16() (ex: Xcode 4.6.3 on Mac OS X 10.7). Patch by Joshua Root and Victor Stinner.

  • bpo-38823: It is no longer possible to build the _ctypes extension module without wchar_t type: remove CTYPES_UNICODE macro. Anyway, the wchar_t type is required to build Python. Patch by Victor Stinner.

  • bpo-42087: Support was removed for AIX 5.3 and below. See bpo-40680.

  • bpo-40998: Addressed three compiler warnings found by undefined behavior sanitizer (ubsan).


  • bpo-42120: Remove macro definition of copysign (to _copysign) in headers.

  • bpo-38506: The Windows launcher now properly handles Python 3.10 when listing installed Python versions.


  • bpo-42504: Fix build on macOS Big Sur when MACOSX_DEPLOYMENT_TARGET=11

  • bpo-41116: Ensure distutils.unixxcompiler.find_library_file can find system provided libraries on macOS 11.

  • bpo-41100: Add support for macOS 11 and Apple Silicon systems.

    It is now possible to build "Universal 2" binaries using "--enable-universalsdk --with-universal-archs=universal2".

    Binaries build on later macOS versions can be deployed back to older versions (tested up to macOS 10.9), when using the correct deployment target. This is tested using Xcode 11 and later.

  • bpo-42232: Added Darwin specific madvise options to mmap module.

  • bpo-38443: The --enable-universalsdk and --with-universal-archs options for the configure script now check that the specified architectures can be used.


  • bpo-42508: Keep IDLE running on macOS. Remove obsolete workaround that prevented running files with shortcuts when using new universal2 installers built on macOS 11.

  • bpo-42426: Fix reporting offset of the RE error in searchengine.

  • bpo-42415: Get docstrings for IDLE calltips more often by using inspect.getdoc.


  • bpo-42212: The script now also checks the Python dynamic library and extension modules, not only the Python static library. Make also the script more verbose: explain what it does.

  • bpo-36310: Allow Tools/i18n/ to detect calls to gettext in f-strings.


Python 3.10.0 alpha 2

Release date: 2020-11-03


  • bpo-42103: Prevented potential DoS attack via CPU and RAM exhaustion when processing malformed Apple Property List files in binary format.

  • bpo-42051: The plistlib module no longer accepts entity declarations in XML plist files to avoid XML vulnerabilities. This should not affect users as entity declarations are not used in regular plist files.

Core and Builtins

  • bpo-42236: If the nl_langinfo(CODESET) function returns an empty string, Python now uses UTF-8 as the filesystem encoding. Patch by Victor Stinner.

  • bpo-42218: Fixed a bug in the PEG parser that was causing crashes in debug mode. Now errors are checked in left-recursive rules to avoid cases where such errors do not get handled in time and appear as long-distance crashes in other places.

  • bpo-42214: Fixed a possible crash in the PEG parser when checking for the '!=' token in the barry_as_flufl rule. Patch by Pablo Galindo.

  • bpo-42206: Propagate and raise the errors caused by PyAST_Validate() in the parser.

  • bpo-41796: The ast module internal state is now per interpreter. Patch by Victor Stinner.

  • bpo-42143: Fix handling of errors during creation of PyFunctionObject, which resulted in operations on uninitialized memory. Patch by Yonatan Goldschmidt.

  • bpo-41659: Fix a bug in the parser, where a curly brace following a primary didn't fail immediately. This led to invalid expressions like a {b} to throw a SyntaxError with a wrong offset, or invalid expressions ending with a curly brace like a { to not fail immediately in the REPL.

  • bpo-42150: Fix possible buffer overflow in the new parser when checking for continuation lines. Patch by Pablo Galindo.

  • bpo-42123: Run the parser two times. On the first run, disable all the rules that only generate better error messages to gain performance. If there's a parse failure, run the parser a second time with those enabled.

  • bpo-42093: The LOAD_ATTR instruction now uses new "per opcode cache" mechanism and it is about 36% faster now. Patch by Pablo Galindo and Yury Selivanov.

  • bpo-42030: Support for the legacy AIX-specific shared library loading support has been removed. All versions of AIX since 4.3 have supported and defaulted to using the common Unix mechanism instead.

  • bpo-41984: The garbage collector now tracks all user-defined classes. Patch by Brandt Bucher.

  • bpo-41993: Fixed potential issues with removing not completely initialized module from sys.modules when import fails.

  • bpo-41979: Star-unpacking is now allowed for with item's targets in the PEG parser.

  • bpo-41974: Removed special methods __int__, __float__, __floordiv__, __mod__, __divmod__, __rfloordiv__, __rmod__ and __rdivmod__ of the complex class. They always raised a TypeError.

  • bpo-41902: Micro optimization when compute sq_item and mp_subscript of range. Patch by Dong-hee Na.

  • bpo-41894: When loading a native module and a load failure occurs, prevent a possible UnicodeDecodeError when not running in a UTF-8 locale by decoding the load error message using the current locale's encoding.

  • bpo-41902: Micro optimization for range.index if step is 1. Patch by Dong-hee Na.

  • bpo-41435: Add sys._current_exceptions() function to retrieve a dictionary mapping each thread's identifier to the topmost exception currently active in that thread at the time the function is called.

  • bpo-38605: Enable from __future__ import annotations (PEP 563) by default. The values found in __annotations__ dicts are now strings, e.g. {"x": "int"} instead of {"x": int}.


  • bpo-35455: On Solaris, thread_time() is now implemented with gethrvtime() because clock_gettime(CLOCK_THREAD_CPUTIME_ID) is not always available. Patch by Jakub Kulik.

  • bpo-42233: The repr() of typing types containing Generic Alias Types previously did not show the parameterized types in the GenericAlias. They have now been changed to do so.

  • bpo-29566: binhex.binhex() consistently writes macOS 9 line endings.

  • bpo-26789: The logging.FileHandler class now keeps a reference to the builtin open() function to be able to open or reopen the file during Python finalization. Fix errors like: NameError: name 'open' is not defined. Patch by Victor Stinner.

  • bpo-42157: Removed the unicodedata.ucnhash_CAPI attribute which was an internal PyCapsule object. The related private _PyUnicode_Name_CAPI structure was moved to the internal C API. Patch by Victor Stinner.

  • bpo-42157: Convert the unicodedata extension module to the multiphase initialization API (PEP 489) and convert the unicodedata.UCD static type to a heap type. Patch by Mohamed Koubaa and Victor Stinner.

  • bpo-42146: Fix memory leak in subprocess.Popen() in case an uid (gid) specified in user (group, extra_groups) overflows uid_t (gid_t).

  • bpo-42103: InvalidFileException and RecursionError are now the only errors caused by loading malformed binary Plist file (previously ValueError and TypeError could be raised in some specific cases).

  • bpo-41490: In importlib.resources, .path method is more aggressive about releasing handles to zipfile objects early, enabling use-cases like certifi to leave the context open but delete the underlying zip file.

  • bpo-41052: Pickling heap types implemented in C with protocols 0 and 1 raises now an error instead of producing incorrect data.

  • bpo-42089: In importlib.metadata.PackageNotFoundError, make reference to the package metadata being missing to improve the user experience.

  • bpo-41491: plistlib: fix parsing XML plists with hexadecimal integer values

  • bpo-42065: Fix an incorrectly formatted error from _codecs.charmap_decode() when called with a mapped value outside the range of valid Unicode code points. PR by Max Bernstein.

  • bpo-41966: Fix pickling pure Python datetime.time subclasses. Patch by Dean Inwood.

  • bpo-19270: sched.scheduler.cancel() will now cancel the correct event, if two events with same priority are scheduled for the same time. Patch by Bar Harel.

  • bpo-28660: textwrap.wrap() now attempts to break long words after hyphens when break_long_words=True and break_on_hyphens=True.

  • bpo-35823: Use vfork() instead of fork() for subprocess.Popen() on Linux to improve performance in cases where it is deemed safe.

  • bpo-42043: Add support for zipfile.Path inheritance. zipfile.Path.is_file() now returns False for non-existent names. zipfile.Path objects now expose a .filename attribute and rely on that to resolve .name and .parent when the Path object is at the root of the zipfile.

  • bpo-42021: Fix possible ref leaks in sqlite3 module init.

  • bpo-39101: Fixed tests using IsolatedAsyncioTestCase from hanging on BaseExceptions.

  • bpo-41976: Fixed a bug that was causing ctypes.util.find_library() to return None when triying to locate a library in an environment when gcc>=9 is available and ldconfig is not. Patch by Pablo Galindo

  • bpo-41943: Fix bug where TestCase.assertLogs doesn't correctly filter messages by level.

  • bpo-41923: Implement PEP 613, introducing typing.TypeAlias annotation.

  • bpo-41905: A new function in abc: update_abstractmethods to re-calculate an abstract class's abstract status. In addition, dataclass has been changed to call this function.

  • bpo-23706: Added newline parameter to pathlib.Path.write_text().

  • bpo-41876: Tkinter font class repr uses font name

  • bpo-41831: str() for the type attribute of the tkinter.Event object always returns now the numeric code returned by Tk instead of the name of the event type.

  • bpo-39337: encodings.normalize_encoding() now ignores non-ASCII characters.

  • bpo-41747: Ensure all methods that generated from dataclasses.dataclass() objects now have the proper __qualname__ attribute referring to the class they belong to. Patch by Batuhan Taskaya.

  • bpo-30681: Handle exceptions caused by unparsable date headers when using email "default" policy. Patch by Tim Bell, Georges Toth

  • bpo-41586: Add F_SETPIPE_SZ and F_GETPIPE_SZ to fcntl module. Allow setting pipesize on subprocess.Popen.

  • bpo-41229: Add contextlib.aclosing for deterministic cleanup of async generators which is analogous to contextlib.closing for non-async generators. Patch by Joongi Kim and John Belmonte.

  • bpo-16396: Allow ctypes.wintypes to be imported on non-Windows systems.

  • bpo-4356: Add a key function to the bisect module.

  • bpo-40592: shutil.which() now ignores empty entries in PATHEXT instead of treating them as a match.

  • bpo-40492: Fix --outfile for cProfile / profile not writing the output file in the original directory when the program being profiled changes the working directory. PR by Anthony Sottile.

  • bpo-34204: The shelve module now uses pickle.DEFAULT_PROTOCOL by default instead of pickle protocol 3.

  • bpo-27321: Fixed KeyError exception when flattening an email to a string attempts to replace a non-existent Content-Transfer-Encoding header.

  • bpo-38976: The http.cookiejar module now supports the parsing of cookies in CURL-style cookiejar files through MozillaCookieJar on all platforms. Previously, such cookie entries would be silently ignored when loading a cookiejar with such entries.

    Additionally, the HTTP Only attribute is persisted in the object, and will be correctly written to file if the MozillaCookieJar object is subsequently dumped.



  • bpo-41739: Fix test_logging.test_race_between_set_target_and_flush(): the test now waits until all threads complete to avoid leaking running threads.

  • bpo-41970: Avoid a test failure in test_lib2to3 if the module has already imported at the time the test executes. Patch by Pablo Galindo.

  • bpo-41944: Tests for CJK codecs no longer call eval() on content received via HTTP.

  • bpo-41306: Fixed a failure in test_tk.test_widgets.ScaleTest happening when executing the test with Tk 8.6.10.


  • bpo-38980: Add -fno-semantic-interposition to both the compile and link line when building with --enable-optimizations. Patch by Victor Stinner and Pablo Galindo.


  • bpo-38439: Updates the icons for IDLE in the Windows Store package.

  • bpo-38252: Use 8-byte step to detect ASCII sequence in 64-bit Windows build.

  • bpo-39107: Update Tcl and Tk to 8.6.10 in Windows installer.

  • bpo-41557: Update Windows installer to use SQLite 3.33.0.

  • bpo-38324: Avoid Unicode errors when accessing certain locale data on Windows.


  • bpo-41471: Ignore invalid prefix lengths in system proxy excludes.


  • bpo-33987: Mostly finish using ttk widgets, mainly for editor, settings, and searches. Some patches by Mark Roseman.

  • bpo-40511: Typing opening and closing parentheses inside the parentheses of a function call will no longer cause unnecessary "flashing" off and on of an existing open call-tip, e.g. when typed in a string literal.

  • bpo-38439: Add a 256×256 pixel IDLE icon to the Windows .ico file. Created by Andrew Clover. Remove the low-color gif variations from the .ico file.


  • bpo-42157: The private _PyUnicode_Name_CAPI structure of the PyCapsule API unicodedata.ucnhash_CAPI has been moved to the internal C API. Patch by Victor Stinner.

  • bpo-42015: Fix potential crash in deallocating method objects when dynamically allocated PyMethodDef's lifetime is managed through the self argument of a PyCFunction.

  • bpo-40423: The subprocess module and os.closerange will now use the close_range(low, high, flags) syscall when it is available for more efficient closing of ranges of descriptors.

  • bpo-41845: PyObject_GenericGetDict() is available again in the limited API when targeting 3.10 or later.

  • bpo-40422: Add _Py_closerange function to provide performant closing of a range of file descriptors.

  • bpo-41986: Py_FileSystemDefaultEncodeErrors and Py_UTF8Mode are available again in limited API.

  • bpo-41756: Add PyIter_Send function to allow sending value into generator/coroutine/iterator without raising StopIteration exception to signal return.

  • bpo-41784: Added PyUnicode_AsUTF8AndSize to the limited C API.

Python 3.10.0 alpha 1

Release date: 2020-10-05


  • bpo-41304: Fixes python3x._pth being ignored on Windows, caused by the fix for bpo-29778 (CVE-2020-15801).

  • bpo-41162: Audit hooks are now cleared later during finalization to avoid missing events.

  • bpo-29778: Ensure python3.dll is loaded from correct locations when Python is embedded (CVE-2020-15523).

  • bpo-41004: The __hash__() methods of ipaddress.IPv4Interface and ipaddress.IPv6Interface incorrectly generated constant hash values of 32 and 128 respectively. This resulted in always causing hash collisions. The fix uses hash() to generate hash values for the tuple of (address, mask length, network address).

  • bpo-39603: Prevent http header injection by rejecting control characters in http.client.putrequest(...).

Core and Builtins

  • bpo-41909: Fixed stack overflow in issubclass() and isinstance() when getting the __bases__ attribute leads to infinite recursion.

  • bpo-41922: Speed up calls to reversed() by using the PEP 590 vectorcall calling convention. Patch by Dong-hee Na.

  • bpo-41873: Calls to float() are now faster due to the vectorcall calling convention. Patch by Dennis Sweeney.

  • bpo-41870: Speed up calls to bool() by using the PEP 590 vectorcall calling convention. Patch by Dong-hee Na.

  • bpo-1635741: Port the _bisect module to the multi-phase initialization API (PEP 489).

  • bpo-39934: Correctly count control blocks in 'except' in compiler. Ensures that a syntax error, rather a fatal error, occurs for deeply nested, named exception handlers.

  • bpo-41780: Fix __dir__() of types.GenericAlias. Patch by Batuhan Taskaya.

  • bpo-1635741: Port the _lsprof extension module to multi-phase initialization (PEP 489).

  • bpo-1635741: Port the cmath extension module to multi-phase initialization (PEP 489).

  • bpo-1635741: Port the _scproxy extension module to multi-phase initialization (PEP 489).

  • bpo-1635741: Port the termios extension module to multi-phase initialization (PEP 489).

  • bpo-1635741: Convert the _sha256 extension module types to heap types.

  • bpo-41690: Fix a possible stack overflow in the parser when parsing functions and classes with a huge amount of arguments. Patch by Pablo Galindo.

  • bpo-1635741: Port the _overlapped extension module to multi-phase initialization (PEP 489).

  • bpo-1635741: Port the _curses_panel extension module to multi-phase initialization (PEP 489).

  • bpo-1635741: Port the _opcode extension module to multi-phase initialization (PEP 489).

  • bpo-41681: Fixes the wrong error description in the error raised by using 2 , in format string in f-string and str.format().

  • bpo-41675: The implementation of signal.siginterrupt() now uses sigaction() (if it is available in the system) instead of the deprecated siginterrupt(). Patch by Pablo Galindo.

  • bpo-41670: Prevent line trace being skipped on platforms not compiled with USE_COMPUTED_GOTOS. Fixes issue where some lines nested within a try-except block were not being traced on Windows.

  • bpo-41654: Fix a crash that occurred when destroying subclasses of MemoryError. Patch by Pablo Galindo.

  • bpo-1635741: Port the zlib extension module to multi-phase initialization (PEP 489).

  • bpo-41631: The _ast module uses again a global state. Using a module state per module instance is causing subtle practical problems. For example, the Mercurial project replaces the __import__() function to implement lazy import, whereas Python expected that import _ast always return a fully initialized _ast module.

  • bpo-40077: Convert _operator to use PyType_FromSpec().

  • bpo-1653741: Port _sha3 to multi-phase init. Convert static types to heap types.

  • bpo-1635741: Port the _blake2 extension module to the multi-phase initialization API (PEP 489).

  • bpo-41533: Free the stack allocated in va_build_stack if do_mkstack fails and the stack is not a small_stack.

  • bpo-41531: Fix a bug that was dropping keys when compiling dict literals with more than 0xFFFF elements. Patch by Pablo Galindo.

  • bpo-41525: The output of python --help contains now only ASCII characters.

  • bpo-1635741: Port the _sha1, _sha512, and _md5 extension modules to multi-phase initialization API (PEP 489).

  • bpo-41431: Optimize dict_merge() for copying dict (e.g. dict(d) and {}.update(d)).

  • bpo-41428: Implement PEP 604. This supports (int | str) etc. in place of Union[str, int].

  • bpo-41340: Removed fallback implementation for strdup.

  • bpo-38156: Handle interrupts that come after EOF correctly in PyOS_StdioReadline.

  • bpo-41342: round() with integer argument is now faster (9--60%).

  • bpo-41334: Constructors str(), bytes() and bytearray() are now faster (around 30--40% for small objects).

  • bpo-41295: Resolve a regression in CPython 3.8.4 where defining "__setattr__" in a multi-inheritance setup and calling up the hierarchy chain could fail if builtins/extension types were involved in the base types.

  • bpo-41323: Bytecode optimizations are performed directly on the control flow graph. This will result in slightly more compact code objects in some circumstances.

  • bpo-41247: Always cache the running loop holder when running asyncio.set_running_loop.

  • bpo-41252: Fix incorrect refcounting in _ssl.c's _servername_callback().

  • bpo-1635741: Port multiprocessing to multi-phase initialization

  • bpo-1635741: Port winapi to multiphase initialization

  • bpo-41215: Use non-NULL default values in the PEG parser keyword list to overcome a bug that was preventing Python from being properly compiled when using the XLC compiler. Patch by Pablo Galindo.

  • bpo-41218: Python 3.8.3 had a regression where compiling with ast.PyCF_ALLOW_TOP_LEVEL_AWAIT would aggressively mark list comprehension with CO_COROUTINE. Now only list comprehension making use of async/await will tagged as so.

  • bpo-1635741: Port faulthandler to multiphase initialization.

  • bpo-1635741: Port sha256 to multiphase initialization

  • bpo-41175: Guard against a NULL pointer dereference within bytearrayobject triggered by the bytearray() + bytearray() operation.

  • bpo-41100: add arm64 to the allowable Mac OS arches in mpdecimal.h

  • bpo-41094: Fix decoding errors with audit when open files with non-ASCII names on non-UTF-8 locale.

  • bpo-39960: The "hackcheck" that prevents sneaking around a type's __setattr__() by calling the superclass method was rewritten to allow C implemented heap types.

  • bpo-41084: Prefix the error message with 'f-string: ', when parsing an f-string expression which throws a SyntaxError.

  • bpo-40521: Empty frozensets are no longer singletons.

  • bpo-41076: Pre-feed the parser with the location of the f-string expression, not the f-string itself, which allows us to skip the shifting of the AST node locations after the parsing is completed.

