Python next

Release date: XXXX-XX-XX


  • gh-117187: Fix XML tests for vanilla Expat <2.6.0.


  • gh-116773: Fix instances of <_overlapped.Overlapped object at 0xXXX> still has pending operation at deallocation, the process may crash.

Python 3.9.19 final

Release date: 2024-03-19


Core and Builtins

  • gh-102388: Fix a bug where iso2022_jp_3 and iso2022_jp_2004 codecs read out of bounds


  • gh-115197: urllib.request no longer resolves the hostname before checking it against the system's proxy bypass list on macOS and Windows.

  • gh-115133: Fix tests for XMLPullParser with Expat 2.6.0.

  • gh-81194: Fix a crash in socket.if_indextoname() with specific value (UINT_MAX). Fix an integer overflow in socket.if_indextoname() on 64-bit non-Windows platforms.

  • gh-109858: Protect zipfile from "quoted-overlap" zipbomb. It now raises BadZipFile when try to read an entry that overlaps with other entry or central directory.

  • gh-107077: Seems that in some conditions, OpenSSL will return SSL_ERROR_SYSCALL instead of SSL_ERROR_SSL when a certification verification has failed, but the error parameters will still contain ERR_LIB_SSL and SSL_R_CERTIFICATE_VERIFY_FAILED. We are now detecting this situation and raising the appropiate ssl.SSLCertVerificationError. Patch by Pablo Galindo

  • gh-91133: Fix a bug in tempfile.TemporaryDirectory cleanup, which now no longer dereferences symlinks when working around file system permission errors.


  • gh-115399: Document CVE-2023-52425 of Expat <2.6.0 under "XML vulnerabilities".


  • gh-111239: Update Windows builds to use zlib v1.3.1.

  • gh-109991: Windows builds now use OpenSSL 1.1.1w. Note that OpenSSL 1.1 has reached its end of life and no future fixes will be made, and this version of Python is no longer receiving maintenance fixes and will not be updated to OpenSSL 3.0.


  • gh-109991: Update GitHub CI workflows to use OpenSSL 3.0.11 and multissltests to use 1.1.1w and 3.0.11.

Python 3.9.18 final

Release date: 2023-08-24


  • gh-108310: Fixed an issue where instances of ssl.SSLSocket were vulnerable to a bypass of the TLS handshake and included protections (like certificate verification) and treating sent unencrypted data as if it were post-handshake TLS encrypted data. Security issue reported as CVE-2023-40217 by Aapo Oksman. Patch by Gregory P. Smith.


  • gh-107845: tarfile.data_filter() now takes the location of symlinks into account when determining their target, so it will no longer reject some valid tarballs with LinkOutsideDestinationError.


  • gh-107565: Update multissltests and GitHub CI workflows to use OpenSSL 1.1.1v, 3.0.10, and 3.1.2.


Python 3.9.17 final

Release date: 2023-06-06


  • gh-103142: The version of OpenSSL used in our binary builds has been upgraded to 1.1.1u to address several CVEs.

  • gh-99889: Fixed a security in flaw in uu.decode() that could allow for directory traversal based on the input if no out_file was specified.

  • gh-104049: Do not expose the local on-disk location in directory indexes produced by http.client.SimpleHTTPRequestHandler.

  • gh-102153: urllib.parse.urlsplit() now strips leading C0 control and space characters following the specification for URLs defined by WHATWG in response to CVE-2023-24329. Patch by Illia Volochii.

  • gh-101727: Updated the OpenSSL version used in Windows and macOS binary release builds to 1.1.1t to address CVE-2023-0286, CVE-2022-4303, and CVE-2022-4303 per the OpenSSL 2023-02-07 security advisory.

  • gh-101283: subprocess.Popen now uses a safer approach to find cmd.exe when launching with shell=True. Patch by Eryk Sun, based on a patch by Oleg Iarygin.

Core and Builtins

  • gh-102126: Fix deadlock at shutdown when clearing thread states if any finalizer tries to acquire the runtime head lock. Patch by Kumar Aditya.

  • gh-100892: Fix race while iterating over thread states in clearing threading.local. Patch by Kumar Aditya.



  • gh-100180: Update Windows installer to OpenSSL 1.1.1s


  • gh-103142: Update macOS installer to use OpenSSL 1.1.1u.

Python 3.9.16 final

Release date: 2022-12-06


  • gh-100001: python -m http.server no longer allows terminal control characters sent within a garbage request to be printed to the stderr server log.

    This is done by changing the http.server BaseHTTPRequestHandler .log_message method to replace control characters with a \xHH hex escape before printing.

  • gh-87604: Avoid publishing list of active per-interpreter audit hooks via the gc module

  • gh-98433: The IDNA codec decoder used on DNS hostnames by socket or asyncio related name resolution functions no longer involves a quadratic algorithm. This prevents a potential CPU denial of service if an out-of-spec excessive length hostname involving bidirectional characters were decoded. Some protocols such as urllib http 3xx redirects potentially allow for an attacker to supply such a name.

  • gh-98739: Update bundled libexpat to 2.5.0

  • gh-98517: Port XKCP's fix for the buffer overflows in SHA-3 (CVE-2022-37454).

  • gh-97514: On Linux the multiprocessing module returns to using filesystem backed unix domain sockets for communication with the forkserver process instead of the Linux abstract socket namespace. Only code that chooses to use the "forkserver" start method is affected.

    Abstract sockets have no permissions and could allow any user on the system in the same network namespace (often the whole system) to inject code into the multiprocessing forkserver process. This was a potential privilege escalation. Filesystem based socket permissions restrict this to the forkserver process user as was the default in Python 3.8 and earlier.

    This prevents Linux CVE-2022-42919.

  • gh-68966: The deprecated mailcap module now refuses to inject unsafe text (filenames, MIME types, parameters) into shell commands. Instead of using such text, it will warn and act as if a match was not found (or for test commands, as if the test failed).

Python 3.9.15 final

Release date: 2022-10-11


  • gh-97616: Fix multiplying a list by an integer (list *= int): detect the integer overflow when the new allocated length is close to the maximum size. Issue reported by Jordan Limor. Patch by Victor Stinner.

  • gh-97612: Fix a shell code injection vulnerability in the get-remote-certificate.py example script. The script no longer uses a shell to run openssl commands. Issue reported and initial fix by Caleb Shortt. Patch by Victor Stinner.

Core and Builtins


  • gh-97005: Update bundled libexpat to 2.4.9



  • gh-97897: The macOS 13 SDK includes support for the mkfifoat and mknodat system calls. Using the dir_fd option with either os.mkfifo() or os.mknod() could result in a segfault if cpython is built with the macOS 13 SDK but run on an earlier version of macOS. Prevent this by adding runtime support for detection of these system calls ("weaklinking") as is done for other newer syscalls on macOS.

Python 3.9.14 final

Release date: 2022-09-06


  • gh-95778: Converting between int and str in bases other than 2 (binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now raises a ValueError if the number of digits in string form is above a limit to avoid potential denial of service attacks due to the algorithmic complexity. This is a mitigation for CVE-2020-10735.

    This new limit can be configured or disabled by environment variable, command line flag, or sys APIs. See the integer string conversion length limitation documentation. The default limit is 4300 digits in string form.

    Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

  • gh-87389: http.server: Fix an open redirection vulnerability in the HTTP server when an URI path starts with //. Vulnerability discovered, and initial fix proposed, by Hamza Avvan.

Core and Builtins

  • gh-93065: Fix contextvars HAMT implementation to handle iteration over deep trees.

    The bug was discovered and fixed by Eli Libman. See MagicStack/immutables#84 for more details.


  • gh-94821: Fix binding of unix socket to empty address on Linux to use an available address from the abstract namespace, instead of "0".

  • gh-91810: Suppress writing an XML declaration in open files in ElementTree.write() with encoding='unicode' and xml_declaration=None.

  • bpo-45393: Fix the formatting for await x and not x in the operator precedence table when using the help() system.

  • bpo-46197: Fix ensurepip environment isolation for subprocess running pip.


  • gh-95280: Fix problem with test_ssl test_get_ciphers on systems that require perfect forward secrecy (PFS) ciphers.

  • gh-94208: test_ssl is now checking for supported TLS version and protocols in more tests.

  • bpo-47016: Create a GitHub Actions workflow for verifying bundled pip and setuptools. Patch by Illia Volochii and Adam Turner.

Python 3.9.13 final

Release date: 2022-05-17

Core and Builtins

  • gh-92311: Fixed a bug where setting frame.f_lineno to jump over a list comprehension could misbehave or crash.

  • gh-92112: Fix crash triggered by an evil custom mro() on a metaclass.