  • bpo-41056: Fixes a reference to deallocated stack space during startup when constructing sys.path involving a relative symlink when code was supplied via -c. (discovered via Coverity)

  • bpo-41061: Fix incorrect expressions and asserts in hashtable code and tests.

  • bpo-41052: Opt out serialization/deserialization for _random.Random

  • bpo-40939: Rename PyPegen* functions to PyParser*, so that we can remove the old set of PyParser* functions that were using the old parser, but keep everything backwards-compatible.

  • bpo-35975: Stefan Behnel reported that cf_feature_version is used even when PyCF_ONLY_AST is not set. This is against the intention and against the documented behavior, so it's been fixed.

  • bpo-40939: Remove the remaining files from the old parser and the symbol module.

  • bpo-40077: Convert _bz2 to use PyType_FromSpec().

  • bpo-41006: The encodings.latin_1 module is no longer imported at startup. Now it is only imported when it is the filesystem encoding or the stdio encoding.

  • bpo-40636: zip() now supports PEP 618's strict parameter, which raises a ValueError if the arguments are exhausted at different lengths. Patch by Brandt Bucher.

  • bpo-1635741: Port _gdbm to multiphase initialization.

  • bpo-40985: Fix a bug that caused the SyntaxError text to be empty when a file ends with a line ending in a line continuation character (i.e. backslash). The error text should contain the text of the last line.

  • bpo-40958: Fix a possible buffer overflow in the PEG parser when gathering information for emitting syntax errors. Patch by Pablo Galindo.

  • bpo-1635741: Port _dbm to multiphase initialization.

  • bpo-40957: Fix refleak in _Py_fopen_obj() when PySys_Audit() fails

  • bpo-40950: Add a state to the nis module (PEP 3121) and apply the multiphase initialization. Patch by Dong-hee Na.

  • bpo-40947: The Python Path Configuration now takes PyConfig.platlibdir in account.

  • bpo-40939: Remove the old parser, the parser module and all associated support code, command-line options and environment variables. Patch by Pablo Galindo.

  • bpo-40847: Fix a bug where a line with only a line continuation character is not considered a blank line at tokenizer level. In such cases, more than a single NEWLINE token was emitted. The old parser was working around the issue, but the new parser threw a SyntaxError for valid input due to this. For example, an empty line following a line continuation character was interpreted as a SyntaxError.

  • bpo-40890: Each dictionary view now has a mapping attribute that provides a types.MappingProxyType wrapping the original dictionary. Patch contributed by Dennis Sweeney.

  • bpo-40889: Improved the performance of symmetric difference operations on dictionary item views. Patch by Dennis Sweeney.

  • bpo-40904: Fix possible segfault in the new PEG parser when parsing f-string containing yield statements with no value (f"{yield}"). Patch by Pablo Galindo

  • bpo-40903: Fixed a possible segfault in the new PEG parser when producing error messages for invalid assignments of the form p=p=. Patch by Pablo Galindo

  • bpo-40880: Fix invalid memory read in the new parser when checking newlines in string literals. Patch by Pablo Galindo.

  • bpo-40883: Fix memory leak in when parsing f-strings in the new parser. Patch by Pablo Galindo

  • bpo-40870: Raise ValueError when validating custom AST's where the constants True, False and None are used within a ast.Name node.

  • bpo-40854: Allow overriding sys.platlibdir via a new PYTHONPLATLIBDIR environment variable.

  • bpo-40826: Fix GIL usage in PyOS_Readline(): lock the GIL to set an exception and pass the Python thread state when checking if there is a pending signal.

  • bpo-1635741: Port fcntl to multiphase initialization.

  • bpo-19468: Delete unnecessary instance check in importlib.reload(). Patch by Furkan Önder.

  • bpo-40824: Unexpected errors in calling the __iter__ method are no longer masked by TypeError in the in operator and functions contains(), indexOf() and countOf() of the operator module.

  • bpo-40792: Attributes start, stop and step of the range object now always has exact type int. Previously, they could have been an instance of a subclass of int.

  • bpo-40780: Fix a corner case where g-style string formatting of a float failed to remove trailing zeros.

  • bpo-38964: When there's a SyntaxError in the expression part of an fstring, the filename attribute of the SyntaxError gets correctly set to the name of the file the fstring resides in.

  • bpo-40750: Support the "-d" debug flag in the new PEG parser. Patch by Pablo Galindo

  • bpo-40217: Instances of types created with PyType_FromSpecWithBases() will no longer automatically visit their class object when traversing references in the garbage collector. The user is expected to manually visit the object's class. Patch by Pablo Galindo.

  • bpo-39573: Py_TYPE() is changed to the inline static function. Patch by Dong-hee Na.

  • bpo-40696: Fix a hang that can arise after generator.throw() due to a cycle in the exception context chain.

  • bpo-40521: Each interpreter now its has own free lists, singletons and caches:

    • Free lists: float, tuple, list, dict, frame, context, asynchronous generator, MemoryError.

    • Singletons: empty tuple, empty bytes string, empty Unicode string, single byte character, single Unicode (latin1) character.

    • Slice cache.

    They are no longer shared by all interpreters.

  • bpo-40679: Certain TypeError messages about missing or extra arguments now include the function's qualified name. Patch by Dennis Sweeney.

  • bpo-29590: Make the stack trace correct after calling generator.throw() on a generator that has yielded from a yield from.

  • bpo-4022: Improve performance of generators by not raising internal StopIteration.

  • bpo-1635741: Port mmap to multiphase initialization.

  • bpo-1635741: Port _lzma to multiphase initialization.

  • bpo-37999: Builtin and extension functions that take integer arguments no longer accept Decimals, Fractions and other objects that can be converted to integers only with a loss (e.g. that have the __int__() method but do not have the __index__() method).

  • bpo-29882: Add int.bit_count(), counting the number of ones in the binary representation of an integer. Patch by Niklas Fiekas.

  • bpo-36982: Use ncurses extended color functions when available to support terminals with 256 colors, and add the new function curses.has_extended_color_support() to indicate whether extended color support is provided by the underlying ncurses library.

  • bpo-19569: Add the private macros _Py_COMP_DIAG_PUSH, _Py_COMP_DIAG_IGNORE_DEPR_DECLS, and _Py_COMP_DIAG_POP.

  • bpo-26680: The int type now supports the x.is_integer() method for compatibility with float.


  • bpo-41900: C14N 2.0 serialisation in xml.etree.ElementTree failed for unprefixed attributes when a default namespace was defined.

  • bpo-41887: Strip leading spaces and tabs on ast.literal_eval(). Also document stripping of spaces and tabs for eval().

  • bpo-41773: Note in documentation that random.choices() doesn't support non-finite weights, raise ValueError when given non-finite weights.

  • bpo-41840: Fix a bug in the symtable module that was causing module-scope global variables to not be reported as both local and global. Patch by Pablo Galindo.

  • bpo-41842: Add codecs.unregister() function to unregister a codec search function.

  • bpo-40564: In zipfile.Path, mutate the passed ZipFile object type instead of making a copy. Prevents issues when both the local copy and the caller’s copy attempt to close the same file handle.

  • bpo-40670: More reliable validation of statements in timeit.Timer. It now accepts "empty" statements (only whitespaces and comments) and rejects misindentent statements.

  • bpo-41833: The threading.Thread constructor now uses the target name if the target argument is specified but the name argument is omitted.

  • bpo-41817: fix tkinter.EventType Enum so all members are strings, and none are tuples

  • bpo-41810: types.EllipsisType, types.NotImplementedType and types.NoneType have been reintroduced, providing a new set of types readily interpretable by static type checkers.

  • bpo-41815: Fix SQLite3 segfault when backing up closed database. Patch contributed by Peter David McCormick.

  • bpo-41816: StrEnum added: it ensures that all members are already strings or string candidates

  • bpo-41517: fix bug allowing Enums to be extended via multiple inheritance

  • bpo-39587: use the correct mix-in data type when constructing Enums

  • bpo-41792: Add is_typeddict function to to check if a type is a TypedDict class

    Previously there was no way to check that without using private API. See the relevant issue in python/typing

  • bpo-41789: Honor object overrides in Enum class creation (specifically, __str__, __repr__, __format__, and __reduce_ex__).

  • bpo-32218: enum.Flag and enum.IntFlag members are now iterable

  • bpo-39651: Fix a race condition in the call_soon_threadsafe() method of asyncio.ProactorEventLoop: do nothing if the self-pipe socket has been closed.

  • bpo-1635741: Port the mashal extension module to the multi-phase initialization API (PEP 489).

  • bpo-1635741: Port the _string extension module to the multi-phase initialization API (PEP 489).

  • bpo-41732: Added an iterator to memoryview.

  • bpo-41720: Fixed turtle.Vec2D.__rmul__() for arguments which are not int or float.

  • bpo-41696: Fix handling of debug mode in This allows setting PYTHONASYNCIODEBUG or -X dev to enable asyncio debug mode when using

  • bpo-41687: Fix implementation of sendfile to be compatible with Solaris.

  • bpo-41662: No longer override exceptions raised in __len__() of a sequence of parameters in sqlite3 with ProgrammingError.

  • bpo-39010: Restarting a ProactorEventLoop on Windows no longer logs spurious ConnectionResetErrors.

  • bpo-41638: ProgrammingError message for absent parameter in sqlite3 contains now the name of the parameter instead of its index when parameters are supplied as a dict.

  • bpo-41662: Fixed crash when mutate list of parameters during iteration in sqlite3.

  • bpo-41513: Improved the accuracy of math.hypot(). Internally, each step is computed with extra precision so that the result is now almost always correctly rounded.

  • bpo-41609: The pdb whatis command correctly reports instance methods as 'Method' rather than 'Function'.

  • bpo-39994: Fixed pprint's handling of dict subclasses that override __repr__.

  • bpo-32751: When cancelling the task due to a timeout, asyncio.wait_for() will now wait until the cancellation is complete also in the case when timeout is <= 0, like it does with positive timeouts.

  • bpo-37658: asyncio.wait_for() now properly handles races between cancellation of itself and the completion of the wrapped awaitable.

  • bpo-40782: Change the method asyncio.AbstractEventLoop.run_in_executor to not be a coroutine.

  • bpo-41520: Fix codeop regression that prevented turning compile warnings into errors.

  • bpo-41528: turtle uses math module functions to convert degrees to radians and vice versa and to calculate vector norm

  • bpo-41513: Minor algorithmic improvement to math.hypot() and math.dist() giving small gains in speed and accuracy.

  • bpo-41503: Fixed a race between setTarget and flush in logging.handlers.MemoryHandler.

  • bpo-41497: Fix potential UnicodeDecodeError in dis module.

  • bpo-41467: On Windows, fix asyncio recv_into() return value when the socket/pipe is closed (BrokenPipeError): return 0 rather than an empty byte string (b'').

  • bpo-41425: Make tkinter doc example runnable.

  • bpo-41421: Make an algebraic simplification to random.paretovariate(). It now is slightly less subject to round-off error and is slightly faster. Inputs that used to cause ZeroDivisionError now cause an OverflowError instead.

  • bpo-41440: Add os.cpu_count() support for VxWorks RTOS.

  • bpo-41316: Fix the tarfile module to write only basename of TAR file to GZIP compression header.

  • bpo-41384: Raise TclError instead of TypeError when an unknown option is passed to tkinter.OptionMenu.

  • bpo-41317: Use add_done_callback() in asyncio.loop.sock_accept() to unsubscribe reader early on cancellation.

  • bpo-41364: Reduce import overhead of uuid.

  • bpo-35328: Set the environment variable VIRTUAL_ENV_PROMPT at venv activation.

  • bpo-41341: Recursive evaluation of typing.ForwardRef in get_type_hints.

  • bpo-41344: Prevent creating shared_memory.SharedMemory objects with size=0.

  • bpo-41333: collections.OrderedDict.pop() is now 2 times faster.

  • bpo-41288: Unpickling invalid NEWOBJ_EX opcode with the C implementation raises now UnpicklingError instead of crashing.

  • bpo-39017: Avoid infinite loop when reading specially crafted TAR files using the tarfile module (CVE-2019-20907).

  • bpo-41273: Speed up any transport using _ProactorReadPipeTransport by calling recv_into instead of recv, thus not creating a new buffer for each recv call in the transport's read loop.

  • bpo-41235: Fix the error handling in ssl.SSLContext.load_dh_params().

  • bpo-41207: In distutils.spawn, restore expectation that DistutilsExecError is raised when the command is not found.

  • bpo-29727: Register array.array as a MutableSequence. Patch by Pablo Galindo.

  • bpo-39168: Remove the __new__ method of typing.Generic.

  • bpo-41194: Fix a crash in the _ast module: it can no longer be loaded more than once. It now uses a global state rather than a module state.

  • bpo-41195: Add read-only ssl.SSLContext.security_level attribute to retrieve the context's security level.

  • bpo-41193: The write_history() atexit function of the readline completer now ignores any OSError to ignore error if the filesystem is read-only, instead of only ignoring FileNotFoundError and PermissionError.

  • bpo-41182: selector: use DefaultSelector based upon implementation

  • bpo-41161: The decimal module now requires libmpdec-2.5.0. Users of --with-system-libmpdec should update their system library.

  • bpo-40874: The decimal module now requires libmpdec-2.5.0.

  • bpo-41138: Fixed the trace module CLI for Python source files with non-UTF-8 encoding.

  • bpo-31082: Use the term "iterable" in the docstring for functools.reduce().

  • bpo-40521: Remove freelist from collections.deque().

  • bpo-31938: Fix default-value signatures of several functions in the select module - by Anthony Sottile.

  • bpo-41068: Fixed reading files with non-ASCII names from ZIP archive directly after writing them.

  • bpo-41058: pdb.find_function() now correctly determines the source file encoding.

  • bpo-41056: Invalid file descriptor values are now prevented from being passed to os.fpathconf. (discovered by Coverity)

  • bpo-41056: Fix a NULL pointer dereference within the ssl module during a MemoryError in the keylog callback. (discovered by Coverity)

  • bpo-41056: Fixed an instance where a MemoryError within the zoneinfo module might not be reported or not reported at its source. (found by Coverity)

  • bpo-41048: mimetypes.read_mime_types() function reads the rule file using UTF-8 encoding, not the locale encoding. Patch by Srinivas Reddy Thatiparthy.

  • bpo-41043: Fixed the use of glob() in the stdlib: literal part of the path is now always correctly escaped.

  • bpo-41025: Fixed an issue preventing the C implementation of zoneinfo.ZoneInfo from being subclassed.

  • bpo-35018: Add the xml.sax.handler.LexicalHandler class that is present in other SAX XML implementations.

  • bpo-41002: Improve performance of with a given amount. Patch by Bruce Merry.

  • bpo-40448: ensurepip now disables the use of pip cache when installing the bundled versions of pip and setuptools. Patch by Krzysztof Konopko.

  • bpo-40967: Removed asyncio.Task.current_task() and asyncio.Task.all_tasks(). Patch contributed by Rémi Lapeyre.

  • bpo-40924: Ensure importlib.resources.path returns an extant path for the SourceFileLoader's resource reader. Avoids the regression identified in master while a long-term solution is devised.

  • bpo-40955: Fix a minor memory leak in subprocess module when extra_groups was specified.

  • bpo-40855: The standard deviation and variance functions in the statistics module were ignoring their mu and xbar arguments.

  • bpo-40939: Use the new PEG parser when generating the stdlib keyword module.

  • bpo-23427: Add sys.orig_argv attribute: the list of the original command line arguments passed to the Python executable.

  • bpo-33689: Ignore empty or whitespace-only lines in .pth files. This matches the documentated behavior. Before, empty lines caused the site-packages dir to appear multiple times in sys.path. By Ido Michael, contributors Malcolm Smith and Tal Einat.

  • bpo-40884: Added a defaults parameter to logging.Formatter, to allow specifying default values for custom fields. Patch by Asaf Alon and Bar Harel.

  • bpo-40876: Clarify error message in the csv module.

  • bpo-39791: Refresh importlib.metadata from importlib_metadata 1.6.1.

  • bpo-40807: Stop codeop._maybe_compile, used by code.InteractiveInterpreter (and IDLE). from emitting each warning three times.

  • bpo-32604: Fix reference leak in the select module when the module is imported in a subinterpreter.

  • bpo-39791: Built-in loaders (SourceFileLoader and ZipImporter) now supply TraversableResources implementations for ResourceReader, and the fallback function has been removed.

  • bpo-39314: rlcompleter.Completer and the standard Python shell now close the parenthesis for functions that take no arguments. Patch contributed by Rémi Lapeyre.

  • bpo-17005: The topological sort functionality that was introduced initially in the functools module has been moved to a new graphlib module to better accommodate the new tools and keep the original scope of the functools module. Patch by Pablo Galindo

  • bpo-40834: Fix truncate when sending str object with_xxsubinterpreters.channel_send.

  • bpo-40755: Add rich comparisons to collections.Counter().

  • bpo-26407: Unexpected errors in calling the __iter__ method are no longer masked by TypeError in csv.reader(), csv.writer.writerow() and csv.writer.writerows().

  • bpo-39384: Fixed email.contentmanager to allow set_content() to set a null string.

  • bpo-40744: The sqlite3 module uses SQLite API functions that require SQLite v3.7.3 or higher. This patch removes support for older SQLite versions, and explicitly requires SQLite 3.7.3 both at build, compile and runtime. Patch by Sergey Fedoseev and Erlend E. Aasland.

  • bpo-40777: Initialize PyDateTime_IsoCalendarDateType.tp_base at run-time to avoid errors on some compilers.

  • bpo-38488: Update ensurepip to install pip 20.1.1 and setuptools 47.1.0.

  • bpo-40792: The result of operator.index() now always has exact type int. Previously, the result could have been an instance of a subclass of int.

  • bpo-40767: webbrowser now properly finds the default browser in pure Wayland systems by checking the WAYLAND_DISPLAY environment variable. Patch contributed by Jérémy Attali.

  • bpo-40791: hashlib.compare_digest() uses OpenSSL's CRYPTO_memcmp() function when OpenSSL is available.

  • bpo-40795: ctypes module: If ctypes fails to convert the result of a callback or if a ctypes callback function raises an exception, sys.unraisablehook is now called with an exception set. Previously, the error was logged into stderr by PyErr_Print().

  • bpo-16995: Add base64.b32hexencode() and base64.b32hexdecode() to support the Base32 Encoding with Extended Hex Alphabet.

  • bpo-30008: Fix ssl code to be compatible with OpenSSL 1.1.x builds that use no-deprecated and --api=1.1.0.

  • bpo-30064: Fix asyncio loop.sock_* race condition issue

  • bpo-40759: Deprecate the symbol module.

  • bpo-40756: The second argument (extra) of LoggerAdapter.__init__ now defaults to None.

  • bpo-37129: Add a new os.RWF_APPEND flag for os.pwritev().

  • bpo-40737: Fix possible reference leak for sqlite3 initialization.

  • bpo-40726: Handle cases where the end_lineno is None on ast.increment_lineno().

  • bpo-40698: distutils upload creates SHA2-256 and Blake2b-256 digests. MD5 digests is skipped if platform blocks MD5.

  • bpo-40695: hashlib no longer falls back to builtin hash implementations when OpenSSL provides a hash digest and the algorithm is blocked by security policy.

  • bpo-9216: passed usedforsecurity to OpenSSL EVP constructor test_hashlib and test_smtplib handle strict security policy better.

  • bpo-40614: ast.parse() will not parse self documenting expressions in f-strings when passed feature_version is less than (3, 8).

  • bpo-40626: Add h5 file extension as MIME Type application/x-hdf5, as per HDF Group recommendation for HDF5 formatted data files. Patch contributed by Mark Schwab.

  • bpo-25920: On macOS, when building Python for macOS 10.4 and older, which wasn't the case for macOS installer, socket.getaddrinfo() no longer uses an internal lock to prevent race conditions when calling getaddrinfo() which is thread-safe since macOS 10.5. Python 3.9 requires macOS 10.6 or newer. The internal lock caused random hang on fork when another thread was calling socket.getaddrinfo(). The lock was also used on FreeBSD older than 5.3, OpenBSD older than 201311 and NetBSD older than 4.

  • bpo-40671: Prepare _hashlib for PEP 489 and use PyModule_AddType().

  • bpo-32309: Added a new coroutine asyncio.to_thread(). It is mainly used for running IO-bound functions in a separate thread to avoid blocking the event loop, and essentially works as a high-level version of run_in_executor() that can directly take keyword arguments.

  • bpo-36543: Restored the deprecated xml.etree.cElementTree module.

  • bpo-40611: MAP_POPULATE constant has now been added to the list of exported mmap module flags.

  • bpo-39881: PEP 554 for use in the test suite. (Patch By Joannah Nanjekye)

  • bpo-13097: ctypes now raises an ArgumentError when a callback is invoked with more than 1024 arguments.

  • bpo-39385: A new test assertion context-manager, unittest.assertNoLogs() will ensure a given block of code emits no log messages using the logging module. Contributed by Kit Yan Choi.

  • bpo-23082: Updated the error message and docs of PurePath.relative_to() to better reflect the function behaviour.

  • bpo-40318: Use SQLite3 trace v2 API, if it is available.

  • bpo-40105: ZipFile truncates files to avoid corruption when a shorter comment is provided in append ("a") mode. Patch by Jan Mazur.

  • bpo-40084: Fix Enum.__dir__: dir(Enum.member) now includes attributes as well as methods.

  • bpo-31122: ssl.wrap_socket() now raises ssl.SSLEOFError rather than OSError when peer closes connection during TLS negotiation

  • bpo-39728: fix default _missing_ so a duplicate ValueError is not set as the __context__ of the original ValueError

  • bpo-39244: Fixed multiprocessing.context.get_all_start_methods to properly return the default method first on macOS.

  • bpo-39040: Fix parsing of invalid mime headers parameters by collapsing whitespace between encoded words in a bare-quote-string.

  • bpo-38731: Add --quiet option to command-line interface of py_compile. Patch by Gregory Schevchenko.

  • bpo-35714: struct.error is now raised if there is a null character in a struct format string.

  • bpo-38144: Added the root_dir and dir_fd parameters in glob.glob().

  • bpo-26543: Fix IMAP4.noop() when debug mode is enabled (ex: imaplib.Debug = 3).

  • bpo-12178: csv.writer() now correctly escapes escapechar when input contains escapechar. Patch by Catalin Iacob, Berker Peksag, and Itay Elbirt.

  • bpo-36290: AST nodes are now raising TypeError on conflicting keyword arguments. Patch contributed by Rémi Lapeyre.

  • bpo-33944: Added site-packages tracing in verbose mode.

  • bpo-35078: Refactor formatweekday, formatmonthname methods in LocaleHTMLCalendar and LocaleTextCalendar classes in calendar module to call the base class methods.This enables customizable CSS classes for LocaleHTMLCalendar. Patch by Srinivas Reddy Thatiparthy

  • bpo-29620: assertWarns() no longer raises a RuntimeException when accessing a module's __warningregistry__ causes importation of a new module, or when a new module is imported in another thread. Patch by Kernc.

  • bpo-31844: Remove ParserBase.error() method from the private and undocumented _markupbase module. html.parser.HTMLParser is the only subclass of ParserBase and its error() implementation was deprecated in Python 3.4 and removed in Python 3.5.

  • bpo-34226: Fix cgi.parse_multipart without content_length. Patch by Roger Duran

  • bpo-33660: Fix pathlib.PosixPath to resolve a relative path located on the root directory properly.

  • bpo-28557: Improve the error message for a misbehaving rawio.readinto

  • bpo-26680: The d.is_integer() method is added to the Decimal type, for compatibility with other number types.

  • bpo-26680: The x.is_integer() method is incorporated into the abstract types of the numeric tower, Real, Rational and Integral, with appropriate default implementations.


  • bpo-41428: Add documentation for PEP 604 (Allow writing union types as X | Y).

  • bpo-41774: In Programming FAQ "Sequences (Tuples/Lists)" section, add "How do you remove multiple items from a list".

  • bpo-35293: Fix RemovedInSphinx40Warning when building the documentation. Patch by Dong-hee Na.

  • bpo-37149: Change Shipman tkinter doc link from to TkDocs. (The doc has been removed from the NMT server.) The new link responds much faster and includes a short explanatory note.

  • bpo-41726: Update the refcounts info of PyType_FromModuleAndSpec.

  • bpo-41624: Fix the signature of typing.Coroutine.

  • bpo-40204: Enable Sphinx 3.2 c_allow_pre_v3 option and disable c_warn_on_allowed_pre_v3 option to make the documentation compatible with Sphinx 2 and Sphinx 3.

  • bpo-41045: Add documentation for debug feature of f-strings.

  • bpo-41314: Changed the release when from __future__ import annotations becomes the default from 4.0 to 3.10 (following a change in PEP 563).

  • bpo-40979: Refactored typing.rst, arranging more than 70 classes, functions, and decorators into new sub-sections.

  • bpo-40552: Fix in tutorial section 4.2. Code snippet is now correct.

  • bpo-39883: Make code, examples, and recipes in the Python documentation be licensed under the more permissive BSD0 license in addition to the existing Python 2.0 license.

  • bpo-37703: Updated Documentation to comprehensively elaborate on the behaviour of gather.cancel()


  • bpo-41939: Fix test_site.test_license_exists_at_url(): call urllib.request.urlcleanup() to reset the global urllib.request._opener. Patch by Victor Stinner.

  • bpo-41731: Make test_cmd_line_script pass with option '-vv'.

  • bpo-41602: Add tests for SIGINT handling in the runpy module.

  • bpo-41521: Rename blacklist parameter of check__all__() to not_exported.

  • bpo-41477: Make ctypes optional in test_genericalias.

  • bpo-41085: Fix integer overflow in the array.array.index() method on 64-bit Windows for index larger than 2**31.

  • bpo-41069: and the current directory for tests when run via test.regrtest contain now non-ascii characters if possible.

  • bpo-38377: On Linux, skip tests using multiprocessing if the current user cannot create a file in /dev/shm/ directory. Add the skip_if_broken_multiprocessing_synchronize() function to the module.

  • bpo-41009: Fix use of support.require_{linux|mac|freebsd}_version() decorators as class decorator.

  • bpo-41003: Fix test_copyreg when numpy is installed: test.pickletester now saves/restores warnings filters when importing numpy, to ignore filters installed by numpy.

  • bpo-40964: Disable remote imaplib tests, host is blocking incoming connections.

  • bpo-40927: Fix test_binhex when run twice: it now uses import_fresh_module() to ensure that it raises DeprecationWarning each time.

  • bpo-17258: Skip some multiprocessing tests when MD5 hash digest is blocked.

  • bpo-31904: Increase LOOPBACK_TIMEOUT to 10 for VxWorks RTOS.

  • bpo-38169: Increase code coverage for SharedMemory and ShareableList

  • bpo-34401: Make test_gdb properly run on HP-UX. Patch by Michael Osipov.


  • bpo-38249: Update Py_UNREACHABLE to use __builtin_unreachable() if only the compiler is able to use it. Patch by Dong-hee Na.

  • bpo-41617: Fix pycore_bitutils.h header file to support old clang versions: __builtin_bswap16() is not available in LLVM clang 3.0.

  • bpo-40204: Pin Sphinx version to 2.3.1 in Doc/Makefile.

  • bpo-36020: The C99 functions snprintf() and vsnprintf() are now required to build Python.

  • bpo-40684: make install now uses the PLATLIBDIR variable for the destination lib-dynload/ directory when ./configure --with-platlibdir is used.

  • bpo-40683: Fixed an issue where the zoneinfo module and its tests were not included when Python is installed with make.


  • bpo-41744: Fixes automatic import of props file when using the Nuget package.

  • bpo-41627: The user site directory for 32-bit now includes a -32 suffix to distinguish it from the 64-bit interpreter's directory.

  • bpo-41526: Fixed layout of final page of the installer by removing the special thanks to Mark Hammond (with his permission).

  • bpo-41492: Fixes the description that appears in UAC prompts.

  • bpo-40948: Improve post-install message to direct people to the "py" command.

  • bpo-41412: The installer will now fail to install on Windows 7 and Windows 8. Further, the UCRT dependency is now always downloaded on demand.

  • bpo-40741: Update Windows release to include SQLite 3.32.3.

  • bpo-41142: msilib now supports creating CAB files with non-ASCII file path and adding files with non-ASCII file path to them.

  • bpo-41074: Fixed support of non-ASCII names in functions msilib.OpenDatabase() and msilib.init_database() and non-ASCII SQL in method msilib.Database.OpenView().

  • bpo-41039: Stable ABI redirection DLL (python3.dll) now uses #pragma comment(linker) for re-exporting.

  • bpo-40164: Updates Windows OpenSSL to 1.1.1g

  • bpo-39631: Changes the registered MIME type for .py files on Windows to text/x-python instead of text/plain.

  • bpo-40677: Manually define IO_REPARSE_TAG_APPEXECLINK in case some old Windows SDK doesn't have it.

  • bpo-37556: Extend py.exe help to mention overrides via venv, shebang, environmental variables & ini files.


  • bpo-41557: Update macOS installer to use SQLite 3.33.0.

  • bpo-39580: Avoid opening Finder window if running installer from the command line. Patch contributed by Rick Heil.

  • bpo-41100: Fix configure error when building on macOS 11. Note that the current Python release was released shortly after the first developer preview of macOS 11 (Big Sur); there are other known issues with building and running on the developer preview. Big Sur is expected to be fully supported in a future bugfix release of Python 3.8.x and with 3.9.0.

  • bpo-40741: Update macOS installer to use SQLite 3.32.3.

  • bpo-41005: fixed an XDG settings issue not allowing macos to open browser in

  • bpo-40741: Update macOS installer to use SQLite 3.32.2.


  • bpo-41775: Use 'IDLE Shell' as shell title

  • bpo-35764: Rewrite the Calltips doc section.

  • bpo-40181: In calltips, stop reminding that '/' marks the end of positional-only arguments.

  • bpo-41468: Improve IDLE run crash error message (which users should never see).

  • bpo-41373: Save files loaded with no line ending, as when blank, or different line endings, by setting its line ending to the system default. Fix regression in 3.8.4 and 3.9.0b4.

  • bpo-41300: Save files with non-ascii chars. Fix regression released in 3.9.0b4 and 3.8.4.

  • bpo-37765: Add keywords to module name completion list. Rewrite Completions section of IDLE doc.

  • bpo-41152: The encoding of stdin, stdout and stderr in IDLE is now always UTF-8.

  • bpo-41144: Make Open Module open a special module such as os.path.

  • bpo-39885: Make context menu Cut and Copy work again when right-clicking within a selection.

  • bpo-40723: Make test_idle pass when run after import.


  • bpo-41936: Removed undocumented macros Py_ALLOW_RECURSION and Py_END_ALLOW_RECURSION and the recursion_critical field of the PyInterpreterState structure.

  • bpo-41692: The PyUnicode_InternImmortal() function is now deprecated and will be removed in Python 3.12: use PyUnicode_InternInPlace() instead. Patch by Victor Stinner.

  • bpo-41842: Add PyCodec_Unregister() function to unregister a codec search function.

  • bpo-41834: Remove the _Py_CheckRecursionLimit variable: it has been replaced by ceval.recursion_limit of the PyInterpreterState structure. Patch by Victor Stinner.

  • bpo-41689: Types created with PyType_FromSpec() now make any signature in their tp_doc slot accessible from __text_signature__.

  • bpo-41524: Fix bug in PyOS_mystrnicmp and PyOS_mystricmp that incremented pointers beyond the end of a string.

  • bpo-41324: Add a minimal decimal capsule API. The API supports fast conversions between Decimals up to 38 digits and their triple representation as a C struct.

  • bpo-30155: Add PyDateTime_DATE_GET_TZINFO() and PyDateTime_TIME_GET_TZINFO() macros for accessing the tzinfo attributes of datetime.datetime and datetime.time objects.

  • bpo-40170: Revert PyType_HasFeature() change: it reads again directly the PyTypeObject.tp_flags member when the limited C API is not used, rather than always calling PyType_GetFlags() which hides implementation details.

  • bpo-41123: Remove PyUnicode_AsUnicodeCopy.

  • bpo-41123: Removed PyLong_FromUnicode().

  • bpo-41123: Removed PyUnicode_GetMax().

  • bpo-41123: Removed Py_UNICODE_str* functions manipulating Py_UNICODE* strings.

  • bpo-41103: PyObject_AsCharBuffer(), PyObject_AsReadBuffer(), PyObject_CheckReadBuffer(), and PyObject_AsWriteBuffer() are removed. Please migrate to new buffer protocol; PyObject_GetBuffer() and PyBuffer_Release().

  • bpo-36346: Raises DeprecationWarning for PyUnicode_FromUnicode(NULL, size) and PyUnicode_FromStringAndSize(NULL, size) with size > 0.

  • bpo-36346: Mark Py_UNICODE_COPY, Py_UNICODE_FILL, PyUnicode_WSTR_LENGTH, PyUnicode_FromUnicode, PyUnicode_AsUnicode, and PyUnicode_AsUnicodeAndSize as deprecated in C. Remove Py_UNICODE_MATCH which was deprecated and broken since Python 3.3.

  • bpo-40989: The PyObject_INIT() and PyObject_INIT_VAR() macros become aliases to, respectively, PyObject_Init() and PyObject_InitVar() functions.

  • bpo-36020: On Windows, #include "pyerrors.h" no longer defines snprintf and vsnprintf macros.

  • bpo-40943: The PY_SSIZE_T_CLEAN macro must now be defined to use PyArg_ParseTuple() and Py_BuildValue() formats which use #: es#, et#, s#, u#, y#, z#, U# and Z#. See Parsing arguments and building values and the PEP 353.

  • bpo-40910: Export explicitly the Py_GetArgcArgv() function to the C API and document the function. Previously, it was exported implicitly which no longer works since Python is built with -fvisibility=hidden.

  • bpo-40724: Allow defining buffer slots in type specs.

  • bpo-40679: Fix a _PyEval_EvalCode() crash if qualname argument is NULL.

  • bpo-40839: Calling PyDict_GetItem() without GIL held had been allowed for historical reason. It is no longer allowed.

  • bpo-40826: PyOS_InterruptOccurred() now fails with a fatal error if it is called with the GIL released.

  • bpo-40792: The result of PyNumber_Index() now always has exact type int. Previously, the result could have been an instance of a subclass of int.

  • bpo-39573: Convert Py_REFCNT() and Py_SIZE() macros to static inline functions. They cannot be used as l-value anymore: use Py_SET_REFCNT() and Py_SET_SIZE() to set an object reference count and size. This change is backward incompatible on purpose, to prepare the C API for an opaque PyObject structure.

  • bpo-40703: The PyType_FromSpec*() functions no longer overwrite the type's "__module__" attribute if it is set via "Py_tp_members" or "Py_tp_getset".

  • bpo-39583: Remove superfluous "extern C" declarations from Include/cpython/*.h.

Python 3.9.0 beta 1

Release date: 2020-05-19


Core and Builtins

  • bpo-40663: Correctly generate annotations where parentheses are omitted but required (e.g: Type[(str, int, *other))].

  • bpo-40596: Fixed str.isidentifier() for non-canonicalized strings containing non-BMP characters on Windows.

  • bpo-40593: Improved syntax errors for invalid characters in source code.

  • bpo-40585: Fixed a bug when using codeop.compile_command() that was causing exceptions to be swallowed with the new parser. Patch by Pablo Galindo

  • bpo-40566: Apply PEP 573 to abc.

  • bpo-40502: Initialize n->n_col_offset. (Patch by Joannah Nanjekye)

  • bpo-40527: Fix command line argument parsing: no longer write errors multiple times into stderr.

  • bpo-1635741: Port errno to multiphase initialization (PEP 489).

  • bpo-40523: Add pass-throughs for hash() and reversed() to weakref.proxy objects. Patch by Pablo Galindo.

  • bpo-1635741: Port syslog to multiphase initialization (PEP 489).

  • bpo-40246: Reporting a specialised error message for invalid string prefixes, which was introduced in bpo-40246, is being reverted due to backwards compatibility concerns for strings that immediately follow a reserved keyword without whitespace between them. Constructs like bg="#d00" if clear else"#fca" were failing to parse, which is not an acceptable breakage on such short notice.

  • bpo-40417: Fix imp module deprecation warning when PyImport_ReloadModule is called. Patch by Robert Rouhani.

  • bpo-40408: Fixed support of nested type variables in GenericAlias (e.g. list[list[T]]).

  • bpo-1635741: Port _stat module to multiphase initialization (PEP 489).

  • bpo-29587: Enable implicit exception chaining when calling generator.throw().

  • bpo-40328: Add tools for generating mappings headers for CJKCodecs.

  • bpo-40228: Setting frame.f_lineno is now robust w.r.t. changes in the source-to-bytecode compiler

  • bpo-38880: Added the ability to list interpreters associated with channel ends in the internal subinterpreters module.

  • bpo-37986: Improve performance of PyLong_FromDouble() for values that fit into long.


  • bpo-40662: Fixed ast.get_source_segment() for ast nodes that have incomplete location information. Patch by Irit Katriel.

  • bpo-40665: Convert bisect to use Argument Clinic.

  • bpo-40536: Added the available_timezones() function to the zoneinfo module. Patch by Paul Ganssle.

  • bpo-40645: The hmac.HMAC exposes internal implementation details. The attributes digest_cons, inner, and outer are deprecated and will be removed in the future.

  • bpo-40645: The internal module _hashlib wraps and exposes OpenSSL's HMAC API. The new code will be used in Python 3.10 after the internal implementation details of the pure Python HMAC module are no longer part of the public API.

  • bpo-40637: Builtin hash modules can now be disabled or selectively enabled with configure --with-builtin-hashlib-hashes=sha3,blake1 or --without-builtin-hashlib-hashes.

  • bpo-37630: The hashlib module can now use SHA3 hashes and SHAKE XOF from OpenSSL when available.

  • bpo-40479: The hashlib now compiles with OpenSSL 3.0.0-alpha2.

  • bpo-40257: Revert changes to inspect.getdoc().

  • bpo-40607: When cancelling a task due to timeout, asyncio.wait_for() will now propagate the exception if an error happens during cancellation. Patch by Roman Skurikhin.

  • bpo-40612: Fix edge cases in SyntaxError formatting. If the offset is <= 0, no caret is printed. If the offset is > line length, the caret is printed pointing just after the last character.

  • bpo-40597: If text content lines are longer than policy.max_line_length, always use a content-encoding to make sure they are wrapped.

  • bpo-40571: Added functools.cache() as a simpler, more discoverable way to access the unbounded cache variant of lru_cache(maxsize=None).

  • bpo-40503: PEP 615, the zoneinfo module. Adds support for the IANA time zone database.

  • bpo-40397: Removed attributes __args__ and __parameters__ from special generic aliases like typing.List (not subscripted).

  • bpo-40549: Convert posixmodule.c ("posix" or "nt" module) to the multiphase initialization (PEP 489).

  • bpo-31033: Add a msg argument to Future.cancel() and Task.cancel().

  • bpo-40541: Added an optional counts parameter to random.sample().

  • bpo-40515: The ssl and hashlib modules now actively check that OpenSSL is build with thread support. Python 3.7.0 made thread support mandatory and no longer works safely with a no-thread builds.

  • bpo-31033: When a asyncio.Task is cancelled, the exception traceback now chains all the way back to where the task was first interrupted.