  • gh-92036: Fix a crash in subinterpreters related to the garbage collector. When a subinterpreter is deleted, untrack all objects tracked by its GC. To prevent a crash in deallocator functions expecting objects to be tracked by the GC, leak a strong reference to these objects on purpose, so they are never deleted and their deallocator functions are not called. Patch by Victor Stinner.

  • gh-91421: Fix a potential integer overflow in _Py_DecodeUTF8Ex.

  • bpo-46775: Some Windows system error codes(>= 10000) are now mapped into the correct errno and may now raise a subclass of OSError. Patch by Dong-hee Na.

  • bpo-46962: Classes and functions that unconditionally declared their docstrings ignoring the --without-doc-strings compilation flag no longer do so.

    The classes affected are pickle.PickleBuffer, testcapi.RecursingInfinitelyError, and types.GenericAlias.

    The functions affected are 24 methods in ctypes.

    Patch by Oleg Iarygin.

  • bpo-36819: Fix crashes in built-in encoders with error handlers that return position less or equal than the starting position of non-encodable characters.


  • gh-91581: utcfromtimestamp() no longer attempts to resolve fold in the pure Python implementation, since the fold is never 1 in UTC. In addition to being slightly faster in the common case, this also prevents some errors when the timestamp is close to datetime.min. Patch by Paul Ganssle.

  • gh-92530: Fix an issue that occurred after interrupting threading.Condition.notify().

  • gh-92049: Forbid pickling constants re._constants.SUCCESS etc. Previously, pickling did not fail, but the result could not be unpickled.

  • bpo-47029: Always close the read end of the pipe used by multiprocessing.Queue after the last write of buffered data to the write end of the pipe to avoid BrokenPipeError at garbage collection and at multiprocessing.Queue.close() calls. Patch by Géry Ogam.

  • gh-91910: Add missing f prefix to f-strings in error messages from the multiprocessing and asyncio modules.

  • gh-91810: ElementTree method write() and function tostring() now use the text file's encoding ("UTF-8" if not available) instead of locale encoding in XML declaration when encoding="unicode" is specified.

  • gh-91832: Add required attribute to argparse.Action repr output.

  • gh-91734: Fix OSS audio support on Solaris.

  • gh-91700: Compilation of regular expression containing a conditional expression (?(group)...) now raises an appropriate re.error if the group number refers to not defined group. Previously an internal RuntimeError was raised.

  • gh-91676: Fix unittest.IsolatedAsyncioTestCase to shutdown the per test event loop executor before returning from its run method so that a not yet stopped or garbage collected executor state does not persist beyond the test.

  • gh-90568: Parsing \N escapes of Unicode Named Character Sequences in a regular expression raises now re.error instead of TypeError.

  • gh-91595: Fix the comparison of character and integer inside Tools.gdb.libpython.write_repr(). Patch by Yu Liu.

  • gh-90622: Worker processes for concurrent.futures.ProcessPoolExecutor are no longer spawned on demand (a feature added in 3.9) when the multiprocessing context start method is "fork" as that can lead to deadlocks in the child processes due to a fork happening while threads are running.

  • gh-91575: Update case-insensitive matching in the re module to the latest Unicode version.

  • gh-91581: Remove an unhandled error case in the C implementation of calls to datetime.fromtimestamp with no time zone (i.e. getting a local time from an epoch timestamp). This should have no user-facing effect other than giving a possibly more accurate error message when called with timestamps that fall on 10000-01-01 in the local time. Patch by Paul Ganssle.

  • bpo-34480: Fix a bug where _markupbase raised an UnboundLocalError when an invalid keyword was found in marked section. Patch by Marek Suscak.

  • bpo-27929: Fix asyncio.loop.sock_connect() to only resolve names for socket.AF_INET or socket.AF_INET6 families. Resolution may not make sense for other families, like socket.AF_BLUETOOTH and socket.AF_UNIX.

  • bpo-43323: Fix errors in the email module if the charset itself contains undecodable/unencodable characters.

  • bpo-46787: Fix concurrent.futures.ProcessPoolExecutor exception memory leak

  • bpo-46415: Fix ipaddress.ip_{address,interface,network} raising TypeError instead of ValueError if given invalid tuple as address parameter.

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

  • bpo-44493: Add missing terminated NUL in sockaddr_un's length

    This was potentially observable when using non-abstract AF_UNIX datagram sockets to processes written in another programming language.

  • bpo-42627: Fix incorrect parsing of Windows registry proxy settings

  • bpo-36073: Raise ProgrammingError instead of segfaulting on recursive usage of cursors in sqlite3 converters. Patch by Sergey Fedoseev.




  • bpo-47103: Windows PGInstrument builds now copy a required DLL into the output directory, making it easier to run the profile stage of a PGO build.


  • bpo-47194: Update zlib to v1.2.12 to resolve CVE-2018-25032.

  • bpo-46785: Fix race condition between os.stat() and unlinking a file on Windows, by using errors codes returned by FindFirstFileW() when appropriate in win32_xstat_impl.

  • bpo-40859: Update Windows build to use xz-5.2.5


  • gh-91583: Fix regression in the code generated by Argument Clinic for functions with the defining_class parameter.

Python 3.9.12 final

Release date: 2022-03-23

Core and Builtins

  • bpo-46968: Check for the existence of the "sys/auxv.h" header in faulthandler to avoid compilation problems in systems where this header doesn't exist. Patch by Pablo Galindo


  • bpo-47101: hashlib.algorithms_available now lists only algorithms that are provided by activated crypto providers on OpenSSL 3.0. Legacy algorithms are not listed unless the legacy provider has been loaded into the default OSSL context.

  • bpo-23691: Protect the re.finditer() iterator from re-entering.

  • bpo-42369: Fix thread safety of zipfile._SharedFile.tell() to avoid a "zipfile.BadZipFile: Bad CRC-32 for file" exception when reading a ZipFile from multiple threads.

  • bpo-38256: Fix binascii.crc32() when it is compiled to use zlib'c crc32 to work properly on inputs 4+GiB in length instead of returning the wrong result. The workaround prior to this was to always feed the function data in increments smaller than 4GiB or to just call the zlib module function.

  • bpo-39394: A warning about inline flags not at the start of the regular expression now contains the position of the flag.

  • bpo-47061: Deprecate the various modules listed by PEP 594:

    aifc, asynchat, asyncore, audioop, cgi, cgitb, chunk, crypt, imghdr, msilib, nntplib, nis, ossaudiodev, pipes, smtpd, sndhdr, spwd, sunau, telnetlib, uu, xdrlib

  • bpo-2604: Fix bug where doctests using globals would fail when run multiple times.

  • bpo-45997: Fix asyncio.Semaphore re-aquiring FIFO order.

  • bpo-47022: The asynchat, asyncore and smtpd modules have been deprecated since at least Python 3.6. Their documentation has now been updated to note they will removed in Python 3.12 (PEP 594).

  • bpo-46421: Fix a unittest issue where if the command was invoked as python -m unittest and the filename(s) began with a dot (.), a ValueError is returned.

  • bpo-40296: Fix supporting generic aliases in pydoc.

  • bpo-14156: argparse.FileType now supports an argument of '-' in binary mode, returning the .buffer attribute of sys.stdin/sys.stdout as appropriate. Modes including 'x' and 'a' are treated equivalently to 'w' when argument is '-'. Patch contributed by Josh Rosenberg

Python 3.9.11 final

Release date: 2022-03-16

Core and Builtins

  • bpo-46852: Rename the private undocumented float.__set_format__() method to float.__setformat__() to fix a typo introduced in Python 3.7. The method is only used by test_float. Patch by Victor Stinner.

  • bpo-46794: Bump up the libexpat version into 2.4.6

  • bpo-46762: Fix an assert failure in debug builds when a '<', '>', or '=' is the last character in an f-string that's missing a closing right brace.

  • bpo-46732: Correct the docstring for the __bool__() method. Patch by Jelle Zijlstra.

  • bpo-40479: Add a missing call to va_end() in Modules/_hashopenssl.c.

  • bpo-46615: When iterating over sets internally in setobject.c, acquire strong references to the resulting items from the set. This prevents crashes in corner-cases of various set operations where the set gets mutated.

  • bpo-43721: Fix docstrings of getter, setter, and deleter to clarify that they create a new copy of the property.

  • bpo-46503: Fix an assert when parsing some invalid N escape sequences in f-strings.

  • bpo-46417: Fix a race condition on setting a type __bases__ attribute: the internal function add_subclass() now gets the PyTypeObject.tp_subclasses member after calling PyWeakref_NewRef() which can trigger a garbage collection which can indirectly modify PyTypeObject.tp_subclasses. Patch by Victor Stinner.