  • bpo-40504: functools.lru_cache() objects can now be the targets of weakrefs.

  • bpo-40559: Fix possible memory leak in the C implementation of asyncio.Task.

  • bpo-40480: fnmatch.fnmatch() could take exponential time in the presence of multiple * pattern characters. This was repaired by generating more elaborate regular expressions to avoid futile backtracking.

  • bpo-40495: compileall is now able to use hardlinks to prevent duplicates in a case when .pyc files for different optimization levels have the same content.

  • bpo-40457: The ssl module now support OpenSSL builds without TLS 1.0 and 1.1 methods.

  • bpo-40355: Improve error reporting in ast.literal_eval() in the presence of malformed ast.Dict nodes instead of silently ignoring any non-conforming elements. Patch by Curtis Bucher.

  • bpo-40465: Deprecated the optional random argument to random.shuffle().

  • bpo-40459: platform.win32_ver() now produces correct ptype strings instead of empty strings.

  • bpo-39435: The first argument of pickle.loads() is now positional-only.

  • bpo-39305: Update nntplib to merge nntplib.NNTP and nntplib._NNTPBase. Patch by Dong-hee Na.

  • bpo-32494: Update dbm.gnu to use gdbm_count if possible when calling len(). Patch by Dong-hee Na.

  • bpo-40453: Add isolated=True keyword-only parameter to _xxsubinterpreters.create(). An isolated subinterpreter cannot spawn threads, spawn a child process or call os.fork().

  • bpo-40286: Remove _random.Random.randbytes(): the C implementation of randbytes(). Implement the method in Python to ease subclassing: randbytes() now directly reuses getrandbits().

  • bpo-40394: Added default arguments to difflib.SequenceMatcher.find_longest_match().

  • bpo-39995: Fix a race condition in concurrent.futures._ThreadWakeup: access to _ThreadWakeup is now protected with the shutdown lock.

  • bpo-30966: Process.shutdown(wait=True) of concurrent.futures now closes explicitly the result queue.

  • bpo-30966: Add a new close() method to the SimpleQueue class to explicitly close the queue.

  • bpo-39966: Revert bpo-25597. unittest.mock.MagicMock with wraps' set uses default return values for magic methods.

  • bpo-39791: Added files() function to importlib.resources with support for subdirectories in package data, matching backport in importlib_resources 1.5.

  • bpo-40375: imaplib.IMAP4.unselect() is added. Patch by Dong-hee Na.

  • bpo-40389: repr() now returns typing.Optional[T] when called for typing.Union of two types, one of which is NoneType.

  • bpo-40291: Add support for CAN_J1939 sockets (available on Linux 5.4+)

  • bpo-40273: types.MappingProxyType is now reversible.

  • bpo-39075: The repr for types.SimpleNamespace is now insertion ordered rather than alphabetical.

  • bpo-40192: On AIX, thread_time() is now implemented with thread_cputime() which has nanosecond resolution, rather than clock_gettime(CLOCK_THREAD_CPUTIME_ID) which has a resolution of 10 ms. Patch by Batuhan Taskaya.

  • bpo-40025: Raise TypeError when _generate_next_value_ is defined after members. Patch by Ethan Onstott.

  • bpo-39058: In the argparse module, the repr for Namespace() and other argument holders now displayed in the order attributes were added. Formerly, it displayed in alphabetical order even though argument order is preserved the user visible parts of the module.

  • bpo-24416: The isocalendar() methods of and datetime.datetime now return a named tuple instead of a tuple.


  • bpo-34790: Add version of removal for explicit passing of coros to asyncio.wait()'s documentation

  • bpo-40561: Provide docstrings for webbrowser open functions.

  • bpo-40499: Mention that asyncio.wait() requires a non-empty set of awaitables.

  • bpo-39705: Tutorial example for sorted() in the Loop Techniques section is given a better explanation. Also a new example is included to explain sorted()'s basic behavior.

  • bpo-39435: Fix an incorrect signature for pickle.loads() in the docs


  • bpo-40055: distutils.tests now saves/restores warnings filters to leave them unchanged. Importing tests imports docutils which imports pkg_resources which adds a warnings filter.

  • bpo-40436: test_gdb and test.pythoninfo now check gdb command exit code.


  • bpo-40653: Move _dirnameW out of HAVE_SYMLINK to fix a potential compiling issue.

  • bpo-40514: Add --with-experimental-isolated-subinterpreters build option to configure: better isolate subinterpreters, experimental build mode.


  • bpo-40650: Include winsock2.h in pytime.c for timeval.

  • bpo-40458: Increase reserved stack space to prevent overflow crash on Windows.

  • bpo-39148: Add IPv6 support to asyncio datagram endpoints in ProactorEventLoop. Change the raised exception for unknown address families to ValueError as it's not coming from Windows API.


  • bpo-34956: When building Python on macOS from source, _tkinter now links with non-system Tcl and Tk frameworks if they are installed in /Library/Frameworks, as had been the case on older releases of macOS. If a macOS SDK is explicitly configured, by using --enable-universalsdk= or -isysroot, only the SDK itself is searched. The default behavior can still be overridden with --with-tcltk-includes and --with-tcltk-libs.

  • bpo-35569: Expose RFC 3542 IPv6 socket options.


  • bpo-40479: Update multissltest helper to test with latest OpenSSL 1.0.2, 1.1.0, 1.1.1, and 3.0.0-alpha.

  • bpo-40431: Fix a syntax typo in turtledemo that now raises a SyntaxError.

  • bpo-40163: Fix multissltest tool. OpenSSL has changed download URL for old releases. The multissltest tool now tries to download from current and old download URLs.


  • bpo-39465: Remove the _PyUnicode_ClearStaticStrings() function from the C API.

  • bpo-38787: Add PyCFunction_CheckExact() macro for exact type checks now that we allow subtypes of PyCFunction, as well as PyCMethod_CheckExact() and PyCMethod_Check() for the new PyCMethod subtype.

  • bpo-40545: Declare _PyErr_GetTopmostException() with PyAPI_FUNC() to properly export the function in the C API. The function remains private (_Py) prefix.

  • bpo-40412: Nullify inittab_copy during finalization, preventing future interpreter initializations in an embedded situation from crashing. Patch by Gregory Szorc.

  • bpo-40429: The PyThreadState_GetFrame() function now returns a strong reference to the frame.

  • bpo-40428: Remove the following functions from the C API. Call PyGC_Collect() explicitly to free all free lists.

    • PyAsyncGen_ClearFreeLists()

    • PyContext_ClearFreeList()

    • PyDict_ClearFreeList()

    • PyFloat_ClearFreeList()

    • PyFrame_ClearFreeList()

    • PyList_ClearFreeList()

    • PySet_ClearFreeList()

    • PyTuple_ClearFreeList()

  • bpo-40421: New PyFrame_GetBack() function: get the frame next outer frame.

  • bpo-40421: New PyFrame_GetCode() function: return a borrowed reference to the frame code.

  • bpo-40217: Ensure that instances of types created with PyType_FromSpecWithBases() will visit its class object when traversing references in the garbage collector (implemented as an extension of the provided tp_traverse). Patch by Pablo Galindo.

  • bpo-38787: Module C state is now accessible from C-defined heap type methods (PEP 573). Patch by Marcel Plch and Petr Viktorin.

Python 3.9.0 alpha 6

Release date: 2020-04-27


  • bpo-40121: Fixes audit events raised on creating a new socket.

  • bpo-39073: Disallow CR or LF in email.headerregistry.Address arguments to guard against header injection attacks.

  • bpo-39503: CVE-2020-8492: The AbstractBasicAuthHandler class of the urllib.request module uses an inefficient regular expression which can be exploited by an attacker to cause a denial of service. Fix the regex to prevent the catastrophic backtracking. Vulnerability reported by Ben Caller and Matt Schwager.

Core and Builtins

  • bpo-40313: Improve the performance of bytes.hex().

  • bpo-40334: Switch to a new parser, based on PEG. For more details see PEP 617. To temporarily switch back to the old parser, use -X oldparser or PYTHONOLDPARSER=1. In Python 3.10 we will remove the old parser completely, including the parser module (already deprecated) and anything that depends on it.

  • bpo-40267: Fix the tokenizer to display the correct error message, when there is a SyntaxError on the last input character and no newline follows. It used to be unexpected EOF while parsing, while it should be invalid syntax.

  • bpo-39522: Correctly unparse explicit u prefix for strings when postponed evaluation for annotations activated. Patch by Batuhan Taskaya.

  • bpo-40246: Report a specialized error message, invalid string prefix, when the tokenizer encounters a string with an invalid prefix.

  • bpo-40082: Fix the signal handler: it now always uses the main interpreter, rather than trying to get the current Python thread state.

  • bpo-37388: str.encode() and str.decode() no longer check the encoding and errors in development mode or in debug mode during Python finalization. The codecs machinery can no longer work on very late calls to str.encode() and str.decode().

  • bpo-40077: Fix possible refleaks in _json, memo of PyScannerObject should be traversed.

  • bpo-37207: Speed up calls to dict() by using the PEP 590 vectorcall calling convention.

  • bpo-40141: Add column and line information to ast.keyword nodes. Patch by Pablo Galindo.

  • bpo-1635741: Port resource to multiphase initialization (PEP 489).

  • bpo-1635741: Port math to multiphase initialization (PEP 489).

  • bpo-1635741: Port _uuid module to multiphase initialization (PEP 489).

  • bpo-40077: Convert json module to use PyType_FromSpec().

  • bpo-40067: Improve the error message for multiple star expressions in an assignment. Patch by Furkan Onder

  • bpo-1635741: Port _functools module to multiphase initialization (PEP 489). Patch by Paulo Henrique Silva.

  • bpo-1635741: Port operator module to multiphase initialization (PEP 489). Patch by Paulo Henrique Silva.

  • bpo-20526: Fix PyThreadState_Clear(). PyThreadState.frame is a borrowed reference, not a strong reference: PyThreadState_Clear() must not call Py_CLEAR(tstate->frame).

  • bpo-1635741: Port time module to multiphase initialization (PEP 489). Patch by Paulo Henrique Silva.

  • bpo-1635741: Port _weakref extension module to multiphase initialization (PEP 489).

  • bpo-40020: Fix a leak and subsequent crash in parsetok.c caused by realloc misuse on a rare codepath.

  • bpo-39939: Added str.removeprefix and str.removesuffix methods and corresponding bytes, bytearray, and collections.UserString methods to remove affixes from a string if present. See PEP 616 for a full description. Patch by Dennis Sweeney.

  • bpo-39481: Implement PEP 585. This supports list[int], tuple[str, ...] etc.

  • bpo-32894: Support unparsing of infinity numbers in postponed annotations. Patch by Batuhan Taşkaya.

  • bpo-37207: Speed up calls to list() by using the PEP 590 vectorcall calling convention. Patch by Mark Shannon.


  • bpo-40398: typing.get_args() now always returns an empty tuple for special generic aliases.

  • bpo-40396: Functions typing.get_origin(), typing.get_args() and typing.get_type_hints() support now generic aliases like list[int].

  • bpo-38061: Optimize the subprocess module on FreeBSD using closefrom(). A single close(fd) syscall is cheap, but when sysconf(_SC_OPEN_MAX) is high, the loop calling close(fd) on each file descriptor can take several milliseconds.

    The workaround on FreeBSD to improve performance was to load and mount the fdescfs kernel module, but this is not enabled by default.

    Initial patch by Ed Maste (emaste), Conrad Meyer (cem), Kyle Evans (kevans) and Kubilay Kocak (koobs):

  • bpo-38061: On FreeBSD, os.closerange(fd_low, fd_high) now calls closefrom(fd_low) if fd_high is greater than or equal to sysconf(_SC_OPEN_MAX).

    Initial patch by Ed Maste (emaste), Conrad Meyer (cem), Kyle Evans (kevans) and Kubilay Kocak (koobs):

  • bpo-40360: The lib2to3 module is pending deprecation due to PEP 617.

  • bpo-40138: Fix the Windows implementation of os.waitpid() for exit code larger than INT_MAX >> 8. The exit status is now interpreted as an unsigned number.

  • bpo-39942: Set "__main__" as the default module name when "__name__" is missing in typing.TypeVar. Patch by Weipeng Hong.

  • bpo-40275: The logging package is now imported lazily in unittest only when the assertLogs() assertion is used.

  • bpo-40275: The asyncio package is now imported lazily in unittest only when the IsolatedAsyncioTestCase class is used.

  • bpo-40330: In ShareableList.__setitem__(), check the size of a new string item after encoding it to utf-8, not before.

  • bpo-40148: Added pathlib.Path.with_stem() to create a new Path with the stem replaced.

  • bpo-40325: Deprecated support for set objects in random.sample().

  • bpo-40257: Improved help for the typing module. Docstrings are now shown for all special forms and special generic aliases (like Union and List). Using help() with generic alias like List[int] will show the help for the correspondent concrete type (list in this case).

  • bpo-40257: func:inspect.getdoc no longer returns docstring inherited from the type of the object or from parent class if it is a class if it is not defined in the object itself. In pydoc the documentation string is now shown not only for class, function, method etc, but for any object that has its own __doc__ attribute.

  • bpo-40287: Fixed to return the position.

  • bpo-40290: Added zscore() to statistics.NormalDist().

  • bpo-40282: Allow random.getrandbits(0) to succeed and to return 0.

  • bpo-40286: Add random.randbytes() function and random.Random.randbytes() method to generate random bytes.

  • bpo-40277: collections.namedtuple() now provides a human-readable repr for its field accessors.

  • bpo-40270: The included copy of sqlite3 on Windows is now compiled with the json extension. This allows the use of functions such as json_object.

  • bpo-29255: Wait in when no fds are registered

  • bpo-40260: Ensure modulefinder uses io.open_code() and respects coding comments.

  • bpo-40234: Allow again to spawn daemon threads in subinterpreters (revert change which denied them).

  • bpo-39207: Workers in ProcessPoolExecutor are now spawned on demand, only when there are no available idle workers to reuse. This optimizes startup overhead and reduces the amount of lost CPU time to idle workers. Patch by Kyle Stanley.

  • bpo-40091: Fix a hang at fork in the logging module: the new private _at_fork_reinit() method is now used to reinitialize locks at fork in the child process.

  • bpo-40149: Implement traverse and clear slots in _abc._abc_data type.

  • bpo-40208: Remove deprecated symtable.SymbolTable.has_exec().

  • bpo-40196: Fix a bug in the symtable module that was causing incorrectly report global variables as local. Patch by Pablo Galindo.

  • bpo-40190: Add support for _SC_AIX_REALMEM to posix.sysconf().

  • bpo-40182: Removed the _field_types attribute of the typing.NamedTuple class.

  • bpo-36517: Multiple inheritance with typing.NamedTuple now raises an error instead of silently ignoring other types.

  • bpo-40126: Fixed reverting multiple patches in unittest.mock. Patcher's __exit__() is now never called if its __enter__() is failed. Returning true from __exit__() silences now the exception.

  • bpo-40094: CGIHTTPRequestHandler of http.server now logs the CGI script exit code, rather than the CGI script exit status of os.waitpid(). For example, if the script is killed by signal 11, it now logs: "CGI script exit code -11."

  • bpo-40108: Improve the error message when triying to import a module using runpy and incorrently use the ".py" extension at the end of the module name. Patch by Pablo Galindo.

  • bpo-40094: Add os.waitstatus_to_exitcode() function: convert a wait status to an exit code.

  • bpo-40089: Fix threading._after_fork(): if fork was not called by a thread spawned by threading.Thread, threading._after_fork() now creates a _MainThread instance for _main_thread, instead of a _DummyThread instance.

  • bpo-40089: Add a private _at_fork_reinit() method to _thread.Lock, _thread.RLock, threading.RLock and threading.Condition classes: reinitialize the lock at fork in the child process, reset the lock to the unlocked state. Rename also the private _reset_internal_locks() method of threading.Event to _at_fork_reinit().

  • bpo-25780: Expose CAN_RAW_JOIN_FILTERS in the socket module.

  • bpo-39503: AbstractBasicAuthHandler of urllib.request now parses all WWW-Authenticate HTTP headers and accepts multiple challenges per header: use the realm of the first Basic challenge.

  • bpo-39812: Removed daemon threads from concurrent.futures by adding an internal threading._register_atexit(), which calls registered functions prior to joining all non-daemon threads. This allows for compatibility with subinterpreters, which don't support daemon threads.

  • bpo-40050: Fix importlib._bootstrap_external: avoid creating a new winreg builtin module if it's already available in sys.modules, and remove redundant imports.

  • bpo-40014: Fix os.getgrouplist(): if getgrouplist() function fails because the group list is too small, retry with a larger group list. On failure, the glibc implementation of getgrouplist() sets ngroups to the total number of groups. For other implementations, double the group list size.

  • bpo-40017: Add time.CLOCK_TAI constant if the operating system support it.

  • bpo-40016: In re docstring, clarify the relationship between inline and argument compile flags.

  • bpo-39953: Update internal table of OpenSSL error codes in the ssl module.

  • bpo-36144: Added PEP 584 operators to weakref.WeakValueDictionary.

  • bpo-36144: Added PEP 584 operators to weakref.WeakKeyDictionary.

  • bpo-38891: Fix linear runtime behaviour of the __getitem__ and __setitem__ methods in multiprocessing.shared_memory.ShareableList. This avoids quadratic performance when iterating a ShareableList. Patch by Thomas Krennwallner.

  • bpo-39682: Remove undocumented support for closing a pathlib.Path object via its context manager. The context manager magic methods remain, but they are now a no-op, making Path objects immutable.

  • bpo-36144: Added PEP 584 operators (| and |=) to collections.ChainMap.

  • bpo-39011: Normalization of line endings in ElementTree attributes was removed, as line endings which were replaced by entity numbers should be preserved in original form.

  • bpo-38410: Properly handle sys.audit() failures in sys.set_asyncgen_hooks().

  • bpo-36541: lib2to3 now recognizes named assignment expressions (the walrus operator, :=)

  • bpo-35967: In platform, delay the invocation of 'uname -p' until the processor attribute is requested.

  • bpo-35113: inspect.getsource() now returns correct source code for inner class with same name as module level class. Decorators are also returned as part of source of the class. Patch by Karthikeyan Singaravelan.

  • bpo-33262: Deprecate passing None as an argument for shlex.split()'s s parameter. Patch by Zackery Spytz.

  • bpo-31758: Prevent crashes when using an uninitialized _elementtree.XMLParser object. Patch by Oren Milman.


  • bpo-27635: The pickle documentation incorrectly claimed that __new__ isn't called by default when unpickling.

  • bpo-39879: Updated Modèle de données docs to include dict() insertion order preservation. Patch by Furkan Onder and Samy Lahfa.

  • bpo-38387: Document PyDoc_STRVAR macro in the C-API reference.

  • bpo-13743: Some methods within xml.dom.minidom.Element class are now better documented.


  • bpo-31904: Set expected default encoding in for VxWorks RTOS.

  • bpo-40162: Update Travis CI configuration to OpenSSL 1.1.1f.

  • bpo-40146: Update OpenSSL to 1.1.1f in Azure Pipelines.

  • bpo-40094: Add function.

  • bpo-40003: test.bisect_cmd now copies Python command line options like -O or -W. Moreover, emit a warning if test.bisect_cmd is used with -w/--verbose2 option.

  • bpo-39380: Add the encoding in ftplib.FTP and ftplib.FTP_TLS to the constructor as keyword-only and change the default from latin-1 to utf-8 to follow RFC 2640.

  • bpo-39793: Use the same domain when testing make_msgid. Patch by Batuhan Taskaya.

  • bpo-1812: Fix newline handling in doctest.testfile when loading from a package whose loader has a get_data method. Patch by Peter Donis.


  • bpo-38360: Support single-argument form of macOS -isysroot flag.

  • bpo-40158: Fix CPython MSBuild Properties in NuGet Package (build/native/python.props)

  • bpo-38527: Fix configure check on Solaris for "float word ordering": sometimes, the correct "grep" command was not being used. Patch by Arnon Yaari.


  • bpo-40164: Updates Windows to OpenSSL 1.1.1f

  • bpo-8901: Ignore the Windows registry when the -E option is used.


  • bpo-38329: macOS installers now update the Current version symlink of /Library/Frameworks/Python.framework/Versions for 3.9 installs. Previously, Current was only updated for Python 2.x installs. This should make it easier to embed Python 3 into other macOS applications.

  • bpo-40164: Update macOS installer builds to use OpenSSL 1.1.1g.


  • bpo-38439: Add a 256×256 pixel IDLE icon to support more modern environments. Created by Andrew Clover. Delete the unused macOS idle.icns icon file.

  • bpo-38689: IDLE will no longer freeze when inspect.signature fails when fetching a calltip.



Python 3.9.0 alpha 5

Release date: 2020-03-23


  • bpo-38576: Disallow control characters in hostnames in http.client, addressing CVE-2019-18348. Such potentially malicious header injection URLs now cause a InvalidURL to be raised.

Core and Builtins

  • bpo-40010: Optimize pending calls in multithreaded applications. If a thread different than the main thread schedules a pending call (Py_AddPendingCall()), the bytecode evaluation loop is no longer interrupted at each bytecode instruction to check for pending calls which cannot be executed. Only the main thread can execute pending calls.

    Previously, the bytecode evaluation loop was interrupted at each instruction until the main thread executes pending calls.

  • bpo-1635741: Port _weakref extension module to multiphase initialization (PEP 489).

  • bpo-1635741: Port _collections module to multiphase initialization (PEP 489).

  • bpo-40010: Optimize signal handling in multithreaded applications. If a thread different than the main thread gets a signal, the bytecode evaluation loop is no longer interrupted at each bytecode instruction to check for pending signals which cannot be handled. Only the main thread of the main interpreter can handle signals.

    Previously, the bytecode evaluation loop was interrupted at each instruction until the main thread handles signals.

  • bpo-39984: If Py_AddPendingCall() is called in a subinterpreter, the function is now scheduled to be called from the subinterpreter, rather than being called from the main interpreter. Each subinterpreter now has its own list of scheduled calls.

  • bpo-1635741: Port _heapq module to multiphase initialization.

  • bpo-1635741: Port itertools module to multiphase initialization (PEP 489).

  • bpo-37207: Speed up calls to frozenset() by using the PEP 590 vectorcall calling convention. Patch by Dong-hee Na.

  • bpo-39984: subinterpreters: Move _PyRuntimeState.ceval.tracing_possible to PyInterpreterState.ceval.tracing_possible: each interpreter now has its own variable.

  • bpo-37207: Speed up calls to set() by using the PEP 590 vectorcall calling convention. Patch by Dong-hee Na.

  • bpo-1635741: Port _statistics module to multiphase initialization (PEP 489).

  • bpo-39968: Use inline function to replace extension modules' get_module_state macros.

  • bpo-39965: Correctly raise SyntaxError if await is used inside non-async functions and PyCF_ALLOW_TOP_LEVEL_AWAIT is set (like in the asyncio REPL). Patch by Pablo Galindo.

  • bpo-39562: Allow executing asynchronous comprehensions on the top level when the PyCF_ALLOW_TOP_LEVEL_AWAIT flag is given. Patch by Batuhan Taskaya.

  • bpo-37207: Speed up calls to tuple() by using the PEP 590 vectorcall calling convention. Patch by Dong-hee Na.

  • bpo-38373: Changed list overallocation strategy. It no longer overallocates if the new size is closer to overallocated size than to the old size and adds padding.

  • bpo-39926: Update Unicode database to Unicode version 13.0.0.

  • bpo-19466: Clear the frames of daemon threads earlier during the Python shutdown to call objects destructors. So "unclosed file" resource warnings are now emitted for daemon threads in a more reliable way.

  • bpo-38894: Fix a bug that was causing incomplete results when calling pathlib.Path.glob in the presence of symlinks that point to files where the user does not have read access. Patch by Pablo Galindo and Matt Wozniski.

  • bpo-39877: Fix PyEval_RestoreThread() random crash at exit with daemon threads. It now accesses the _PyRuntime variable directly instead of using tstate->interp->runtime, since tstate can be a dangling pointer after Py_Finalize() has been called. Moreover, the daemon thread now exits before trying to take the GIL.

  • bpo-39871: Fix a possible SystemError in math.{atan2,copysign,remainder}() when the first argument cannot be converted to a float. Patch by Zackery Spytz.

  • bpo-39776: Fix race condition where threads created by PyGILState_Ensure() could get a duplicate id.

    This affects consumers of tstate->id like the contextvar caching machinery, which could return invalid cached objects under heavy thread load (observed in embedded scenarios).

  • bpo-39778: Fixed a crash due to incorrect handling of weak references in collections.OrderedDict classes. Patch by Pablo Galindo.

  • bpo-1635741: Port audioop extension module to multiphase initialization (PEP 489).

  • bpo-39702: Relax decorator grammar restrictions to allow any valid expression (PEP 614).

  • bpo-38091: Tweak import deadlock detection code to not deadlock itself.

  • bpo-1635741: Port _locale extension module to multiphase initialization (PEP 489).

  • bpo-39087: Optimize PyUnicode_AsUTF8() and PyUnicode_AsUTF8AndSize() slightly when they need to create internal UTF-8 cache.

  • bpo-39520: Fix unparsing of ext slices with no items (foo[:,]). Patch by Batuhan Taskaya.

  • bpo-39220: Do not optimize annotations if 'from __future__ import annotations' is used. Patch by Pablo Galindo.

  • bpo-35712: Using NotImplemented in a boolean context has been deprecated. Patch contributed by Josh Rosenberg.

  • bpo-22490: Don't leak environment variable __PYVENV_LAUNCHER__ into the interpreter session on macOS.


  • bpo-39830: Add zipfile.Path to __all__ in the zipfile module.

  • bpo-40000: Improved error messages for validation of ast.Constant nodes. Patch by Batuhan Taskaya.

  • bpo-39999: __module__ of the AST node classes is now set to "ast" instead of "_ast". Added docstrings for dummy AST node classes and deprecated attributes.

  • bpo-39991: uuid.getnode() now skips IPv6 addresses with the same string length than a MAC address (17 characters): only use MAC addresses.

  • bpo-39988: Deprecated ast.AugLoad and ast.AugStore node classes because they are no longer used.

  • bpo-39656: Ensure bin/python3.# is always present in virtual environments on POSIX platforms - by Anthony Sottile.

  • bpo-39969: Deprecated ast.Param node class because it's no longer used. Patch by Batuhan Taskaya.

  • bpo-39360: Ensure all workers exit when finalizing a multiprocessing.Pool implicitly via the module finalization handlers of multiprocessing. This fixes a deadlock situation that can be experienced when the Pool is not properly finalized via the context manager or a call to multiprocessing.Pool.terminate. Patch by Batuhan Taskaya and Pablo Galindo.

  • bpo-35370: sys.settrace(), sys.setprofile() and _lsprof.Profiler.enable() now properly report PySys_Audit() error if "sys.setprofile" or "sys.settrace" audit event is denied.

  • bpo-39936: AIX: Fix _aix_support module when the subprocess is not available, when building Python from scratch. It now uses new private _bootsubprocess module, rather than having two implementations depending if subprocess is available or not. So _aix_support.aix_platform() result is now the same if subprocess is available or not.

  • bpo-36144: collections.OrderedDict now implements | and |= (PEP 584).

  • bpo-39652: The column name found in sqlite3.Cursor.description is now truncated on the first '[' only if the PARSE_COLNAMES option is set.

  • bpo-39915: Ensure unittest.mock.AsyncMock.await_args_list has call objects in the order of awaited arguments instead of using unittest.mock.Mock.call_args which has the last value of the call. Patch by Karthikeyan Singaravelan.

  • bpo-36144: Updated os.environ and os.environb to support PEP 584's merge (|) and update (|=) operators.

  • bpo-38662: The ensurepip module now invokes pip via the runpy module. Hence it is no longer tightly coupled with the internal API of the bundled pip version, allowing easier updates to a newer pip version both internally and for distributors.

  • bpo-38075: Fix the random.Random.seed() method when a bool is passed as the seed.

  • bpo-39916: More reliable use of os.scandir() in Path.glob(). It no longer emits a ResourceWarning when interrupted.

  • bpo-39850: multiprocessing now supports abstract socket addresses (if abstract sockets are supported in the running platform). When creating arbitrary addresses (like when default-constructing multiprocessing.connection.Listener objects) abstract sockets are preferred to avoid the case when the temporary-file-generated address is too large for an AF_UNIX socket address. Patch by Pablo Galindo.

  • bpo-36287: ast.dump() no longer outputs optional fields and attributes with default values. The default values for optional fields and attributes of AST nodes are now set as class attributes (e.g. Constant.kind is set to None).

  • bpo-39889: Fixed ast.unparse() for extended slices containing a single element (e.g. a[i:j,]). Remove redundant tuples when index with a tuple (e.g. a[i, j]).

  • bpo-39828: Fix json.tool to catch BrokenPipeError. Patch by Dong-hee Na.

  • bpo-13487: Avoid a possible "RuntimeError: dictionary changed size during iteration" from inspect.getmodule() when it tried to loop through sys.modules.

  • bpo-39674: Revert "bpo-37330: open() no longer accept 'U' in file mode". The "U" mode of open() is kept in Python 3.9 to ease transition from Python 2.7, but will be removed in Python 3.10.

  • bpo-28577: The hosts method on 32-bit prefix length IPv4Networks and 128-bit prefix IPv6Networks now returns a list containing the single Address instead of an empty list.

  • bpo-39826: Add getConnection method to logging HTTPHandler to enable custom connections.

  • bpo-39763: Reimplement distutils.spawn.spawn() function with the subprocess module.

  • bpo-39794: Add --without-decimal-contextvar build option. This enables a thread-local rather than a coroutine local context.

  • bpo-36144: collections.defaultdict now implements | (PEP 584).

  • bpo-39517: Fix runpy.run_path() when using pathlike objects

  • bpo-39775: Change inspect.Signature.parameters back to collections.OrderedDict. This was changed to dict in Python 3.9.0a4.

  • bpo-39678: Refactor queue_manager in concurrent.futures.ProcessPoolExecutor to make it easier to maintain.

  • bpo-39764: Fix AttributeError when calling get_stack on a PyAsyncGenObject Task

  • bpo-39769: The compileall.compile_dir() function's ddir parameter and the compileall command line flag -d no longer write the wrong pathname to the generated pyc file for submodules beneath the root of the directory tree being compiled. This fixes a regression introduced with Python 3.5.

  • bpo-36144: types.MappingProxyType objects now support the merge (|) operator from PEP 584.

  • bpo-38691: The importlib module now ignores the PYTHONCASEOK environment variable when the -E or -I command line options are being used.

  • bpo-39719: Remove tempfile.SpooledTemporaryFile.softspace() as files no longer have the softspace attribute in Python 3. Patch by Shantanu.

  • bpo-39667: Improve pathlib.Path compatibility on zipfile.Path and correct performance degradation as found in zipp 3.0.

  • bpo-39638: Keep ASDL signatures in the docstrings for AST nodes. Patch by Batuhan Taskaya

  • bpo-39639: Deprecated ast.Suite node class because it's no longer used. Patch by Batuhan Taskaya.

  • bpo-39609: Add thread_name_prefix to default asyncio executor

  • bpo-39548: Fix handling of header in urllib.request.AbstractDigestAuthHandler when the optional qop parameter is not present.

  • bpo-39509: HTTP status codes 103 EARLY_HINTS and 425 TOO_EARLY are added to http.HTTPStatus. Patch by Dong-hee Na.

  • bpo-39507: Adding HTTP status 418 "I'm a Teapot" to HTTPStatus in http library. Patch by Ross Rhodes.

  • bpo-39495: Remove default value from attrs parameter of xml.etree.ElementTree.TreeBuilder.start() for consistency between Python and C implementations.

  • bpo-38971: Open issue in the BPO indicated a desire to make the implementation of at parity with, which implements a try/except to assure file stream gets closed before an exception is raised.

  • bpo-38641: Added starred expressions support to return and yield statements for lib2to3. Patch by Vlad Emelianov.

  • bpo-37534: When using minidom module to generate XML documents the ability to add Standalone Document Declaration is added. All the changes are made to generate a document in compliance with Extensible Markup Language (XML) 1.0 (Fifth Edition) W3C Recommendation (available here:

  • bpo-34788: Add support for scoped IPv6 addresses to ipaddress. Patch by Oleksandr Pavliuk.

  • bpo-34822: Simplified AST for subscription. Simple indices are now represented by their value, extended slices are represented as tuples. ast classes Index and ExtSlice are considered deprecated and will be removed in future Python versions. In the meantime, Index(value) now returns a value itself, ExtSlice(slices) returns Tuple(slices, Load()).


  • bpo-39868: Updated the Language Reference for PEP 572.

  • bpo-13790: Change 'string' to 'specification' in format doc.

  • bpo-17422: The language reference no longer restricts default class namespaces to dicts only.

  • bpo-39530: Fix misleading documentation about mixed-type numeric comparisons.

  • bpo-39718: Update token documentation to reflect additions in Python 3.8

  • bpo-39677: Changed operand name of MAKE_FUNCTION from argc to flags for module dis


  • bpo-40019: test_gdb now skips tests if it detects that gdb failed to read debug information because the Python binary is optimized.

  • bpo-27807: test_site.test_startup_imports() is now skipped if a path of sys.path contains a .pth file.

  • bpo-26067: Do not fail test_shutil test_chown test when uid or gid of user cannot be resolved to a name.

  • bpo-39855: test_subprocess.test_user() now skips the test on an user name if the user name doesn't exist. For example, skip the test if the user "nobody" doesn't exist on Linux.


  • bpo-39761: Fix build with DTrace but without additional DFLAGS.

  • bpo-39763: now uses a basic implementation of the subprocess module if the subprocess module is not available: before required C extension modules are built.

  • bpo-1294959: Add --with-platlibdir option to the configure script: name of the platform-specific library directory, stored in the new sys.platlibdir attribute. It is used to build the path of platform-specific extension modules and the path of the standard library. It is equal to "lib" on most platforms. On Fedora and SuSE, it is equal to "lib64" on 64-bit platforms. Patch by Jan Matějek, Matěj Cepl, Charalampos Stratakis and Victor Stinner.


  • bpo-39930: Ensures the required vcruntime140.dll is included in install packages.

  • bpo-39847: Avoid hang when computer is hibernated whilst waiting for a mutex (for lock-related objects from threading) around 49-day uptime.

  • bpo-38597: distutils will no longer statically link vcruntime140.dll when a redistributable version is unavailable. All future releases of CPython will include a copy of this DLL to ensure distributed extensions can continue to load.

  • bpo-38380: Update Windows builds to use SQLite 3.31.1

  • bpo-39789: Update Windows release build machines to Visual Studio 2019 (MSVC 14.2).

  • bpo-34803: Package for now includes repository reference and bundled icon image.


  • bpo-38380: Update macOS builds to use SQLite 3.31.1


  • bpo-27115: For 'Go to Line', use a Query box subclass with IDLE standard behavior and improved error checking.

  • bpo-39885: Since clicking to get an IDLE context menu moves the cursor, any text selection should be and now is cleared.

  • bpo-39852: Edit "Go to line" now clears any selection, preventing accidental deletion. It also updates Ln and Col on the status bar.

  • bpo-39781: Selecting code context lines no longer causes a jump.


  • bpo-36184: Port to FreeBSD. now checks for "take_gil" function name to check if a frame tries to acquire the GIL, instead of checking for "pthread_cond_timedwait" which is specific to Linux and can be a different condition than the GIL.

  • bpo-38080: Added support to fix getproxies in the lib2to3.fixes.fix_urllib module. Patch by José Roberto Meza Cabrera.


Python 3.9.0 alpha 4

Release date: 2020-02-25


Core and Builtins

  • bpo-39382: Fix a use-after-free in the single inheritance path of issubclass(), when the __bases__ of an object has a single reference, and so does its first item. Patch by Yonatan Goldschmidt.

  • bpo-39573: Update clinic tool to use Py_IS_TYPE(). Patch by Dong-hee Na.

  • bpo-39619: Enable use of os.chroot() on HP-UX systems.

  • bpo-39573: Add Py_IS_TYPE() static inline function to check whether the object o type is type.

  • bpo-39606: Fix regression caused by fix for bpo-39386, that prevented calling aclose on an async generator that had already been closed or exhausted.

  • bpo-39579: Change the ending column offset of Attribute nodes constructed in ast_for_dotted_name to point at the end of the current node and not at the end of the last NAME node.

  • bpo-1635741: Port _crypt extension module to multiphase initialization (PEP 489).

  • bpo-1635741: Port _contextvars extension module to multiphase initialization (PEP 489).

  • bpo-39510: Fix segfault in readinto() method on closed BufferedReader.

  • bpo-39502: Fix time.localtime() on 64-bit AIX to support years before 1902 and after 2038. Patch by M Felt.

  • bpo-39492: Fix a reference cycle in the C Pickler that was preventing the garbage collection of deleted, pickled objects.

  • bpo-39453: Fixed a possible crash in list.__contains__() when a list is changed during comparing items. Patch by Dong-hee Na.

  • bpo-39434: floor division of float operation now has a better performance. Also the message of ZeroDivisionError for this operation is updated. Patch by Dong-hee Na.

  • bpo-1635741: Port _codecs extension module to multiphase initialization (PEP 489).

  • bpo-1635741: Port _bz2 extension module to multiphase initialization (PEP 489).

  • bpo-1635741: Port _abc extension module to multiphase initialization (PEP 489).

  • bpo-39320: Replace two complex bytecodes for building dicts with two simpler ones. The new bytecodes DICT_MERGE and DICT_UPDATE have been added The old bytecodes BUILD_MAP_UNPACK and BUILD_MAP_UNPACK_WITH_CALL have been removed.

  • bpo-39219: Syntax errors raised in the tokenizer now always set correct "text" and "offset" attributes.

  • bpo-36051: Drop the GIL during large bytes.join operations. Patch by Bruce Merry.

  • bpo-38960: Fix DTrace build issues on FreeBSD. Patch by David Carlier.

  • bpo-37207: Speed up calls to range() by about 30%, by using the PEP 590 vectorcall calling convention. Patch by Mark Shannon.

  • bpo-36144: dict (and collections.UserDict) objects now support PEP 584's merge (|) and update (|=) operators. Patch by Brandt Bucher.

  • bpo-32856: Optimized the idiom for assignment a temporary variable in comprehensions. Now for y in [expr] in comprehensions is as fast as a simple assignment y = expr.


  • bpo-30566: Fix IndexError when trying to decode an invalid string with punycode codec.

  • bpo-39649: Remove obsolete check for __args__ in bdb.Bdb.format_stack_entry.

  • bpo-39648: Expanded math.gcd() and math.lcm() to handle multiple arguments.

  • bpo-39681: Fix a regression where the C pickle module wouldn't allow unpickling from a file-like object that doesn't expose a readinto() method.

  • bpo-35950: Raise io.UnsupportedOperation in io.BufferedReader.truncate() when it is called on a read-only io.BufferedReader instance.

  • bpo-39479: Add math.lcm() function: least common multiple.

  • bpo-39674: Revert "Do not expose abstract collection classes in the collections module" change (bpo-25988). Aliases to ABC like collections.Mapping are kept in Python 3.9 to ease transition from Python 2.7, but will be removed in Python 3.10.

  • bpo-39104: Fix hanging ProcessPoolExcutor on shutdown(wait=False) when a task has failed pickling.

  • bpo-39627: Fixed TypedDict totality check for inherited keys.