  • bpo-46383: Fix invalid signature of _zoneinfo's module_free function to resolve a crash on wasm32-emscripten platform.


  • bpo-43253: Fix a crash when closing transports where the underlying socket handle is already invalid on the Proactor event loop.

  • bpo-47004: Apply bugfixes from importlib_metadata 4.11.3, including bugfix for EntryPoint.extras, which was returning match objects and not the extras strings.

  • bpo-46985: Upgrade pip wheel bundled with ensurepip (pip 22.0.4)

  • bpo-46968: faulthandler: On Linux 5.14 and newer, dynamically determine size of signal handler stack size CPython allocates using getauxval(AT_MINSIGSTKSZ). This changes allows for Python extension's request to Linux kernel to use AMX_TILE instruction set on Sapphire Rapids Xeon processor to succeed, unblocking use of the ISA in frameworks.

  • bpo-46955: Expose asyncio.base_events.Server as asyncio.Server. Patch by Stefan Zabka.

  • bpo-46932: Update bundled libexpat to 2.4.7

  • bpo-25707: Fixed a file leak in xml.etree.ElementTree.iterparse() when the iterator is not exhausted. Patch by Jacob Walls.

  • bpo-44886: Inherit asyncio proactor datagram transport from asyncio.DatagramTransport.

  • bpo-46827: Support UDP sockets in asyncio.loop.sock_connect() for selector-based event loops. Patch by Thomas Grainger.

  • bpo-46811: Make test suite support Expat >=2.4.5

  • bpo-46252: Raise TypeError if ssl.SSLSocket is passed to transport-based APIs.

  • bpo-46784: Fix libexpat symbols collisions with user dynamically loaded or statically linked libexpat in embedded Python.

  • bpo-39327: shutil.rmtree() can now work with VirtualBox shared folders when running from the guest operating-system.

  • bpo-46756: Fix a bug in urllib.request.HTTPPasswordMgr.find_user_password() and urllib.request.HTTPPasswordMgrWithPriorAuth.is_authenticated() which allowed to bypass authorization. For example, access to URI example.org/foobar was allowed if the user was authorized for URI example.org/foo.

  • bpo-45863: When the tarfile module creates a pax format archive, it will put an integer representation of timestamps in the ustar header (if possible) for the benefit of older unarchivers, in addition to the existing full-precision timestamps in the pax extended header.

  • bpo-46672: Fix NameError in asyncio.gather() when initial type check fails.

  • bpo-45948: Fixed a discrepancy in the C implementation of the xml.etree.ElementTree module. Now, instantiating an xml.etree.ElementTree.XMLParser with a target=None keyword provides a default xml.etree.ElementTree.TreeBuilder target as the Python implementation does.

  • bpo-46591: Make the IDLE doc URL on the About IDLE dialog clickable.

  • bpo-46400: expat: Update libexpat from 2.4.1 to 2.4.4

  • bpo-46487: Add the get_write_buffer_limits method to asyncio.transports.WriteTransport and to the SSL transport.

  • bpo-46539: In typing.get_type_hints(), support evaluating stringified ClassVar and Final annotations inside Annotated. Patch by Gregory Beauregard.

  • bpo-46491: Allow typing.Annotated to wrap typing.Final and typing.ClassVar. Patch by Gregory Beauregard.

  • bpo-46436: Fix command-line option -d/--directory in module http.server which is ignored when combined with command-line option --cgi. Patch by Géry Ogam.

  • bpo-41403: Make mock.patch() raise a TypeError with a relevant error message on invalid arg. Previously it allowed a cryptic AttributeError to escape.

  • bpo-46474: In importlib.metadata.EntryPoint.pattern, avoid potential REDoS by limiting ambiguity in consecutive whitespace.

  • bpo-46469: asyncio generic classes now return types.GenericAlias in __class_getitem__ instead of the same class.

  • bpo-46434: pdb now gracefully handles help when __doc__ is missing, for example when run with pregenerated optimized .pyc files.

  • bpo-46333: The __eq__() and __hash__() methods of typing.ForwardRef now honor the module parameter of typing.ForwardRef. Forward references from different modules are now differentiated.

  • bpo-43118: Fix a bug in inspect.signature() that was causing it to fail on some subclasses of classes with a __text_signature__ referencing module globals. Patch by Weipeng Hong.

  • bpo-21987: Fix an issue with tarfile.TarFile.getmember() getting a directory name with a trailing slash.

  • bpo-20392: Fix inconsistency with uppercase file extensions in MimeTypes.guess_type(). Patch by Kumar Aditya.

  • bpo-46080: Fix exception in argparse help text generation if a argparse.BooleanOptionalAction argument's default is argparse.SUPPRESS and it has help specified. Patch by Felix Fontein.

  • bpo-44439: Fix .write() method of a member file in ZipFile, when the input data is an object that supports the buffer protocol, the file length may be wrong.

  • bpo-45703: When a namespace package is imported before another module from the same namespace is created/installed in a different sys.path location while the program is running, calling the importlib.invalidate_caches() function will now also guarantee the new module is noticed.

  • bpo-24959: Fix bug where unittest sometimes drops frames from tracebacks of exceptions raised in tests.


  • bpo-46463: Fixes escape4chm.py script used when building the CHM documentation file


  • bpo-46913: Fix test_faulthandler.test_sigfpe() if Python is built with undefined behavior sanitizer (UBSAN): disable UBSAN on the faulthandler_sigfpe() function. Patch by Victor Stinner.

  • bpo-46708: Prevent default asyncio event loop policy modification warning after test_asyncio execution.

  • bpo-46616: Ensures test_importlib.test_windows cleans up registry keys after completion.

  • bpo-44359: test_ftplib now silently ignores socket errors to prevent logging unhandled threading exceptions. Patch by Victor Stinner.

  • bpo-46542: Fix a Python crash in test_lib2to3 when using Python built in debug mode: limit the recursion limit. Patch by Victor Stinner.

  • bpo-46576: test_peg_generator now disables compiler optimization when testing compilation of its own C extensions to significantly speed up the testing on non-debug builds of CPython.

  • bpo-46542: Fix test_json tests checking for RecursionError: modify these tests to use support.infinite_recursion(). Patch by Victor Stinner.

  • bpo-13886: Skip test_builtin PTY tests on non-ASCII characters if the readline module is loaded. The readline module changes input() behavior, but test_builtin is not intented to test the readline module. Patch by Victor Stinner.


  • bpo-47024: Update OpenSSL to 1.1.1n for macOS installers and all Windows builds.

  • bpo-38472: Fix GCC detection in setup.py when cross-compiling. The C compiler is now run with LC_ALL=C. Previously, the detection failed with a German locale.

  • bpo-46513: configure no longer uses AC_C_CHAR_UNSIGNED macro and pyconfig.h no longer defines reserved symbol __CHAR_UNSIGNED__.

  • bpo-45925: Update Windows installer to use SQLite 3.37.2.

  • bpo-47032: Ensure Windows install builds fail correctly with a non-zero exit code when part of the build fails.


  • bpo-44549: Update bzip2 to 1.0.8 in Windows builds to mitigate CVE-2016-3189 and CVE-2019-12900

  • bpo-46948: Prevent CVE-2022-26488 by ensuring the Add to PATH option in the Windows installer uses the correct path when being repaired.

  • bpo-46638: Ensures registry virtualization is consistently disabled. For 3.10 and earlier, it remains enabled (some registry writes are protected), while for 3.11 and later it is disabled (registry modifications affect all applications).


  • bpo-45925: Update macOS installer to SQLite 3.37.2.


  • bpo-46630: Make query dialogs on Windows start with a cursor in the entry box.

  • bpo-45296: Clarify close, quit, and exit in IDLE. In the File menu, 'Close' and 'Exit' are now 'Close Window' (the current one) and 'Exit' is now 'Exit IDLE' (by closing all windows). In Shell, 'quit()' and 'exit()' mean 'close Shell'. If there are no other windows, this also exits IDLE.

  • bpo-45447: Apply IDLE syntax highlighting to pyi files. Patch by Alex Waygood and Terry Jan Reedy.

Python 3.9.10 final

Release date: 2022-01-13

Core and Builtins

  • bpo-46070: Py_EndInterpreter() now explicitly untracks all objects currently tracked by the GC. Previously, if an object was used later by another interpreter, calling PyObject_GC_UnTrack() on the object crashed if the previous or the next object of the PyGC_Head structure became a dangling pointer. Patch by Victor Stinner.

  • bpo-46085: Fix iterator cache mechanism of OrderedDict.

  • bpo-46110: Add a maximum recursion check to the PEG parser to avoid stack overflow. Patch by Pablo Galindo

  • bpo-46000: Improve compatibility of the curses module with NetBSD curses.

  • bpo-45614: Fix traceback display for exceptions with invalid module name.

  • bpo-45806: Re-introduced fix that allows recovery from stack overflow without crashing the interpreter. The original fix as part of bpo-42500 was reverted (see release notes for Python 3.9.4) since it introduced an ABI change in a bugfix release which is not allowed. The new fix doesn't introduce any ABI changes. Patch by Mark Shannon.

  • bpo-45822: Fixed a bug in the parser that was causing it to not respect PEP 263 coding cookies when no flags are provided. Patch by Pablo Galindo

  • bpo-45820: Fix a segfault when the parser fails without reading any input. Patch by Pablo Galindo

  • bpo-42540: Fix crash when os.fork() is called with an active non-default memory allocator.


  • bpo-40479: Fix hashlib usedforsecurity option to work correctly with OpenSSL 3.0.0 in FIPS mode.

  • bpo-46070: Fix possible segfault when importing the asyncio module from different sub-interpreters in parallel. Patch by Erlend E. Aasland.

  • bpo-46278: Reflect context argument in AbstractEventLoop.call_*() methods. Loop implementations already support it.

  • bpo-46239: Improve error message when importing asyncio.windows_events on non-Windows.

  • bpo-20369: concurrent.futures.wait() no longer blocks forever when given duplicate Futures. Patch by Kumar Aditya.

  • bpo-46105: Honor spec when generating requirement specs with urls and extras (importlib_metadata 4.8.3).

  • bpo-26952: argparse raises ValueError with clear message when trying to render usage for an empty mutually-exclusive group. Previously it raised a cryptic IndexError.

  • bpo-27718: Fix help for the signal module. Some functions (e.g. signal() and getsignal()) were omitted.

  • bpo-46032: The registry() method of functools.singledispatch() functions checks now the first argument or the first parameter annotation and raises a TypeError if it is not supported. Previously unsupported "types" were ignored (e.g. typing.List[int]) or caused an error at calling time (e.g. list[int]).

  • bpo-46018: Ensure that math.expm1() does not raise on underflow.

  • bpo-27946: Fix possible crash when getting an attribute of class:xml.etree.ElementTree.Element simultaneously with replacing the attrib dict.

  • bpo-13236: unittest.TextTestResult and unittest.TextTestRunner flush now the output stream more often.

  • bpo-37658: Fix issue when on certain conditions asyncio.wait_for() may allow a coroutine to complete successfully, but fail to return the result, potentially causing memory leaks or other issues.

  • bpo-45831: faulthandler can now write ASCII-only strings (like filenames and function names) with a single write() syscall when dumping a traceback. It reduces the risk of getting an unreadable dump when two threads or two processes dump a traceback to the same file (like stderr) at the same time. Patch by Victor Stinner.

  • bpo-41735: Fix thread lock in zlib.Decompress.flush() method before PyObject_GetBuffer.

  • bpo-45664: Fix types.resolve_bases() and types.new_class() for types.GenericAlias instance as a base.

  • bpo-45663: Fix dataclasses.is_dataclass() for dataclasses which are subclasses of types.GenericAlias.

  • bpo-45662: Fix the repr of dataclasses.InitVar with a type alias to the built-in class, e.g. InitVar[list[int]].

  • bpo-43498: Avoid a possible "RuntimeError: dictionary changed size during iteration" when adjusting the process count of ProcessPoolExecutor.

  • 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-19737: Update the documentation for the globals() function.

  • bpo-45840: Improve cross-references in the documentation for the data model.

  • bpo-45788: Link doc for sys.prefix to sysconfig doc on installation paths.

  • bpo-25381: In the extending chapter of the extending doc, update a paragraph about the global variables containing exception information.

  • bpo-43905: Expanded astuple() and asdict() docs, warning about deepcopy being applied and providing a workaround.

  • bpo-41028: Language and version switchers, previously maintained in every cpython branches, are now handled by docsbuild-script.



  • bpo-46263: configure no longer sets MULTIARCH on FreeBSD platforms.

  • bpo-46106: Updated OpenSSL to 1.1.1m in Windows builds, macOS installer builds, and CI. Patch by Kumar Aditya.

  • bpo-44035: CI now verifies that autoconf files have been regenerated with a current and unpatched autoconf package.

  • bpo-33393: Update config.guess to 2021-06-03 and config.sub to 2021-08-14. Makefile now has an update-config target to make updating more convenient.

  • bpo-45866: make regen-all now produces the same output when run from a directory other than the source tree: when building Python out of the source tree. pegen now strips directory of the "generated by pygen from <FILENAME>" header Patch by Victor Stinner.

  • bpo-41498: Python now compiles on platforms without sigset_t. Several functions in signal are not available when sigset_t is missing.

    Based on patch by Roman Yurchak for pyodide.

  • bpo-45881: setup.py now uses CC from environment first to discover multiarch and cross compile paths.


  • bpo-45901: When installed through the Microsoft Store and set as the default app for *.py files, command line arguments will now be passed to Python when invoking a script without explicitly launching Python (that is, script.py args rather than python script.py args).


  • bpo-40477: The Python Launcher app for macOS now properly launches scripts and, if necessary, the Terminal app when running on recent macOS releases.

  • bpo-45732: Update python.org macOS installer to use Tcl/Tk 8.6.12.


  • bpo-45838: Fix line number calculation when debugging Python with GDB.


  • bpo-39026: Fix Python.h to build C extensions with Xcode: remove a relative include from Include/cpython/pystate.h.

Python 3.9.9 final

Release date: 2021-11-15

Core and Builtins

  • bpo-45738: Fix computation of error location for invalid continuation characters in the parser. Patch by Pablo Galindo.


  • bpo-45235: Reverted an argparse bugfix that caused regression in the handling of default arguments for subparsers. This prevented leaf level arguments from taking precedence over root level arguments.

  • bpo-45765: In importlib.metadata, fix distribution discovery for an empty path.

  • bpo-45644: In-place JSON file formatting using python3 -m json.tool infile infile now works correctly, previously it left the file empty. Patch by Chris Wesseling.


  • bpo-45772: socket.socket documentation is corrected to a class from a function.

  • bpo-45392: Update the docstring of the type built-in to remove a redundant line and to mention keyword arguments for the constructor.


  • bpo-45732: Updates bundled Tcl/Tk to 8.6.12.

  • bpo-45720: Internal reference to shlwapi.dll was dropped to help improve startup time. This DLL will no longer be loaded at the start of every Python process.

Python 3.9.8 final

Release date: 2021-11-05

Core and Builtins

  • bpo-30570: Fixed a crash in issubclass() from infinite recursion when searching pathological __bases__ tuples.

  • bpo-45494: Fix parser crash when reporting errors involving invalid continuation characters. 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, io.open() in text mode is also affected. This change solves a deadlock in os.isatty(). Patch by Vincent Michel in bpo-44219.

  • bpo-44959: Added fallback to extension modules with '.sl' suffix on HP-UX

  • 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-45678: Fix bug in Python 3.9 that meant functools.singledispatchmethod failed to properly wrap the attributes of the target method. Patch by Alex Waygood.

  • bpo-45679: Fix caching of multi-value typing.Literal. Literal[True, 2] is no longer equal to Literal[1, 2].

  • bpo-45438: Fix typing.Signature string representation for generic builtin types.

  • bpo-45581: sqlite3.connect() now correctly raises MemoryError if the underlying SQLite API signals memory error. Patch by Erlend E. Aasland.

  • bpo-39679: Fix bug in functools.singledispatchmethod that caused it to fail when attempting to register a classmethod() or staticmethod() using type annotations. Patch contributed by Alex Waygood.

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

  • 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-44904: Fix bug in the doctest module that caused it to fail if a docstring included an example with a classmethod property. Patch by Alex Waygood.

  • bpo-45406: Make inspect.getmodule() catch FileNotFoundError raised by :'func:inspect.getabsfile, and return None to indicate that the module could not be determined.

  • 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-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-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-45160: When tracing a tkinter variable used by a ttk OptionMenu, callbacks are no longer made twice.

  • 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-45097: Remove deprecation warnings about the loop argument in asyncio incorrectly emitted in cases when the user does not pass the loop argument.

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

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

  • bpo-39039: tarfile.open 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-45726: Improve documentation for functools.singledispatch() and functools.singledispatchmethod.

  • bpo-45680: Amend the docs on GenericAlias objects to clarify that non-container classes can also implement __class_getitem__. Patch contributed by Alex Waygood.

  • bpo-45655: Add a new "relevant PEPs" section to the top of the documentation for the typing module. Patch by Alex Waygood.