  • bpo-39474: Fixed starting position of AST for expressions like (a)(b), (a)[b] and (a).b.

  • bpo-21016: The pydoc and trace modules now use the sysconfig module to get the path to the Python standard library, to support uncommon installation path like /usr/lib64/python3.9/ on Fedora. Patch by Jan Matějek.

  • bpo-39590: Collections.deque now holds strong references during deque.__contains__ and deque.count, fixing crashes.

  • bpo-39586: The distutils bdist_msi command is deprecated in Python 3.9, use bdist_wheel (wheel packages) instead.

  • bpo-39595: Improved performance of zipfile.Path for files with a large number of entries. Also improved performance and fixed minor issue as published with importlib_metadata 1.5.

  • bpo-39350: Fix regression in fractions.Fraction if the numerator and/or the denominator is an int subclass. The math.gcd() function is now used to normalize the numerator and denominator. math.gcd() always return a int type. Previously, the GCD type depended on numerator and denominator.

  • bpo-39567: Added audit for os.walk(), os.fwalk(), pathlib.Path.glob() and pathlib.Path.rglob().

  • bpo-39559: Remove unused, undocumented argument getters from uuid.getnode()

  • bpo-38149: sys.audit() is now called only once per call of glob.glob() and glob.iglob().

  • bpo-39546: Fix a regression in ArgumentParser where allow_abbrev=False was ignored for long options that used a prefix character other than "-".

  • bpo-39450: Striped whitespace from docstring before returning it from

  • bpo-12915: A new function resolve_name has been added to the pkgutil module. This resolves a string of the form 'a.b.c.d' or 'a.b:c.d' to an object. In the example, a.b is a package/module and c.d is an object within that package/module reached via recursive attribute access.

  • bpo-39353: The binascii.crc_hqx() function is no longer deprecated.

  • bpo-39493: Mark typing.IO.closed as a property

  • bpo-39491: Add typing.Annotated and include_extras parameter to typing.get_type_hints() as part of PEP 593. Patch by Till Varoquaux, documentation by Till Varoquaux and Konstantin Kashin.

  • bpo-39485: Fix a bug in unittest.mock.create_autospec() that would complain about the wrong number of arguments for custom descriptors defined in an extension module returning functions.

  • bpo-38932: Mock fully resets child objects on reset_mock(). Patch by Vegard Stikbakke

  • bpo-39082: Allow AsyncMock to correctly patch static/class methods

  • bpo-39432: Implement PEP-489 algorithm for non-ascii "PyInit_..." symbol names in distutils to make it export the correct init symbol also on Windows.

  • bpo-18819: Omit devmajor and devminor fields for non-device files in tarfile archives, enabling bit-for-bit compatibility with GNU tar(1).

  • bpo-39349: Added a new cancel_futures parameter to concurrent.futures.Executor.shutdown() that cancels all pending futures which have not started running, instead of waiting for them to complete before shutting down the executor.

  • bpo-39274: bool(fraction.Fraction) now returns a boolean even if (numerator != 0) does not return a boolean (ex: numpy number).

  • bpo-34793: Remove support for with (await asyncio.lock): and with (yield from asyncio.lock):. The same is correct for asyncio.Condition and asyncio.Semaphore.

  • bpo-25597: Ensure, if wraps is supplied to unittest.mock.MagicMock, it is used to calculate return values for the magic methods instead of using the default return values. Patch by Karthikeyan Singaravelan.

  • bpo-36350: inspect.Signature.parameters and inspect.BoundArguments.arguments are now dicts instead of OrderedDicts. Patch contributed by Rémi Lapeyre.

  • bpo-35727: Fix sys.exit() and sys.exit(None) exit code propagation when used in multiprocessing.Process.

  • bpo-32173: * Add lazycache function to __all__. * Use dict.clear to clear the cache. * Refactoring getline function and checkcache function.


  • bpo-17422: The language reference now specifies restrictions on class namespaces. Adapted from a patch by Ethan Furman.

  • bpo-39572: Updated documentation of total flag of TypedDict.

  • bpo-39654: In pyclbr doc, update 'class' to 'module' where appropriate and add readmodule comment. Patch by Hakan Çelik.

  • bpo-39153: Clarify refcounting semantics for the following functions: - PyObject_SetItem - PyMapping_SetItemString - PyDict_SetItem - PyDict_SetItemString

  • bpo-39392: Explain that when filling with turtle, overlap regions may be left unfilled.

  • bpo-39369: Update mmap readline method description. The fact that the readline method does update the file position should not be ignored since this might give the impression for the programmer that it doesn't update it.

  • bpo-9056: Include subsection in TOC for PDF version of docs.



  • bpo-39489: Remove COUNT_ALLOCS special build.


  • bpo-39553: Delete unused code related to SxS manifests.

  • bpo-39439: Honor the Python path when a virtualenv is active on Windows.

  • bpo-39393: Improve the error message when attempting to load a DLL with unresolved dependencies.

  • bpo-38883: home() and expanduser() on Windows now prefer USERPROFILE and no longer use HOME, which is not normally set for regular user accounts. This makes them again behave like os.path.expanduser(), which was changed to ignore HOME in 3.8, see bpo-36264.

  • bpo-39185: The build.bat script has additional options for very-quiet output (-q) and very-verbose output (-vv)


  • bpo-39663: Add tests for pyparse find_good_parse_start().

  • bpo-39600: In the font configuration window, remove duplicated font names.

  • bpo-30780: Add remaining configdialog tests for buttons and highlights and keys tabs.

  • bpo-39388: IDLE Settings Cancel button now cancels pending changes

  • bpo-38792: Close an IDLE shell calltip if a KeyboardInterrupt or shell restart occurs. Patch by Zackery Spytz.


  • bpo-35081: Move the bytes_methods.h header file to the internal C API as pycore_bytes_methods.h: it only contains private symbols (prefixed by _Py), except of the PyDoc_STRVAR_shared() macro.

  • bpo-35081: Move the dtoa.h header file to the internal C API as pycore_dtoa.h: it only contains private functions (prefixed by _Py). The math and cmath modules must now be compiled with the Py_BUILD_CORE macro defined.

  • bpo-39573: Add Py_SET_SIZE() function to set the size of an object.

  • bpo-39500: PyUnicode_IsIdentifier() does not call Py_FatalError() anymore if the string is not ready.

  • bpo-39573: Add Py_SET_TYPE() function to set the type of an object.

  • bpo-39573: Add a Py_SET_REFCNT() function to set the reference counter of an object.

  • bpo-39542: Convert PyType_HasFeature(), PyType_Check() and PyType_CheckExact() macros to static inline functions.

  • bpo-39542: In the limited C API, PyObject_INIT() and PyObject_INIT_VAR() are now defined as aliases to PyObject_Init() and PyObject_InitVar() to make their implementation opaque. It avoids to leak implementation details in the limited C API. Exclude the following functions from the limited C API: _Py_NewReference(), _Py_ForgetReference(), _PyTraceMalloc_NewReference() and _Py_GetRefTotal().

  • bpo-39542: Exclude trashcan mechanism from the limited C API: it requires access to PyTypeObject and PyThreadState structure fields, whereas these structures are opaque in the limited C API.

  • bpo-39511: The PyThreadState_Clear() function now calls the PyThreadState.on_delete callback. Previously, that happened in PyThreadState_Delete().

  • bpo-38076: Fix to clear the interpreter state only after clearing module globals to guarantee module state access from C Extensions during runtime destruction

  • bpo-39245: The Vectorcall API (PEP 590) was made public, adding the functions PyObject_Vectorcall, PyObject_VectorcallMethod, PyVectorcall_Function, PyObject_CallOneArg, PyObject_CallMethodNoArgs, PyObject_CallMethodOneArg, PyObject_FastCallDict, and the flag Py_TPFLAGS_HAVE_VECTORCALL.

Python 3.9.0 alpha 3

Release date: 2020-01-24

Core and Builtins

  • bpo-39427: Document all possibilities for the -X options in the command line help section. Patch by Pablo Galindo.

  • bpo-39421: Fix possible crashes when operating with the functions in the heapq module and custom comparison operators.

  • bpo-39386: Prevent double awaiting of async iterator.

  • bpo-17005: Add functools.TopologicalSorter to the functools module to offers functionality to perform topological sorting of graphs. Patch by Pablo Galindo, Tim Peters and Larry Hastings.

  • bpo-39320: Replace four complex bytecodes for building sequences with three simpler ones.

    The following four bytecodes have been removed:





    The following three bytecodes have been added:




  • bpo-39336: Import loaders which publish immutable module objects can now publish immutable packages in addition to individual modules.

  • bpo-39322: Added a new function gc.is_finalized() to check if an object has been finalized by the garbage collector. Patch by Pablo Galindo.

  • bpo-39048: Improve the displayed error message when incorrect types are passed to async with statements by looking up the __aenter__() special method before the __aexit__() special method when entering an asynchronous context manager. Patch by Géry Ogam.

  • bpo-39235: Fix AST end location for lone generator expression in function call, e.g. f(i for i in a).

  • bpo-39209: Correctly handle multi-line tokens in interactive mode. Patch by Pablo Galindo.

  • bpo-1635741: Port _json extension module to multiphase initialization (PEP 489).

  • bpo-39216: Fix constant folding optimization for positional only arguments - by Anthony Sottile.

  • bpo-39215: Fix SystemError when nested function has annotation on positional-only argument - by Anthony Sottile.

  • bpo-39200: Correct the error message when calling the min() or max() with no arguments. Patch by Dong-hee Na.

  • bpo-39200: Correct the error message when trying to construct range objects with no arguments. Patch by Pablo Galindo.

  • bpo-39166: Fix incorrect line execution reporting in trace functions when tracing the last iteration of asynchronous for loops. Patch by Pablo Galindo.

  • bpo-39114: Fix incorrect line execution reporting in trace functions when tracing exception handlers with name binding. Patch by Pablo Galindo.

  • bpo-39156: Split the COMPARE_OP bytecode instruction into four distinct instructions.

    • COMPARE_OP for rich comparisons

    • IS_OP for 'is' and 'is not' tests

    • CONTAINS_OP for 'in' and 'is not' tests

    • JUMP_IF_NOT_EXC_MATCH for checking exceptions in 'try-except' statements.

    This improves the clarity of the interpreter and should provide a modest speedup.

  • bpo-38588: Fix possible crashes in dict and list when calling PyObject_RichCompareBool().

  • bpo-13601: By default, sys.stderr is line-buffered now, even if stderr is redirected to a file. You can still make sys.stderr unbuffered by passing the -u command-line option or setting the PYTHONUNBUFFERED environment variable.

    (Contributed by Jendrik Seipp in bpo-13601.)

  • bpo-38610: Fix possible crashes in several list methods by holding strong references to list elements when calling PyObject_RichCompareBool().

  • bpo-32021: Include brotli .br encoding in mimetypes encodings_map


  • bpo-39430: Fixed race condition in lazy imports in tarfile.

  • bpo-39413: The os.unsetenv() function is now also available on Windows.

  • bpo-39390: Fixed a regression with the ignore callback of shutil.copytree(). The argument types are now str and List[str] again.

  • bpo-39395: The os.putenv() and os.unsetenv() functions are now always available.

  • bpo-39406: If setenv() C function is available, os.putenv() is now implemented with setenv() instead of putenv(), so Python doesn't have to handle the environment variable memory.

  • bpo-39396: Fix math.nextafter(-0.0, +0.0) on AIX 7.1.

  • bpo-29435: Allow tarfile.is_tarfile() to be used with file and file-like objects, like zipfile.is_zipfile(). Patch by William Woodruff.

  • bpo-39377: Removed encoding option from json.loads(). It has been deprecated since Python 3.1.

  • bpo-39389: Write accurate compression level metadata in gzip archives, rather than always signaling maximum compression.

  • bpo-39366: The previously deprecated xpath() and xgtitle() methods of nntplib.NNTP have been removed.

  • bpo-39357: Remove the buffering parameter of bz2.BZ2File. Since Python 3.0, it was ignored and using it was emitting DeprecationWarning. Pass an open file object, to control how the file is opened. The compresslevel parameter becomes keyword-only.

  • bpo-39353: Deprecate binhex4 and hexbin4 standards. Deprecate the binhex module and the following binascii functions: b2a_hqx(), a2b_hqx(), rlecode_hqx(), rledecode_hqx(), crc_hqx().

  • bpo-39351: Remove base64.encodestring() and base64.decodestring(), aliases deprecated since Python 3.1: use base64.encodebytes() and base64.decodebytes() instead.

  • bpo-39350: Remove fractions.gcd() function, deprecated since Python 3.5 (bpo-22486): use math.gcd() instead.

  • bpo-39329: LMTP constructor now has an optional timeout parameter. Patch by Dong-hee Na.

  • bpo-39313: Add a new exec_function option (--exec-function in the CLI) to RefactoringTool for making exec a function. Patch by Batuhan Taskaya.

  • bpo-39259: FTP_TLS and FTP_TLS now raise a ValueError if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. Patch by Dong-hee Na.

  • bpo-39259: SMTP and SMTP_SSL now raise a ValueError if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. Patch by Dong-hee Na.

  • bpo-39310: Add math.ulp(): return the value of the least significant bit of a float.

  • bpo-39297: Improved performance of importlib.metadata distribution discovery and resilients to inaccessible sys.path entries (importlib_metadata v1.4.0).

  • bpo-39259: NNTP and NNTP_SSL now raise a ValueError if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. Patch by Dong-hee Na.

  • bpo-38901: When you specify prompt='.' or equivalently python -m venv --prompt . ... the basename of the current directory is used to set the created venv's prompt when it's activated.

  • bpo-39288: Add math.nextafter(): return the next floating-point value after x towards y.

  • bpo-39259: POP3 and POP3_SSL now raise a ValueError if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. Patch by Dong-hee Na.

  • bpo-39242: Updated the Gmane domain from to which is used for examples of NNTP news reader server and nntplib tests.

  • bpo-35292: Proxy the SimpleHTTPRequestHandler.guess_type to mimetypes.guess_type so the mimetypes.init is called lazily to avoid unnecessary costs when http.server module is imported.

  • bpo-39239: The select.epoll.unregister() method no longer ignores the EBADF error.

  • bpo-38907: In http.server script, restore binding to IPv4 on Windows.

  • bpo-39152: Fix ttk.Scale.configure([name]) to return configuration tuple for name or all options. Giovanni Lombardo contributed part of the patch.

  • bpo-39198: If an exception were to be thrown in Logger.isEnabledFor (say, by asyncio timeouts or stopit) , the logging global lock may not be released appropriately, resulting in deadlock. This change wraps that block of code with try...finally to ensure the lock is released.

  • bpo-39191: Perform a check for running loop before starting a new task in loop.run_until_complete() to fail fast; it prevents the side effect of new task spawning before exception raising.

  • bpo-38871: Correctly parenthesize filter-based statements that contain lambda expressions in mod:lib2to3. Patch by Dong-hee Na.

  • bpo-39142: A change was made to logging.config.dictConfig to avoid converting instances of named tuples to ConvertingTuple. It's assumed that named tuples are too specialised to be treated like ordinary tuples; if a user of named tuples requires ConvertingTuple functionality, they will have to implement that themselves in their named tuple class.

  • bpo-39158: ast.literal_eval() now supports empty sets.

  • bpo-39129: Fix import path for asyncio.TimeoutError

  • bpo-39057: urllib.request.proxy_bypass_environment() now ignores leading dots and no longer ignores a trailing newline.

  • bpo-39056: Fixed handling invalid warning category in the -W option. No longer import the re module if it is not needed.

  • bpo-39055: base64.b64decode() with validate=True raises now a binascii.Error if the input ends with a single \n.

  • bpo-21600: Fix mock.patch.stopall() to stop active patches that were created with mock.patch.dict().

  • bpo-39019: Implement dummy __class_getitem__ for tempfile.SpooledTemporaryFile.

  • bpo-39019: Implement dummy __class_getitem__ for subprocess.Popen, subprocess.CompletedProcess

  • bpo-38914: Adjusted the wording of the warning issued by distutils' check command when the author and maintainer fields are supplied but no corresponding e-mail field (author_email or maintainer_email) is found. The wording now reflects the fact that these fields are suggested, but not required. Patch by Juergen Gmach.

  • bpo-38878: Fixed __subclasshook__ of os.PathLike to return a correct result upon inheritance. Patch by Bar Harel.

  • bpo-38615: IMAP4 and IMAP4_SSL now have an optional timeout parameter for their constructors. Also, the open() method now has an optional timeout parameter with this change. The overridden methods of IMAP4_SSL and IMAP4_stream were applied to this change. Patch by Dong-hee Na.

  • bpo-35182: Fixed Popen.communicate() subsequent call crash when the child process has already closed any piped standard stream, but still continues to be running. Patch by Andriy Maletsky.

  • bpo-38630: On Unix, subprocess.Popen.send_signal() now polls the process status. Polling reduces the risk of sending a signal to the wrong process if the process completed, the subprocess.Popen.returncode attribute is still None, and the pid has been reassigned (recycled) to a new different process.

  • bpo-38536: Removes trailing space in formatted currency with international=True and a locale with symbol following value. E.g. locale.currency(12.34, international=True) returned '12,34 EUR ' instead of '12,34 EUR'.

  • bpo-38473: Use signature from inner mock for autospecced methods attached with unittest.mock.attach_mock(). Patch by Karthikeyan Singaravelan.

  • bpo-38361: Fixed an issue where ident could include a leading path separator when syslog.openlog() was called without arguments.

  • bpo-38293: Add copy.copy() and copy.deepcopy() support to property() objects.

  • bpo-37958: Added the pstats.Stats.get_profile_dict() method to return the profile data as a StatsProfile instance.

  • bpo-28367: Termios magic constants for the following baud rates: - B500000 - B576000 - B921600 - B1000000 - B1152000 - B1500000 - B2000000 - B2500000 - B3000000 - B3500000 - B4000000 Patch by Andrey Smirnov



  • bpo-39395: On non-Windows platforms, the setenv() and unsetenv() functions are now required to build Python.

  • bpo-39160: Updated the documentation in /configure --help to show default values, reference documentation where required and add additional explanation where needed.

  • bpo-39144: The ctags and etags build targets both include Modules/_ctypes and Python standard library source files.


  • bpo-39050: Make IDLE Settings dialog Help button work again.

  • bpo-34118: Tag memoryview, range, and tuple as classes, the same as list, etcetera, in the library manual built-in functions list.

  • bpo-32989: Add tests for editor newline_and_indent_event method. Remove dead code from pyparse find_good_parse_start method.


  • bpo-39372: Clean header files of interfaces defined but with no implementation. The public API symbols being removed are: _PyBytes_InsertThousandsGroupingLocale, _PyBytes_InsertThousandsGrouping, _Py_InitializeFromArgs, _Py_InitializeFromWideArgs, _PyFloat_Repr, _PyFloat_Digits, _PyFloat_DigitsInit, PyFrame_ExtendStack, _PyAIterWrapper_Type, PyNullImporter_Type, PyCmpWrapper_Type, PySortWrapper_Type, PyNoArgsFunction.

  • bpo-39164: Add a private _PyErr_GetExcInfo() function to retrieve exception information of the specified Python thread state.

Python 3.9.0 alpha 2

Release date: 2019-12-18


  • bpo-38945: Newline characters have been escaped when performing uu encoding to prevent them from overflowing into to content section of the encoded file. This prevents malicious or accidental modification of data during the decoding process.

  • bpo-37228: Due to significant security concerns, the reuse_address parameter of asyncio.loop.create_datagram_endpoint() is no longer supported. This is because of the behavior of SO_REUSEADDR in UDP. For more details, see the documentation for loop.create_datagram_endpoint(). (Contributed by Kyle Stanley, Antoine Pitrou, and Yury Selivanov in bpo-37228.)

  • bpo-38804: Fixes a ReDoS vulnerability in http.cookiejar. Patch by Ben Caller.

Core and Builtins

  • bpo-39028: Slightly improve the speed of keyword argument parsing with many kwargs by strengthening the assumption that kwargs are interned strings.

  • bpo-39080: Fix the value of end_col_offset for Starred Expression AST nodes when they are among the elements in the args attribute of Call AST nodes.

  • bpo-39031: When parsing an "elif" node, lineno and col_offset of the node now point to the "elif" keyword and not to its condition, making it consistent with the "if" node. Patch by Lysandros Nikolaou.

  • bpo-20443: In Python 3.9.0a1, sys.argv[0] was made an absolute path if a filename was specified on the command line. Revert this change, since most users expect sys.argv to be unmodified.

  • bpo-39008: PySys_Audit() now requires Py_ssize_t to be used for size arguments in the format string, regardless of whether PY_SSIZE_T_CLEAN was defined at include time.

  • bpo-38673: In REPL mode, don't switch to PS2 if the line starts with comment or whitespace. Based on work by Batuhan Taşkaya.

  • bpo-38922: Calling replace on a code object now raises the code.__new__ audit event.

  • bpo-38920: Add audit hooks for when sys.excepthook() and sys.unraisablehook() are invoked.

  • bpo-38892: Improve documentation for audit events table and functions.

  • bpo-38852: Set the thread stack size to 8 Mb for debug builds on android platforms.

  • bpo-38858: Each Python subinterpreter now has its own "small integer singletons": numbers in [-5; 257] range. It is no longer possible to change the number of small integers at build time by overriding NSMALLNEGINTS and NSMALLPOSINTS macros: macros should now be modified manually in pycore_pystate.h header file.

  • bpo-36854: The garbage collector state becomes per interpreter (PyInterpreterState.gc), rather than being global (_PyRuntimeState.gc).

  • bpo-38835: The PyFPE_START_PROTECT() and PyFPE_END_PROTECT() macros are empty: they have been doing nothing for the last year, so stop using them.

  • bpo-38328: Sped up the creation time of constant list and set displays. Patch by Brandt Bucher.

  • bpo-38707: MainThread.native_id is now correctly reset in child processes spawned using multiprocessing.Process, instead of retaining the parent's value.

  • bpo-38629: Added __floor__ and __ceil__ methods to float object. Patch by Batuhan Taşkaya.

  • bpo-27145: int + int and int - int operators can now return small integer singletons. Patch by hongweipeng.

  • bpo-38021: Provide a platform tag for AIX that is sufficient for PEP425 binary distribution identification. Patch by Michael Felt.

  • bpo-35409: Ignore GeneratorExit exceptions when throwing an exception into the aclose coroutine of an asynchronous generator.

  • bpo-33387: Removed WITH_CLEANUP_START, WITH_CLEANUP_FINISH, BEGIN_FINALLY, END_FINALLY, CALL_FINALLY and POP_FINALLY bytecodes. Replaced with RERAISE and WITH_EXCEPT_START bytecodes. The compiler now generates different code for exceptional and non-exceptional branches for 'with' and 'try-except' statements. For 'try-finally' statements the 'finally' block is replicated for each exit from the 'try' body.


  • bpo-39033: Fix NameError in zipimport. Patch by Karthikeyan Singaravelan.

  • bpo-39022: Update importlib.metadata to include improvements from importlib_metadata 1.3 including better serialization of EntryPoints and improved documentation for custom finders.

  • bpo-39006: Fix asyncio when the ssl module is missing: only check for ssl.SSLSocket instance if the ssl module is available.

  • bpo-38708: Fix a potential IndexError in email parser when parsing an empty msg-id.

  • bpo-38698: Add a new InvalidMessageID token to email parser to represent invalid Message-ID headers. Also, add defects when there is remaining value after parsing the header.

  • bpo-38994: Implement __class_getitem__ for os.PathLike, pathlib.Path.

  • bpo-38979: Return class from ContextVar.__class_getitem__ to simplify subclassing.

  • bpo-38978: Implement __class_getitem__ on asyncio objects (Future, Task, Queue). Patch by Batuhan Taskaya.

  • bpo-38916: array.array: Remove tostring() and fromstring() methods. They were aliases to tobytes() and frombytes(), deprecated since Python 3.2.

  • bpo-38986: Make repr of C accelerated TaskWakeupMethWrapper the same as of pure Python version.

  • bpo-38982: Fix asyncio PidfdChildWatcher: handle waitpid() error. If waitpid() is called elsewhere, waitpid() call fails with ChildProcessError: use return code 255 in this case, and log a warning. It ensures that the pidfd file descriptor is closed if this error occurs.

  • bpo-38529: Drop too noisy asyncio warning about deletion of a stream without explicit .close() call.

  • bpo-27413: Added ability to pass through ensure_ascii options to json.dumps in the json.tool command-line interface.

  • bpo-38634: The readline module now detects if Python is linked to libedit at runtime on all platforms. Previously, the check was only done on macOS.

  • bpo-33684: Fix json.tool failed to read a JSON file with non-ASCII characters when locale encoding is not UTF-8.

  • bpo-38698: Prevent UnboundLocalError to pop up in parse_message_id.

    parse_message_id() was improperly using a token defined inside an exception handler, which was raising UnboundLocalError on parsing an invalid value. Patch by Claudiu Popa.

  • bpo-38927: Use python -m pip instead of pip to upgrade dependencies in venv.

  • bpo-26730: Fix SpooledTemporaryFile.rollover() might corrupt the file when it is in text mode. Patch by Serhiy Storchaka.

  • bpo-38881: random.choices() now raises a ValueError when all the weights are zero.

  • bpo-38876: Raise pickle.UnpicklingError when loading an item from memo for invalid input.

    The previous code was raising a KeyError for both the Python and C implementation. This was caused by the specified index of an invalid input which did not exist in the memo structure, where the pickle stores what objects it has seen. The malformed input would have caused either a BINGET or LONG_BINGET load from the memo, leading to a KeyError as the determined index was bogus. Patch by Claudiu Popa

  • bpo-38688: Calling func:shutil.copytree to copy a directory tree from one directory to another subdirectory resulted in an endless loop and a RecursionError. A fix was added to consume an iterator and create the list of the entries to be copied, avoiding the recursion for newly created directories. Patch by Bruno P. Kinoshita.

  • bpo-38863: Improve is_cgi() function in http.server, which enables processing the case that cgi directory is a child of another directory other than root.

  • bpo-37838: typing.get_type_hints() properly handles functions decorated with functools.wraps().

  • bpo-38870: Expose ast.unparse() as a function of the ast module that can be used to unparse an ast.AST object and produce a string with code that would produce an equivalent ast.AST object when parsed. Patch by Pablo Galindo and Batuhan Taskaya.

  • bpo-38859: AsyncMock now returns StopAsyncIteration on the exhaustion of a side_effects iterable. Since PEP-479 its Impossible to raise a StopIteration exception from a coroutine.

  • bpo-38857: AsyncMock fix for return values that are awaitable types. This also covers side_effect iterable values that happened to be awaitable, and wraps callables that return an awaitable type. Before these awaitables were being awaited instead of being returned as is.

  • bpo-38834: typing.TypedDict subclasses now track which keys are optional using the __required_keys__ and __optional_keys__ attributes, to enable runtime validation by downstream projects. Patch by Zac Hatfield-Dodds.

  • bpo-38821: Fix unhandled exceptions in argparse when internationalizing error messages for arguments with nargs set to special (non-integer) values. Patch by Federico Bond.

  • bpo-38820: Make Python compatible with OpenSSL 3.0.0. ssl.SSLSocket.getpeercert() no longer returns IPv6 addresses with a trailing new line.

  • bpo-38811: Fix an unhandled exception in pathlib when is missing. Patch by Toke Høiland-Jørgensen.

  • bpo-38686: Added support for multiple qop values in urllib.request.AbstractDigestAuthHandler.

  • bpo-38712: Add the Linux-specific signal.pidfd_send_signal() function, which allows sending a signal to a process identified by a file descriptor rather than a pid.

  • bpo-38348: Add -i and --indent (indentation level), and --no-type-comments (type comments) command line options to ast parsing tool.

  • bpo-37523: Change zipfile.ZipExtFile to raise ValueError when trying to access the underlying file object after it has been closed. This new behavior is consistent with how accessing closed files is handled in other parts of Python.

  • bpo-38045: Improve the performance of enum._decompose() in enum. Patch by hongweipeng.

  • bpo-36820: Break cycle generated when saving an exception in, and as they keep alive not only the exception but user objects through the __traceback__ attribute. Patch by Mario Corchero.

  • bpo-36406: Handle namespace packages in doctest. Patch by Karthikeyan Singaravelan.

  • bpo-34776: Fix dataclasses to support forward references in type annotations

  • bpo-20928: ElementTree supports recursive XInclude processing. Patch by Stefan Behnel.

  • bpo-29636: Add whitespace options for formatting JSON with the json.tool CLI. The following mutually exclusive options are now supported: --indent for setting the indent level in spaces; --tab for indenting with tabs; --no-indent for suppressing newlines; and --compact for suppressing all whitespace. The default behavior remains the same as --indent=4.



  • bpo-38546: Fix test_ressources_gced_in_workers() of test_concurrent_futures: explicitly stop the manager to prevent leaking a child process running in the background after the test completes.

  • bpo-38546: Multiprocessing and concurrent.futures tests now stop the resource tracker process when tests complete.

  • bpo-38614: Replace hardcoded timeout constants in tests with new constants: LOOPBACK_TIMEOUT, INTERNET_TIMEOUT, SHORT_TIMEOUT and LONG_TIMEOUT. It becomes easier to adjust these four timeout constants for all tests at once, rather than having to adjust every single test file.

  • bpo-38547: Fix test_pty: if the process is the session leader, closing the master file descriptor raises a SIGHUP signal: simply ignore SIGHUP when running the tests.

  • bpo-38992: Fix a test for math.fsum() that was failing due to constant folding.

  • bpo-38991: run_python_until_end(), assert_python_ok() and assert_python_failure() functions no longer strip whitespaces from stderr. Remove function.

  • bpo-38965: Fix test_faulthandler on GCC 10. Use the "volatile" keyword in faulthandler._stack_overflow() to prevent tail call optimization on any compiler, rather than relying on compiler specific pragma.

  • bpo-38875: test_capi: trashcan tests now require the test "cpu" resource.

  • bpo-38841: Skip asyncio test_create_datagram_endpoint_existing_sock_unix on platforms lacking a functional bind() for named unix domain sockets.

  • bpo-38692: Skip the test_posix.test_pidfd_open() test if os.pidfd_open() fails with a PermissionError. This situation can happen in a Linux sandbox using a syscall whitelist which doesn't allow the pidfd_open() syscall yet.

  • bpo-38839: Fix some unused functions in tests. Patch by Adam Johnson.

  • bpo-38669: Raise TypeError when passing target as a string with unittest.mock.patch.object().

  • bpo-37957: test.regrtest now can receive a list of test patterns to ignore (using the -i/--ignore argument) or a file with a list of patterns to ignore (using the --ignore-file argument). Patch by Pablo Galindo.


  • bpo-37404: asyncio now raises TyperError when calling incompatible methods with an ssl.SSLSocket socket. Patch by Ido Michael.

  • bpo-36500: Added an optional "regen" project to the Visual Studio solution that will regenerate all grammar, tokens, and opcodes.


  • bpo-39007: Add auditing events to functions in winreg.

  • bpo-33125: Add support for building and releasing Windows ARM64 packages.


  • bpo-37931: Fixed a crash on OSX dynamic builds that occurred when re-initializing the posix module after a Py_Finalize if the environment had changed since the previous import posix. Patch by Benoît Hudson.


  • bpo-38944: Escape key now closes IDLE completion windows. Patch by Johnny Najera.

  • bpo-38943: Fix IDLE autocomplete windows not always appearing on some systems. Patch by Johnny Najera.

  • bpo-38862: 'Strip Trailing Whitespace' on the Format menu removes extra newlines at the end of non-shell files.

  • bpo-38636: Fix IDLE Format menu tab toggle and file indent width. These functions (default shortcuts Alt-T and Alt-U) were mistakenly disabled in 3.7.5 and 3.8.0.


  • bpo-38896: Remove PyUnicode_ClearFreeList() function: the Unicode free list has been removed in Python 3.3.

  • bpo-37340: Remove PyMethod_ClearFreeList() and PyCFunction_ClearFreeList() functions: the free lists of bound method objects have been removed.

  • bpo-38835: Exclude PyFPE_START_PROTECT() and PyFPE_END_PROTECT() macros of pyfpe.h from Py_LIMITED_API (stable API).

Python 3.9.0 alpha 1

Release date: 2019-11-19


Core and Builtins

  • bpo-38631: Replace Py_FatalError() call with a regular RuntimeError exception in float.__getformat__().

  • bpo-38639: Optimized math.floor(), math.ceil() and math.trunc() for floats.

  • bpo-38640: Fixed a bug in the compiler that was causing to raise in the presence of break statements and continue statements inside always false while loops. Patch by Pablo Galindo.

  • bpo-38613: Optimized some set operations (e.g. |, ^, and -) of dict_keys. d.keys() | other was slower than set(d) | other but they are almost same performance for now.

  • bpo-28029: "".replace("", s, n) now returns s instead of an empty string for all non-zero n. There are similar changes for bytes and bytearray objects.

  • bpo-38535: Fixed line numbers and column offsets for AST nodes for calls without arguments in decorators.

  • bpo-38525: Fix a segmentation fault when using reverse iterators of empty dict objects. Patch by Dong-hee Na and Inada Naoki.

  • bpo-38465: bytearray, array and mmap objects allow now to export more than 2**31 buffers at a time.

  • bpo-38469: Fixed a bug where the scope of named expressions was not being resolved correctly in the presence of the global keyword. Patch by Pablo Galindo.

  • bpo-38437: Activate the GC_DEBUG macro for debug builds of the interpreter (when Py_DEBUG is set). Patch by Pablo Galindo.

  • bpo-38379: When the garbage collector makes a collection in which some objects resurrect (they are reachable from outside the isolated cycles after the finalizers have been executed), do not block the collection of all objects that are still unreachable. Patch by Pablo Galindo and Tim Peters.

  • bpo-38379: When cyclic garbage collection (gc) runs finalizers that resurrect unreachable objects, the current gc run ends, without collecting any cyclic trash. However, the statistics reported by collect() and get_stats() claimed that all cyclic trash found was collected, and that the resurrected objects were collected. Changed the stats to report that none were collected.

  • bpo-38392: In debug mode, PyObject_GC_Track() now calls tp_traverse() of the object type to ensure that the object is valid: test that objects visited by tp_traverse() are valid.

  • bpo-38210: Remove unnecessary intersection and update set operation in dictview with empty set. (Contributed by Dong-hee Na in bpo-38210.)

  • bpo-38402: Check the error from the system's underlying crypt or crypt_r.

  • bpo-37474: On FreeBSD, Python no longer calls fedisableexcept() at startup to control the floating point control mode. The call became useless since FreeBSD 6: it became the default mode.

  • bpo-38006: Fix a bug due to the interaction of weakrefs and the cyclic garbage collector. We must clear any weakrefs in garbage in order to prevent their callbacks from executing and causing a crash.

  • bpo-38317: Fix warnings options priority: PyConfig.warnoptions has the highest priority, as stated in the PEP 587.

  • bpo-38310: Predict BUILD_MAP_UNPACK_WITH_CALL -> CALL_FUNCTION_EX opcode pairs in the main interpreter loop. Patch by Brandt Bucher.

  • bpo-36871: Improve error handling for the assert_has_calls and assert_has_awaits methods of mocks. Fixed a bug where any errors encountered while binding the expected calls to the mock's spec were silently swallowed, leading to misleading error output.

  • bpo-11410: Better control over symbol visibility is provided through use of the visibility attributes available in gcc >= 4.0, provided in a uniform way across POSIX and Windows. The POSIX build files have been updated to compile with -fvisibility=hidden, minimising exported symbols.

  • bpo-38219: Optimized the dict constructor and the update() method for the case when the argument is a dict.

  • bpo-38236: Python now dumps path configuration if it fails to import the Python codecs of the filesystem and stdio encodings.

  • bpo-38013: Allow to call async_generator_athrow().throw(...) even for non-started async generator helper. It fixes annoying warning at the end of call.

  • bpo-38124: Fix an off-by-one error in PyState_AddModule that could cause out-of-bounds memory access.

  • bpo-38116: The select module is now PEP-384 compliant and no longer has static state

  • bpo-38113: ast module updated to PEP-384 and all statics removed

  • bpo-38076: The struct module is now PEP-384 compatible

  • bpo-38075: The random module is now PEP-384 compatible

  • bpo-38074: zlib module made PEP-384 compatible

  • bpo-38073: Make pwd extension module PEP-384 compatible

  • bpo-38072: grp module made PEP-384 compatible

  • bpo-38069: Make _posixsubprocess PEP-384 compatible

  • bpo-38071: Make termios extension module PEP-384 compatible

  • bpo-38005: Fixed comparing and creating of InterpreterID and ChannelID.

  • bpo-36946: Fix possible signed integer overflow when handling slices. Patch by hongweipeng.

  • bpo-37994: Fixed silencing arbitrary errors if an attribute lookup fails in several sites. Only AttributeError should be silenced.

  • bpo-8425: Optimize set difference_update for the case when the other set is much larger than the base set. (Suggested by Evgeny Kapun with code contributed by Michele Orrù).

  • bpo-37966: The implementation of is_normalized() has been greatly sped up on strings that aren't normalized, by implementing the full normalization-quick-check algorithm from the Unicode standard.

  • bpo-37947: Adjust correctly the recursion level in the symtable generation for named expressions. Patch by Pablo Galindo.

  • bpo-37812: The CHECK_SMALL_INT macro used inside Object/longobject.c has been replaced with an explicit return at each call site.

  • bpo-37751: Fix codecs.lookup() to normalize the encoding name the same way than encodings.normalize_encoding(), except that codecs.lookup() also converts the name to lower case.

  • bpo-37830: Fixed compilation of break and continue in the finally block when the corresponding try block contains return with a non-constant value.

  • bpo-20490: Improve import error message for partially initialized module on circular from imports - by Anthony Sottile.

  • bpo-37840: Fix handling of negative indices in sq_item of bytearray. Patch by Sergey Fedoseev.

  • bpo-37802: Slightly improve performance of PyLong_FromUnsignedLong(), PyLong_FromUnsignedLongLong() and PyLong_FromSize_t(). Patch by Sergey Fedoseev.

  • bpo-37409: Ensure explicit relative imports from interactive sessions and scripts (having no parent package) always raise ImportError, rather than treating the current module as the package. Patch by Ben Lewis.

  • bpo-32912: Reverted bpo-32912: emitting SyntaxWarning instead of DeprecationWarning for invalid escape sequences in string and bytes literals.

  • bpo-37757: PEP 572: As described in the PEP, assignment expressions now raise SyntaxError when their interaction with comprehension scoping results in an ambiguous target scope.

    The TargetScopeError subclass originally proposed by the PEP has been removed in favour of just raising regular syntax errors for the disallowed cases.

  • bpo-36279: Fix potential use of uninitialized memory in os.wait3().

  • bpo-36311: Decoding bytes objects larger than 2GiB is faster and no longer fails when a multibyte characters spans a chunk boundary.

  • bpo-34880: The assert statement now works properly if the AssertionError exception is being shadowed. Patch by Zackery Spytz.

  • bpo-37340: Removed object cache (free_list) for bound method objects. Temporary bound method objects are less used than before thanks to the LOAD_METHOD opcode and the _PyObject_VectorcallMethod C API.

  • bpo-37648: Fixed minor inconsistency in list.__contains__(), tuple.__contains__() and a few other places. The collection's item is now always at the left and the needle is on the right of ==.