  • bpo-45604: Add level argument to multiprocessing.log_to_stderr function docs.

  • 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 collections.abc.

  • bpo-45516: Add protocol description to the importlib.abc.Traversable documentation.

  • 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-45578: Add tests for dis.distb()

  • bpo-45577: Add subtests for all pickle protocols in test_zoneinfo.

  • bpo-43592: test.libregrtest now raises the soft resource limit for the maximum number of file descriptors when the default is too low for our test suite as was often the case on macOS.

  • bpo-40173: Fix test.support.import_helper.import_fresh_module().

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


  • bpo-43158: setup.py now uses values from configure script to build the _uuid extension module. Configure now detects util-linux's libuuid, too.

  • bpo-45571: Modules/Setup now use PY_CFLAGS_NODIST instead of PY_CFLAGS to compile shared modules.

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

  • 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-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-44828: Avoid tkinter file dialog failure on macOS 12 Monterey when using the Tk 8.6.11 provided by python.org macOS installers. Patch by Marc Culler of the Tk project.


  • 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-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 3.9.7 final

Release date: 2021-08-30


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

  • 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.

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

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

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

  • 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-44472: Fix ltrace functionality when exceptions are raised. 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-39091: Fix crash when using passing a non-exception to a generator's throw() method. Patch by Noah Oxer


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

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

  • bpo-44815: Always show loop= arg deprecations in asyncio.gather() and asyncio.sleep()

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

  • 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-42853: Fix http.client.HTTPSConnection fails to download >2GiB data.

  • 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 collections.abc.Set._hash() now matches that of frozenset.__hash__().

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

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

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

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

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

  • 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-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-43048: Handle RecursionError in TracebackException's constructor, so that long exceptions chains are truncated instead of causing traceback formatting to fail.

  • 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 tarfile.open() 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-30256: Pass multiprocessing BaseProxy argument manager_owned through AutoProxy.

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

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

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


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

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

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

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

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

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

  • 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-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-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-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.



  • 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 3.9.6 final

Release date: 2021-06-28


  • 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-44409: Fix error location information for tokenizer errors raised on initialization of the tokenizer. 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-44168: Fix error message in the parser involving keyword arguments with invalid expressions. Patch by Pablo Galindo

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

  • bpo-44070: No longer eagerly makes import filenames absolute, except for extension modules, which was introduced in 3.9.5.

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

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


  • bpo-44516: Update vendored pip to 21.1.3

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

  • 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 libgcc_s.so file (ex: EMFILE error). 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-44395: Fix as_string() to pass unixfrom properly. Patch by Dong-hee Na.

  • bpo-44342: [Enum] Be more robust in searching for pickle support before making an enum class unpicklable.

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

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

  • 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-44061: Fix regression in previous release when calling pkgutil.iter_modules() with a list of pathlib.Path objects

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

  • bpo-43666: AIX: Lib/_aix_support.get_platform() may fail in an AIX WPAR. The fileset bos.rte appears to have a builddate in both LPAR and WPAR so this fileset is queried rather than bos.mp64. To prevent a similiar situation (no builddate in ODM) a value (9988) sufficient for completing a build is provided. Patch by M Felt.

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

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

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

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


  • 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-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 typing.io and typing.re 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-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-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 test.support.SHORT_TIMEOUT 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-44363: Account for address sanitizer in test_capi. test_capi now passes when run GCC address sanitizer.


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



  • bpo-43568: Relax unnecessarily restrictive MACOSX_DEPLOYMENT_TARGET check when building extension modules for macOS. Patch by Joshua Root.

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


  • 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.

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

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


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


Python 3.9.5 final

Release date: 2021-05-03


  • bpo-43434: Creating a sqlite3.Connection object now also produces a sqlite3.connect auditing event. Previously this event was only produced by sqlite3.connect() calls. Patch by Erlend E. Aasland.

  • 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-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.

Core and Builtins

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

  • 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-43993: Update bundled pip to 21.1.1.

  • 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-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-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-42248: [Enum] ensure exceptions raised in _missing_ are released.

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

  • 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 make_ssl_data.py script has been rewritten to use OpenSSL's text file with error codes.

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

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

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

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

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

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

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


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

Python 3.9.4 final

Release date: 2021-04-04

Core and Builtins

  • bpo-43710: Reverted the fix for https://bugs.python.org/issue42500 as it changed the PyThreadState struct size and broke the 3.9.x ABI in the 3.9.3 release (visible on 32-bit platforms using binaries compiled using an earlier version of Python 3.9.x headers).


  • 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.

Python 3.9.3 final

Release date: 2021-04-02


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

  • bpo-42500: Improve handling of exceptions near recursion limit. Converts a number of Fatal Errors in RecursionErrors.


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

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

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

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

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

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

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

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



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


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

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


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


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

  • 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.

Python 3.9.2 final

Release date: 2021-02-19


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

Python 3.9.2 release candidate 1

Release date: 2021-02-16


Core and Builtins


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

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

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

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

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

  • bpo-42851: remove __init_subclass__ support for Enum members

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

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

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

  • bpo-42517: Enum: private names will raise a DeprecationWarning; in 3.10 they will become normal attributes

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

  • bpo-42532: Remove unexpected call of __bool__ when passing a spec_arg argument to a Mock.

  • 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-42375: subprocess module update for DragonFlyBSD support.

  • 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-42318: Fixed support of non-BMP characters in tkinter on macOS.

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

  • 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-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-39101: Fixed tests using IsolatedAsyncioTestCase from hanging on BaseExceptions.

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

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

  • bpo-41889: Enum: fix regression involving inheriting a multiply-inherited enum

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

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

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

  • bpo-40084: Fix Enum.__dir__: dir(Enum.member) now includes attributes as well as methods.

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

  • 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-17140: Add documentation for the multiprocessing.pool.ThreadPool class.


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

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


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

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

  • 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 ".cpython-310d.so" instead of ".so"). Previosuly 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-29076: Add fish shell support to macOS installer.


  • 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-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-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-42726: Fixed Python 3 compatibility issue with gdb/libpython.py handling of attribute dictionaries.

  • bpo-42613: Fix freeze.py tool to use the prope config and library directories. Patch by Victor Stinner.


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

  • 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-40052: Fix an alignment build warning/error in function PyVectorcall_Function(). Patch by Andreas Schneider, Antoine Pitrou and Petr Viktorin.

Python 3.9.1 final

Release date: 2020-12-07

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-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-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-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-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-34215: Clarify the error message for asyncio.IncompleteReadError when expected is None.

  • 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-41116: If no explicit macOS SDK was specified, setup.py should check for Tcl and TK frameworks in /Library/Frameworks; the previous commit inadvertently broke that test.

  • bpo-42504: Fix build on macOS Big Sur when MACOSX_DEPLOYMENT_TARGET=11


  • 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.

Python 3.9.1 release candidate 1

Release date: 2020-11-24


  • 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.

  • bpo-40791: Add volatile to the accumulator variable in hmac.compare_digest, making constant-time-defeating optimizations less likely.

Core and Builtins

  • 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-42374: Fix a regression introduced by the new parser, where an unparenthesized walrus operator was not allowed within generator expressions.

  • 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-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-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-42057: Fix peephole optimizer misoptimize conditional jump + JUMP_IF_NOT_EXC_MATCH pair.

  • 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-41909: Fixed stack overflow in issubclass() and isinstance() when getting the __bases__ attribute leads to infinite recursion.

  • 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-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-42328: Fixed tkinter.ttk.Style.map(). The function accepts now the representation of the default state as empty sequence (as returned by Style.map()). 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-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-42014: The onerror callback from shutil.rmtree now receives correct function when os.open fails.

  • bpo-42237: Fix os.sendfile() on illumos.

  • bpo-42249: Fixed writing binary Plist files larger than 4 GiB.

  • 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-41754: webbrowser: Ignore NotADirectoryError when calling xdg-settings.

  • bpo-29566: binhex.binhex() consistently writes macOS 9 line endings.

  • 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-42146: Fix memory leak in subprocess.Popen() in case an uid (gid) specified in user (group, extra_groups) overflows uid_t (gid_t).

  • bpo-42140: Improve asyncio.wait function to create the futures set just one time.

  • 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-41052: Pickling heap types implemented in C with protocols 0 and 1 raises now an error instead of producing incorrect data.

  • 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-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-41900: C14N 2.0 serialisation in xml.etree.ElementTree failed for unprefixed attributes when a default namespace was defined.

  • 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-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-41817: fix tkinter.EventType Enum so all members are strings, and none are tuples

  • bpo-41815: Fix SQLite3 segfault when backing up closed database. Patch contributed by Peter David McCormick.

  • bpo-41316: Fix the tarfile module to write only basename of TAR file to GZIP compression header.

  • bpo-16396: Allow ctypes.wintypes to be imported on non-Windows systems.

  • bpo-40592: shutil.which() now ignores empty entries in PATHEXT instead of treating them as a match.

  • bpo-40550: Fix time-of-check/time-of-action issue in subprocess.Popen.send_signal.

  • 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-40105: ZipFile truncates files to avoid corruption when a shorter comment is provided in append ("a") mode. Patch by Jan Mazur.

  • bpo-27321: Fixed KeyError exception when flattening an email to a string attempts to replace a non-existent Content-Transfer-Encoding header.


  • bpo-42153: Fix the URL for the IMAP protocol documents.

  • bpo-42061: Document __format__ functionality for IP addresses.

  • bpo-41910: Document the default implementation of object.__eq__.

  • bpo-42010: Clarify that subscription expressions are also valid for certain classes and types in the standard library, and for user-defined classes and types if the classmethod __class_getitem__() is provided.

  • bpo-41805: Documented generic alias type and types.GenericAlias. Also added an entry in glossary for generic types.

  • 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-41726: Update the refcounts info of PyType_FromModuleAndSpec.

  • bpo-39693: Fix tarfile's extractfile documentation

  • bpo-39416: Document some restrictions on the default string representations of numeric classes.


  • bpo-40754: Include _testinternalcapi module in Windows installer for test suite

  • 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-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-41561: test_ssl: skip test_min_max_version_mismatch when TLS 1.0 is not available

  • bpo-41602: Add tests for SIGINT handling in the runpy module.

  • bpo-41306: Fixed a failure in test_tk.test_widgets.ScaleTest happening when executing the test with Tk 8.6.10.


  • bpo-42398: Fix a race condition in "make regen-all" when make -jN option is used to run jobs in parallel. The clinic.py 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-38249: Update Py_UNREACHABLE to use __builtin_unreachable() if only the compiler is able to use it. Patch by Dong-hee Na.

  • bpo-40998: Addressed three compiler warnings found by undefined behavior sanitizer (ubsan).


  • bpo-42120: Remove macro definition of copysign (to _copysign) in headers.

  • bpo-38439: Updates the icons for IDLE in the Windows Store package.

  • bpo-41744: Fixes automatic import of props file when using the Nuget package.

  • bpo-41557: Update Windows installer to use SQLite 3.33.0.

  • bpo-38324: Avoid Unicode errors when accessing certain locale data on Windows.


  • 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-38443: The --enable-universalsdk and --with-universal-archs options for the configure script now check that the specified architectures can be used.

  • bpo-41471: Ignore invalid prefix lengths in system proxy excludes.

  • bpo-41557: Update macOS installer to use SQLite 3.33.0.


  • 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-33987: Mostly finish using ttk widgets, mainly for editor, settings, and searches. Some patches by Mark Roseman.

  • 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-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-42015: Fix potential crash in deallocating method objects when dynamically allocated PyMethodDef's lifetime is managed through the self argument of a PyCFunction.

  • bpo-41986: Py_FileSystemDefaultEncodeErrors and Py_UTF8Mode are available again in limited API.

Python 3.9.0 final

Release date: 2020-10-04


  • bpo-41815: Fix SQLite3 segfault when backing up closed database. Patch contributed by Peter David McCormick.

  • bpo-41662: No longer override exceptions raised in __len__() of a sequence of parameters in sqlite3 with ProgrammingError.

  • bpo-41662: Fixed crash when mutate list of parameters during iteration in sqlite3.

  • bpo-39728: fix default _missing_ so a duplicate ValueError is not set as the __context__ of the original ValueError


  • bpo-41602: Add tests for SIGINT handling in the runpy module.


  • bpo-38249: Update Py_UNREACHABLE to use __builtin_unreachable() if only the compiler is able to use it. Patch by Dong-hee Na.

Python 3.9.0 release candidate 2

Release date: 2020-09-16

Core and Builtins

  • bpo-41780: Fix __dir__() of types.GenericAlias. Patch by Batuhan Taskaya.

  • bpo-41690: Fix a possible stack overflow in the parser when parsing functions and classes with a huge ammount of arguments. Patch by Pablo Galindo.

  • bpo-41681: Fixes the wrong error description in the error raised by using 2 , in format string in f-string and str.format().

  • bpo-41654: Fix a crash that occurred when destroying subclasses of MemoryError. Patch by Pablo Galindo.

  • 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-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-29590: Make the stack trace correct after calling generator.throw() on a generator that has yielded from a yield from.


  • 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-41789: Honor object overrides in Enum class creation (specifically, __str__, __repr__, __format__, and __reduce_ex__).

  • 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-41720: Fixed turtle.Vec2D.__rmul__() for arguments which are not int or float.

  • bpo-41696: Fix handling of debug mode in asyncio.run(). This allows setting PYTHONASYNCIODEBUG or -X dev to enable asyncio debug mode when using asyncio.run().

  • bpo-41687: Fix implementation of sendfile to be compatible with Solaris.

  • bpo-39010: Restarting a ProactorEventLoop on Windows no longer logs spurious ConnectionResetErrors.

  • bpo-41609: The pdb whatis command correctly reports instance methods as 'Method' rather than 'Function'.

  • 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-41503: Fixed a race between setTarget and flush in logging.handlers.MemoryHandler.

  • bpo-41344: Prevent creating shared_memory.SharedMemory objects with size=0.

  • bpo-41025: Fixed an issue preventing the C implementation of zoneinfo.ZoneInfo from being subclassed.

  • bpo-31122: ssl.wrap_socket() now raises ssl.SSLEOFError rather than OSError when peer closes connection during TLS negotiation

  • bpo-33660: Fix pathlib.PosixPath to resolve a relative path located on the root directory properly.


  • bpo-37149: Change Shipman tkinter doc link from archive.org to TkDocs. (The doc has been removed from the NMT server.) The new link responds much faster and includes a short explanatory note.

  • 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-40979: Refactored typing.rst, arranging more than 70 classes, functions, and decorators into new sub-sections.

  • 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-41731: Make test_cmd_line_script pass with option '-vv'.


  • bpo-41617: Fix pycore_byteswap.h header file to support old clang versions: __builtin_bswap16() is not available in LLVM clang 3.0.


  • bpo-41526: Fixed layout of final page of the installer by removing the special thanks to Mark Hammond (with his permission).


  • bpo-41524: Fix bug in PyOS_mystrnicmp and PyOS_mystricmp that incremented pointers beyond the end of a string.

Python 3.9.0 release candidate 1

Release date: 2020-08-11

Core and Builtins

  • bpo-38156: Handle interrupts that come after EOF correctly in PyOS_StdioReadline.



  • 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-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-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.

Python 3.9.0 beta 5

Release date: 2020-07-20


  • 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-39603: Prevent http header injection by rejecting control characters in http.client.putrequest(...).

Core and Builtins

  • 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-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-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-41175: Guard against a NULL pointer dereference within bytearrayobject triggered by the bytearray() + bytearray() operation.

  • 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-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-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-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-39384: Fixed email.contentmanager to allow set_content() to set a null string.


  • bpo-37703: Updated Documentation to comprehensively elaborate on the behaviour of gather.cancel()


  • bpo-40741: Update macOS installer to use SQLite 3.32.3.


  • 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.


Python 3.9.0 beta 4

Release date: 2020-07-02


  • 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).

Core and Builtins

  • bpo-41094: Fix decoding errors with audit when open files with non-ASCII names on non-UTF-8 locale.

  • bpo-41084: Prefix the error message with 'f-string: ', when parsing an f-string expression which throws a SyntaxError.

  • 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-40939: Deprecate PyNode_Compile().

  • 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: Deprecate PyParser_SimpleParseStringFlags(), PyParser_SimpleParseStringFlagsFilename() and PyParser_SimpleParseFileFlags().

  • 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-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-40957: Fix refleak in _Py_fopen_obj() when PySys_Audit() fails

  • bpo-40947: The Python Path Configuration now takes PyConfig.platlibdir in account.

  • 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-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-19569: Add the private macros _Py_COMP_DIAG_PUSH, _Py_COMP_DIAG_IGNORE_DEPR_DECLS, and _Py_COMP_DIAG_POP.


  • 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-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-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: 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-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-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-40924: Removed support for loaders implementing .files and supplying TraversableResources.

  • bpo-40939: Use the new PEG parser when generating the stdlib keyword module.

  • bpo-40834: Fix truncate when sending str object with_xxsubinterpreters.channel_send.

  • 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-38488: Update ensurepip to install pip 20.1.1 and setuptools 47.1.0.

  • bpo-36543: Restored the deprecated xml.etree.cElementTree module.

  • bpo-34226: Fix cgi.parse_multipart without content_length. Patch by Roger Duran


  • bpo-41085: Fix integer overflow in the array.array.index() method on 64-bit Windows for index larger than 2**31.

  • bpo-41069: test.support.TESTFN 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 test.support 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 cyrus.andrew.cmu.edu 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-34401: Make test_gdb properly run on HP-UX. Patch by Michael Osipov.


  • bpo-40204: Pin Sphinx version to 2.3.1 in Doc/Makefile.



  • 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-41005: fixed an XDG settings issue not allowing macos to open browser in webbrowser.py


  • 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-36346: Mark Py_UNICODE_COPY, Py_UNICODE_FILL, PyUnicode_WSTR_LENGTH, PyUnicode_FromUnicode, PyUnicode_AsUnicode, _PyUnicode_AsUnicode, and PyUnicode_AsUnicodeAndSize as deprecated in C. Remove Py_UNICODE_MATCH which was deprecated and broken since Python 3.3.

  • bpo-36020: On Windows, #include "pyerrors.h" no longer defines snprintf and vsnprintf macros.

  • 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".

Python 3.9.0 beta 3

Release date: 2020-06-09


  • bpo-40924: importlib.resources: Reverted TraversableResources implementations from the built-in loaders (SourceFileLoader and ZipImporter) as it was an incompatible change introduced in 3.9.0 beta 2 causing through a chain of events for root TLS certificates to be missing.


  • bpo-40684: make install now uses the PLATLIBDIR variable for the destination lib-dynload/ directory when ./configure --with-platlibdir is used.

Python 3.9.0 beta 2

Release date: 2020-06-08

Core and Builtins

  • 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-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-40696: Fix a hang that can arise after generator.throw() due to a cycle in the exception context chain.


  • bpo-39791: Refresh importlib.metadata from importlib_metadata 1.6.1.

  • bpo-40807: Stop codeop._maybe_compile, used by code.InteractiveInterpreter (and IDLE). from from emitting each warning three times.

  • bpo-39791: Built-in loaders (SourceFileLoader and ZipImporter) now supply TraversableResources implementations for ResourceReader, and the fallback function has been removed.

  • 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-40777: Initialize PyDateTime_IsoCalendarDateType.tp_base at run-time to avoid errors on some compilers.

  • 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-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-40737: Fix possible reference leak for sqlite3 initialization.

  • 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: func:hashlib.new passed usedforsecurity to OpenSSL EVP constructor _hashlib.new(). 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-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-40630: Added tracemalloc.reset_peak() to set the peak size of traced memory blocks to the current size, to measure the peak of specific pieces of code.

  • bpo-13097: ctypes now raises an ArgumentError when a callback is invoked with more than 1024 arguments.

  • bpo-23082: Updated the error message and docs of PurePath.relative_to() to better reflect the function behaviour.

  • 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-35714: struct.error is now raised if there is a null character in a struct format string.

  • bpo-36290: AST nodes are now raising TypeError on conflicting keyword arguments. Patch contributed by Rémi Lapeyre.



  • bpo-40514: Remove --with-experimental-isolated-subinterpreters configure option in Python 3.9: the experiment continues in the master branch, but it's no longer needed in 3.9.

  • bpo-40683: Fixed an issue where the zoneinfo module and its tests were not included when Python is installed with make.


  • 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-40741: Update macOS installer to use SQLite 3.32.2.


  • 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-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-40826: PyOS_InterruptOccurred() now fails with a fatal error if it is called with the GIL released.

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 datetime.date 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): https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274

  • 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): https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274

  • 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 SpooledTemporaryFile.seek() 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 KqueueSelector.select 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 数据模型 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 test_c_locale_coercion.py 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 test.support.wait_process() 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: python.org 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 overalocated 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 codecs.open() at parity with io.open(), 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: https://www.w3.org/TR/xml/#sec-prolog-dtd).

  • 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: setup.py 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 nuget.org 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 python-gdb.py to FreeBSD. python-gdb.py 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 unittest.case.shortDescription().

  • 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 news.gmane.org to news.gmane.io 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 os.link() 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 socket.py, codeop.py and dyld.py 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 test.support 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: test.support: run_python_until_end(), assert_python_ok() and assert_python_failure() functions no longer strip whitespaces from stderr. Remove test.support.strip_python_stderr() 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 asyncio.run() 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(), io.open(), codecs.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 script.py"): 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 collections.abc.MutableSet.

  • 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 hmac.new 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 PR 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 collections.abc 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, asyncio.run() 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: inspect.py 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 unittest.mock.call 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 test_statistics.py 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 test.support.bytecode_helper. 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: ensurepip now uses importlib.resources.read_binary() to read data instead of pkgutil.get_data(). Patch by Joannah Nanjekye.

  • bpo-28292: Mark calendar.py helper functions as being private. The follows PEP 8 guidance to maintain the style conventions in the module and it addresses a known case of user confusion.

  • bpo-18049: Add definition of THREAD_STACK_SIZE for AIX in Python/thread_pthread.h The default thread stacksize caused crashes with the default recursion limit Patch by M Felt

  • bpo-37742: The logging.getLogger() API now returns the root logger when passed the name 'root', whereas previously it returned a non-root logger named 'root'. This could affect cases where user code explicitly wants a non-root logger named 'root', or instantiates a logger using logging.getLogger(__name__) in some top-level module called 'root.py'.

  • bpo-37738: Fix the implementation of curses addch(str, color_pair): pass the color pair to setcchar(), instead of always passing 0 as the color pair.

  • bpo-37723: Fix performance regression on regular expression parsing with huge character sets. Patch by Yann Vaginay.

  • bpo-35943: The function PyImport_GetModule() now ensures any module it returns is fully initialized. Patch by Joannah Nanjekye.

  • bpo-32178: Fix IndexError in email package when trying to parse invalid address fields starting with :.

  • bpo-37268: The parser module is deprecated and will be removed in future versions of Python.

  • bpo-11953: Completing WSA* error codes in socket.

  • bpo-37685: Fixed comparisons of datetime.timedelta and datetime.timezone.

  • bpo-37697: Synchronize importlib.metadata with importlib_metadata 0.19, improving handling of EGG-INFO files and fixing a crash when entry point names contained colons.

  • bpo-37695: Correct curses.unget_wch() error message. Patch by Anthony Sottile.

  • bpo-37689: Add is_relative_to() in PurePath to determine whether or not one path is relative to another.

  • bpo-29553: Fixed argparse.ArgumentParser.format_usage() for mutually exclusive groups. Patch by Andrew Nester.

  • bpo-37691: Let math.dist() accept coordinates as sequences (or iterables) rather than just tuples.

  • bpo-37685: Fixed __eq__, __lt__ etc implementations in some classes. They now return NotImplemented for unsupported type of the other operand. This allows the other operand to play role (for example the equality comparison with ANY will return True).

  • bpo-37354: Make Activate.ps1 Powershell script static to allow for signing it.

  • bpo-37664: Update wheels bundled with ensurepip (pip 19.2.3 and setuptools 41.2.0)

  • bpo-37663: Bring consistency to venv shell activation scripts by always using __VENV_PROMPT__.

  • bpo-37642: Allowed the pure Python implementation of datetime.timezone to represent sub-minute offsets close to minimum and maximum boundaries, specifically in the ranges (23:59, 24:00) and (-23:59, 24:00). Patch by Ngalim Siregar

  • bpo-36161: In posix, use ttyname_r instead of ttyname for thread safety.

  • bpo-36324: Make internal attributes for statistics.NormalDist() private.

  • bpo-37555: Fix NonCallableMock._call_matcher returning tuple instead of _Call object when self._spec_signature exists. Patch by Elizabeth Uselton

  • bpo-29446: Make from tkinter import * import only the expected objects.

  • bpo-16970: Adding a value error when an invalid value in passed to nargs Patch by Robert Leenders

  • bpo-34443: Exceptions from enum now use the __qualname of the enum class in the exception message instead of the __name__.

  • bpo-37491: Fix IndexError when parsing email headers with unexpectedly ending bare-quoted string value. Patch by Abhilash Raj.

  • bpo-37587: Make json.loads faster for long strings. (Patch by Marco Paolini)

  • bpo-18378: Recognize "UTF-8" as a valid value for LC_CTYPE in locale._parse_localename.

  • bpo-37579: Return NotImplemented in Python implementation of __eq__ for timedelta and time when the other object being compared is not of the same type to match C implementation. Patch by Karthikeyan Singaravelan.

  • bpo-21478: Record calls to parent when autospecced object is attached to a mock using unittest.mock.attach_mock(). Patch by Karthikeyan Singaravelan.

  • bpo-37531: "python3 -m test -jN --timeout=TIMEOUT" now kills a worker process if it runs longer than TIMEOUT seconds.

  • bpo-37482: Fix serialization of display name in originator or destination address fields with both encoded words and special chars.

  • bpo-36993: Improve error reporting for corrupt zip files with bad zip64 extra data. Patch by Daniel Hillier.

  • bpo-37502: pickle.loads() no longer raises TypeError when the buffers argument is set to None

  • bpo-37520: Correct behavior for zipfile.Path.parent when the path object identifies a subdirectory.

  • bpo-18374: Fix the .col_offset attribute of nested ast.BinOp instances which had a too large value in some situations.

  • bpo-37424: Fixes a possible hang when using a timeout on subprocess.run() while capturing output. If the child process spawned its own children or otherwise connected its stdout or stderr handles with another process, we could hang after the timeout was reached and our child was killed when attempting to read final output from the pipes.

  • bpo-37421: Fix multiprocessing.util.get_temp_dir() finalizer: clear also the 'tempdir' configuration of the current process, so next call to get_temp_dir() will create a new temporary directory, rather than reusing the removed temporary directory.

  • bpo-37481: The distutils bdist_wininst command is deprecated in Python 3.8, use bdist_wheel (wheel packages) instead.

  • bpo-37479: When Enum.__str__ is overridden in a derived class, the override will be used by Enum.__format__ regardless of whether mixin classes are present.

  • bpo-37440: http.client now enables TLS 1.3 post-handshake authentication for default context or if a cert_file is passed to HTTPSConnection.

  • bpo-37437: Update vendorized expat version to 2.2.7.

  • bpo-37428: SSLContext.post_handshake_auth = True no longer sets SSL_VERIFY_POST_HANDSHAKE verify flag for client connections. Although the option is documented as ignored for clients, OpenSSL implicitly enables cert chain validation when the flag is set.

  • bpo-37420: os.sched_setaffinity() now correctly handles errors that arise during iteration over its mask argument. Patch by Brandt Bucher.

  • bpo-37412: The os.getcwdb() function now uses the UTF-8 encoding on Windows, rather than the ANSI code page: see PEP 529 for the rationale. The function is no longer deprecated on Windows.

  • bpo-37406: The sqlite3 module now raises TypeError, rather than ValueError, if operation argument type is not str: execute(), executemany() and calling a connection.

  • bpo-29412: Fix IndexError in parsing a header value ending unexpectedly. Patch by Abhilash Raj.

  • bpo-36546: The dist argument for statistics.quantiles() is now positional only. The current name doesn't reflect that the argument can be either a dataset or a distribution. Marking the parameter as positional avoids confusion and makes it possible to change the name later.

  • bpo-37394: Fix a bug that was causing the queue module to fail if the accelerator module was not available. Patch by Pablo Galindo.

  • bpo-37376: pprint now has support for types.SimpleNamespace. Patch by Carl Bordum Hansen.

  • bpo-26967: An ArgumentParser with allow_abbrev=False no longer disables grouping of short flags, such as -vv, but only disables abbreviation of long flags as documented. Patch by Zac Hatfield-Dodds.

  • bpo-37212: unittest.mock.call() now preserves the order of keyword arguments in repr output. Patch by Karthikeyan Singaravelan.

  • bpo-37372: Fix error unpickling datetime.time objects from Python 2 with seconds>=24. Patch by Justin Blanchard.

  • bpo-37345: Add formal support for UDPLITE sockets. Support was present before, but it is now easier to detect support with hasattr(socket, 'IPPROTO_UDPLITE') and there are constants defined for each of the values needed: socket.IPPROTO_UDPLITE, UDPLITE_SEND_CSCOV, and UDPLITE_RECV_CSCOV. Patch by Gabe Appleton.

  • bpo-37358: Optimized functools.partial by using vectorcall.

  • bpo-37347: sqlite3.Connection.create_aggregate(), sqlite3.Connection.create_function(), sqlite3.Connection.set_authorizer(), sqlite3.Connection.set_progress_handler() sqlite3.Connection.set_trace_callback() methods lead to segfaults if some of these methods are called twice with an equal object but not the same. Now callbacks are stored more carefully. Patch by Aleksandr Balezin.

  • bpo-37163: The obj argument of dataclasses.replace() is positional-only now.

  • bpo-37085: Add the optional Linux SocketCAN Broadcast Manager constants, used as flags to configure the BCM behaviour, in the socket module. Patch by Karl Ding.

  • bpo-37328: HTMLParser.unescape is removed. It was undocumented and deprecated since Python 3.4.

  • bpo-37305: Add .webmanifest -> application/manifest+json to list of recognized file types and content type headers

  • bpo-37320: aifc.openfp() alias to aifc.open(), sunau.openfp() alias to sunau.open(), and wave.openfp() alias to wave.open() have been removed. They were deprecated since Python 3.7.

  • bpo-37315: Deprecated accepting floats with integral value (like 5.0) in math.factorial().

  • bpo-37312: _dummy_thread and dummy_threading modules have been removed. These modules were deprecated since Python 3.7 which requires threading support.

  • bpo-33972: Email with single part but content-type set to multipart/* doesn't raise AttributeError anymore.

  • bpo-37280: Use threadpool for reading from file for sendfile fallback mode.

  • bpo-37279: Fix asyncio sendfile support when sendfile sends extra data in fallback mode.

  • bpo-19865: ctypes.create_unicode_buffer() now also supports non-BMP characters on platforms with 16-bit wchar_t (for example, Windows and AIX).

  • bpo-37266: In a subinterpreter, spawning a daemon thread now raises an exception. Daemon threads were never supported in subinterpreters. Previously, the subinterpreter finalization crashed with a Python fatal error if a daemon thread was still running.

  • bpo-37210: Allow pure Python implementation of pickle to work even when the C _pickle module is unavailable.

  • bpo-21872: Fix lzma: module decompresses data incompletely. When decompressing a FORMAT_ALONE format file, and it doesn't have the end marker, sometimes the last one to dozens bytes can't be output. Patch by Ma Lin.

  • bpo-35922: Fix RobotFileParser.crawl_delay() and RobotFileParser.request_rate() to return None rather than raise AttributeError when no relevant rule is defined in the robots.txt file. Patch by Rémi Lapeyre.

  • bpo-35766: Change the format of feature_version to be a (major, minor) tuple.

  • bpo-36607: Eliminate RuntimeError raised by asyncio.all_tasks() if internal tasks weak set is changed by another thread during iteration.

  • bpo-18748: _pyio.IOBase destructor now does nothing if getting the closed attribute fails to better mimic _io.IOBase finalizer.

  • bpo-36402: Fix a race condition at Python shutdown when waiting for threads. Wait until the Python thread state of all non-daemon threads get deleted (join all non-daemon threads), rather than just wait until non-daemon Python threads complete.

  • bpo-37206: Default values which cannot be represented as Python objects no longer improperly represented as None in function signatures.

  • bpo-37111: Added encoding and errors keyword parameters to logging.basicConfig.

  • bpo-12144: Ensure cookies with expires attribute are handled in CookieJar.make_cookies().

  • bpo-34886: Fix an unintended ValueError from subprocess.run() when checking for conflicting input and stdin or capture_output and stdout or stderr args when they were explicitly provided but with None values within a passed in **kwargs dict rather than as passed directly by name. Patch contributed by Rémi Lapeyre.

  • bpo-37173: The exception message for inspect.getfile() now correctly reports the passed class rather than the builtins module.

  • bpo-37178: Give math.perm() a one argument form that means the same as math.factorial().

  • bpo-37178: For math.perm(n, k), let k default to n, giving the same result as factorial.

  • bpo-37165: Converted _collections._count_elements to use the Argument Clinic.

  • bpo-34767: Do not always create a collections.deque in asyncio.Lock.

  • bpo-37158: Speed-up statistics.fmean() by switching from a function to a generator.

  • bpo-34282: Remove Enum._convert method, deprecated in 3.8.

  • bpo-37150: argparse._ActionsContainer.add_argument now throws error, if someone accidentally pass FileType class object instead of instance of FileType as type argument

  • bpo-28724: The socket module now has the socket.send_fds() and socket.recv.fds() methods. Contributed by Joannah Nanjekye, Shinya Okano and Victor Stinner.

  • bpo-35621: Support running asyncio subprocesses when execution event loop in a thread on UNIX.

  • bpo-36520: Lengthy email headers with UTF-8 characters are now properly encoded when they are folded. Patch by Jeffrey Kintscher.

  • bpo-30835: Fixed a bug in email parsing where a