  • bpo-37444: Update differing exception between builtins.__import__() and importlib.__import__().

  • bpo-37619: When adding a wrapper descriptor from one class to a different class (for example, setting __add__ = str.__add__ on an int subclass), an exception is correctly raised when the operator is called.

  • bpo-37593: Swap the positions of the posonlyargs and args parameters in the constructor of ast.parameters nodes.

  • bpo-37543: Optimized pymalloc for non PGO build.

  • bpo-37537: Compute allocated pymalloc blocks inside _Py_GetAllocatedBlocks(). This slows down _Py_GetAllocatedBlocks() but gives a small speedup to _PyObject_Malloc() and _PyObject_Free().

  • bpo-37467: Fix sys.excepthook() and PyErr_Display() if a filename is a bytes string. For example, for a SyntaxError exception where the filename attribute is a bytes string.

  • bpo-37433: Fix SyntaxError indicator printing too many spaces for multi-line strings - by Anthony Sottile.

  • bpo-37417: bytearray.extend() now correctly handles errors that arise during iteration. Patch by Brandt Bucher.

  • bpo-37414: The undocumented sys.callstats() function has been removed. Since Python 3.7, it was deprecated and always returned None. It required a special build option CALL_PROFILE which was already removed in Python 3.7.

  • bpo-37392: Remove sys.getcheckinterval() and sys.setcheckinterval() functions. They were deprecated since Python 3.2. Use sys.getswitchinterval() and sys.setswitchinterval() instead. Remove also check_interval field of the PyInterpreterState structure.

  • bpo-37388: In development mode and in debug build, encoding and errors arguments are now checked on string encoding and decoding operations. Examples: open(), str.encode() and bytes.decode().

    By default, for best performances, the errors argument is only checked at the first encoding/decoding error, and the encoding argument is sometimes ignored for empty strings.

  • bpo-37348: Optimized decoding short ASCII string with UTF-8 and ascii codecs. b"foo".decode() is about 15% faster. Patch by Inada Naoki.

  • bpo-24214: Improved support of the surrogatepass error handler in the UTF-8 and UTF-16 incremental decoders.

  • bpo-37330: open(),, and fileinput.FileInput no longer accept 'U' ("universal newline") in the file mode. This flag was deprecated since Python 3.3.

  • bpo-35224: Reverse evaluation order of key: value in dict comprehensions as proposed in PEP 572. I.e. in {k: v for ...}, k will be evaluated before v.

  • bpo-37316: Fix the PySys_Audit() call in mmap.mmap.

  • bpo-37300: Remove an unnecessary Py_XINCREF in classobject.c.

  • bpo-37269: Fix a bug in the peephole optimizer that was not treating correctly constant conditions with binary operators. Patch by Pablo Galindo.

  • bpo-20443: Python now gets the absolute path of the script filename specified on the command line (ex: "python3"): the __file__ attribute of the __main__ module and sys.path[0] become an absolute path, rather than a relative path.

  • bpo-37257: Python's small object allocator (obmalloc.c) now allows (no more than) one empty arena to remain available for immediate reuse, without returning it to the OS. This prevents thrashing in simple loops where an arena could be created and destroyed anew on each iteration.

  • bpo-37231: The dispatching of type slots to special methods (for example calling __mul__ when doing x * y) has been made faster.

  • bpo-36974: Implemented separate vectorcall functions for every calling convention of builtin functions and methods. This improves performance for calls.

  • bpo-37213: Handle correctly negative line offsets in the peephole optimizer. Patch by Pablo Galindo.

  • bpo-37219: Remove erroneous optimization for empty set differences.

  • bpo-15913: Implement PyBuffer_SizeFromFormat() function (previously documented but not implemented): call struct.calcsize(). Patch by Joannah Nanjekye.

  • bpo-36922: Slot functions optimize any callable with Py_TPFLAGS_METHOD_DESCRIPTOR instead of only instances of function.

  • bpo-36974: The slot tp_vectorcall_offset is inherited unconditionally to support super().__call__() when the base class uses vectorcall.

  • bpo-37160: threading.get_native_id() now also supports NetBSD.

  • bpo-37077: Add threading.get_native_id() support for AIX. Patch by M. Felt

  • bpo-36781: sum() has been optimized for boolean values.

  • bpo-34556: Add --upgrade-deps to venv module. Patch by Cooper Ry Lees

  • bpo-20523: pdb.Pdb supports ~/.pdbrc in Windows 7. Patch by Tim Hopper and Dan Lidral-Porter.

  • bpo-35551: Updated encodings: - Removed the "tis260" encoding, which was an alias for the nonexistent "tactis" codec. - Added "mac_centeuro" as an alias for the mac_latin2 encoding.

  • bpo-19072: The classmethod decorator can now wrap other descriptors such as property objects. Adapted from a patch written by Graham Dumpleton.

  • bpo-27575: Improve speed of dictview intersection by directly using set intersection logic. Patch by David Su.

  • bpo-30773: Prohibit parallel running of aclose() / asend() / athrow(). Fix ag_running to reflect the actual running status of the AG.


  • bpo-36589: The curses.update_lines_cols() function now returns None instead of 1 on success.

  • bpo-38807: Update TypeError messages for os.path.join() to include os.PathLike objects as acceptable input types.

  • bpo-38724: Add a repr for subprocess.Popen objects. Patch by Andrey Doroschenko.

  • bpo-38786: pydoc now recognizes and parses HTTPS URLs. Patch by python273.

  • bpo-38785: Prevent asyncio from crashing if parent __init__ is not called from a constructor of object derived from asyncio.Future.

  • bpo-38723: pdb now uses io.open_code() to trigger auditing events.

  • bpo-27805: Allow opening pipes and other non-seekable files in append mode with open().

  • bpo-38438: Simplify the argparse usage message for nargs="*".

  • bpo-38761: WeakSet is now registered as a

  • bpo-38716: logging: change RotatingHandler namer and rotator to class-level attributes. This stops __init__ from setting them to None in the case where a subclass defines them with eponymous methods.

  • bpo-38713: Add os.P_PIDFD constant, which may be passed to os.waitid() to wait on a Linux process file descriptor.

  • bpo-38692: Add asyncio.PidfdChildWatcher, a Linux-specific child watcher implementation that polls process file descriptors.

  • bpo-38692: Expose the Linux pidfd_open syscall as os.pidfd_open().

  • bpo-38602: Added constants F_OFD_GETLK, F_OFD_SETLK and F_OFD_SETLKW to the fcntl module. Patch by Dong-hee Na.

  • bpo-38334: Fixed seeking backward on an encrypted zipfile.ZipExtFile.

  • bpo-38312: Add curses.get_escdelay(), curses.set_escdelay(), curses.get_tabsize(), and curses.set_tabsize() functions - by Anthony Sottile.

  • bpo-38586: Now fileConfig() correctly sets the .name of handlers loaded.

  • bpo-38565: Add new cache_parameters() method for functools.lru_cache() to better support pickling.

  • bpo-34679: asynci.ProactorEventLoop.close() now only calls signal.set_wakeup_fd() in the main thread.

  • bpo-31202: The case the result of pathlib.WindowsPath.glob() matches now the case of the pattern for literal parts.

  • bpo-36321: Remove misspelled attribute. The 3.8 changelog noted that this would be removed in 3.9.

  • bpo-38521: Fixed erroneous equality comparison in statistics.NormalDist().

  • bpo-38493: Added CLD_KILLED and CLD_STOPPED for si_code. Patch by Dong-hee Na.

  • bpo-38478: Fixed a bug in inspect.signature.bind() that was causing it to fail when handling a keyword argument with same name as positional-only parameter. Patch by Pablo Galindo.

  • bpo-33604: Fixed and hmac.HMAC to raise TypeError instead of ValueError when the digestmod parameter, now required in 3.8, is omitted. Also clarified the hmac module documentation and docstrings.

  • bpo-38378: Parameters out and in of os.sendfile() was renamed to out_fd and in_fd.

  • bpo-38417: Added support for setting the umask in the child process to the subprocess module on POSIX systems.

  • bpo-38449: Revert GH-15522, which introduces a regression in mimetypes.guess_type() due to improper handling of filenames as urls.

  • bpo-38431: Fix __repr__ method for dataclasses.InitVar to support typing objects, patch by Samuel Colvin.

  • bpo-38109: Add missing stat.S_IFDOOR, stat.S_IFPORT, stat.S_IFWHT, stat.S_ISDOOR(), stat.S_ISPORT(), and stat.S_ISWHT() values to the Python implementation of stat.

  • bpo-38422: Clarify docstrings of pathlib suffix(es)

  • bpo-38405: Nested subclasses of typing.NamedTuple are now pickleable.

  • bpo-38332: Prevent KeyError thrown by _encoded_words.decode() when given an encoded-word with invalid content-type encoding from propagating all the way to email.message.get().

  • bpo-38371: Deprecated the split() method in _tkinter.TkappType in favour of the splitlist() method which has more consistent and predicable behavior.

  • bpo-38341: Add smtplib.SMTPNotSupportedError to the smtplib exported names.

  • bpo-38319: sendfile() used in socket and shutil modules was raising OverflowError for files >= 2GiB on 32-bit architectures. (patch by Giampaolo Rodola)

  • bpo-38242: Revert the new asyncio Streams API

  • bpo-13153: OS native encoding is now used for converting between Python strings and Tcl objects. This allows to display, copy and paste to clipboard emoji and other non-BMP characters. Converting strings from Tcl to Python and back now never fails (except MemoryError).

  • bpo-38019: Correctly handle pause/resume reading of closed asyncio unix pipe.

  • bpo-38163: Child mocks will now detect their type as either synchronous or asynchronous, asynchronous child mocks will be AsyncMocks and synchronous child mocks will be either MagicMock or Mock (depending on their parent type).

  • bpo-38161: Removes _AwaitEvent from AsyncMock.

  • bpo-38216: Allow the rare code that wants to send invalid http requests from the http.client library a way to do so. The fixes for bpo-30458 led to breakage for some projects that were relying on this ability to test their own behavior in the face of bad requests.

  • bpo-28286: Deprecate opening GzipFile for writing implicitly. Always specify the mode argument for writing.

  • bpo-38108: Any synchronous magic methods on an AsyncMock now return a MagicMock. Any asynchronous magic methods on a MagicMock now return an AsyncMock.

  • bpo-38265: Update the length parameter of os.pread() to accept Py_ssize_t instead of int.

  • bpo-38112: compileall has a higher default recursion limit and new command-line arguments for path manipulation, symlinks handling, and multiple optimization levels.

  • bpo-38248: asyncio: Fix inconsistent immediate Task cancellation

  • bpo-38237: The arguments for the builtin pow function are more descriptive. They can now also be passed in as keywords.

  • bpo-34002: Improve efficiency in parts of email package by changing while-pop to a for loop, using isdisjoint instead of set intersections.

  • bpo-38191: Constructors of NamedTuple and TypedDict types now accept arbitrary keyword argument names, including "cls", "self", "typename", "_typename", "fields" and "_fields".

  • bpo-38155: Add __all__ to datetime. Patch by Tahia Khan.

  • bpo-38185: Fixed case-insensitive string comparison in sqlite3.Row indexing.

  • bpo-38136: Changes AsyncMock call count and await count to be two different counters. Now await count only counts when a coroutine has been awaited, not when it has been called, and vice-versa. Update the documentation around this.

  • bpo-37828: Fix default mock name in unittest.mock.Mock.assert_called() exceptions. Patch by Abraham Toriz Cruz.

  • bpo-38175: Fix a memory leak in comparison of sqlite3.Row objects.

  • bpo-33936: _hashlib no longer calls obsolete OpenSSL initialization function with OpenSSL 1.1.0+.

  • bpo-34706: Preserve subclassing in inspect.Signature.from_callable.

  • bpo-38153: Names of hashing algorithms from OpenSSL are now normalized to follow Python's naming conventions. For example OpenSSL uses sha3-512 instead of sha3_512 or blake2b512 instead of blake2b.

  • bpo-38115: Fix a bug in dis.findlinestarts() where it would return invalid bytecode offsets. Document that a code object's co_lnotab can contain invalid bytecode offsets.

  • bpo-38148: Add slots to asyncio transport classes, which can reduce memory usage.

  • bpo-38142: The _hashlib OpenSSL wrapper extension module is now PEP-384 compliant.

  • bpo-9216: hashlib constructors now support usedforsecurity flag to signal that a hashing algorithm is not used in a security context.

  • bpo-36991: Fixes a potential incorrect AttributeError exception escaping ZipFile.extract() in some unsupported input error situations.

  • bpo-38134: Remove obsolete copy of PBKDF2_HMAC_fast. All supported OpenSSL versions contain a fast implementation.

  • bpo-38132: The OpenSSL hashlib wrapper uses a simpler implementation. Several Macros and pointless caches are gone. The hash name now comes from OpenSSL's EVP. The algorithm name stays the same, except it is now always lower case.

  • bpo-38008: Fix parent class check in protocols to correctly identify the module that provides a builtin protocol, instead of assuming they all come from the module

  • bpo-34037: For asyncio, add a new coroutine loop.shutdown_default_executor(). The new coroutine provides an API to schedule an executor shutdown that waits on the threadpool to finish closing. Also, has been updated to utilize the new coroutine. Patch by Kyle Stanley.

  • bpo-37405: Fixed regression bug for socket.getsockname() for non-CAN_ISOTP AF_CAN address family sockets by returning a 1-tuple instead of string.

  • bpo-38121: Update parameter names on functions in importlib.metadata matching the changes in the 0.22 release of importlib_metadata.

  • bpo-38110: The os.closewalk() implementation now uses the libc fdwalk() API on platforms where it is available.

  • bpo-38093: Fixes AsyncMock so it doesn't crash when used with AsyncContextManagers or AsyncIterators.

  • bpo-37488: Add warning to datetime.utctimetuple(), datetime.utcnow() and datetime.utcfromtimestamp() .

  • bpo-35640: Allow passing a path-like object as directory argument to the http.server.SimpleHTTPRequestHandler class. Patch by Géry Ogam.

  • bpo-38086: Update importlib.metadata with changes from importlib_metadata 0.21.

  • bpo-37251: Remove __code__ check in AsyncMock that incorrectly evaluated function specs as async objects but failed to evaluate classes with __await__ but no __code__ attribute defined as async objects.

  • bpo-38037: Fix reference counters in the signal module.

  • bpo-38066: Hide internal asyncio.Stream methods: feed_eof(), feed_data(), set_exception() and set_transport().

  • bpo-38059: now uses sys.exit() instead of exit()

  • bpo-38049: Added command-line interface for the ast module.

  • bpo-37953: In typing, improved the __hash__ and __eq__ methods for ForwardReferences.

  • bpo-38026: Fixed inspect.getattr_static() used isinstance while it should avoid dynamic lookup.

  • bpo-35923: Update importlib.machinery.BuiltinImporter to use loader._ORIGIN instead of a hardcoded value. Patch by Dong-hee Na.

  • bpo-38010: In importlib.metadata sync with importlib_metadata 0.20, clarifying behavior of files() and fixing issue where only one requirement was returned for requires() on dist-info packages.

  • bpo-38006: weakref.WeakValueDictionary defines a local remove() function used as callback for weak references. This function was created with a closure. Modify the implementation to avoid the closure.

  • bpo-37995: Added the indent option to ast.dump() which allows it to produce a multiline indented output.

  • bpo-34410: Fixed a crash in the tee() iterator when re-enter it. RuntimeError is now raised in this case.

  • bpo-37140: Fix a ctypes regression of Python 3.8. When a ctypes.Structure is passed by copy to a function, ctypes internals created a temporary object which had the side effect of calling the structure finalizer (__del__) twice. The Python semantics requires a finalizer to be called exactly once. Fix ctypes internals to no longer call the finalizer twice.

  • bpo-37587: _json.scanstring is now up to 3x faster when there are many backslash escaped characters in the JSON string.

  • bpo-37834: Prevent shutil.rmtree exception when built on non-Windows system without fd system call support, like older versions of macOS.

  • bpo-10978: Semaphores and BoundedSemaphores can now release more than one waiting thread at a time.

  • bpo-37972: Subscripts to the objects now receive the same chaining mechanism as any other custom attributes, so that the following usage no longer raises a TypeError:


    Patch by blhsing

  • bpo-37965: Fix C compiler warning caused by distutils.ccompiler.CCompiler.has_function.

  • bpo-37964: Add F_GETPATH command to fcntl.

  • bpo-37960: repr() of buffered and text streams now silences only expected exceptions when get the value of "name" and "mode" attributes.

  • bpo-37961: Add a total_nframe field to the traces collected by the tracemalloc module. This field indicates the original number of frames before it was truncated.

  • bpo-37951: Most features of the subprocess module now work again in subinterpreters. Only preexec_fn is restricted in subinterpreters.

  • bpo-36205: Fix the rusage implementation of time.process_time() to correctly report the sum of the system and user CPU time.

  • bpo-37950: Fix ast.dump() when call with incompletely initialized node.

  • bpo-34679: Restores instantiation of Windows IOCP event loops from the non-main thread.

  • bpo-36917: Add default implementation of the ast.NodeVisitor.visit_Constant() method which emits a deprecation warning and calls corresponding methody visit_Num(), visit_Str(), etc.

  • bpo-37798: Update to verify that the statistics module works well for both C and Python implementations. Patch by Dong-hee Na

  • bpo-26589: Added a new status code to the http module: 451 UNAVAILABLE_FOR_LEGAL_REASONS

  • bpo-37915: Fix a segmentation fault that appeared when comparing instances of datetime.timezone and datetime.tzinfo objects. Patch by Pablo Galindo.

  • bpo-32554: Deprecate having random.seed() call hash on arbitrary types.

  • bpo-9938: Add optional keyword argument exit_on_error for ArgumentParser.

  • bpo-37851: The faulthandler module no longer allocates its alternative stack at Python startup. Now the stack is only allocated at the first faulthandler usage.

  • bpo-32793: Fix a duplicated debug message when smtplib.SMTP.connect() is called.

  • bpo-37885: venv: Don't generate unset variable warning on deactivate.

  • bpo-37868: Fix dataclasses.is_dataclass when given an instance that never raises AttributeError in __getattr__. That is, an object that returns something for __dataclass_fields__ even if it's not a dataclass.

  • bpo-37811: Fix socket module's socket.connect(address) function being unable to establish connection in case of interrupted system call. The problem was observed on all OSes which poll(2) system call can take only non-negative integers and -1 as a timeout value.

  • bpo-37863: Optimizations for Fraction.__hash__ suggested by Tim Peters.

  • bpo-21131: Fix faulthandler.register(chain=True) stack. faulthandler now allocates a dedicated stack of SIGSTKSZ*2 bytes, instead of just SIGSTKSZ bytes. Calling the previous signal handler in faulthandler signal handler uses more than SIGSTKSZ bytes of stack memory on some platforms.

  • bpo-37798: Add C fastpath for statistics.NormalDist.inv_cdf() Patch by Dong-hee Na

  • bpo-37804: Remove the deprecated method threading.Thread.isAlive(). Patch by Dong-hee Na.

  • bpo-37819: Add Fraction.as_integer_ratio() to match the corresponding methods in bool, int, float, and decimal.

  • bpo-14465: Add an xml.etree.ElementTree.indent() function for pretty-printing XML trees. Contributed by Stefan Behnel.

  • bpo-37810: Fix difflib ? hint in diff output when dealing with tabs. Patch by Anthony Sottile.

  • bpo-37772: In zipfile.Path, when adding implicit dirs, ensure that ancestral directories are added and that duplicates are excluded.

  • bpo-18578: Renamed and documented test.bytecode_helper as Patch by Joannah Nanjekye.

  • bpo-37785: Fix xgettext warnings in argparse.

  • bpo-34488: writelines() method of io.BytesIO is now slightly faster when many small lines are passed. Patch by Sergey Fedoseev.

  • bpo-37449: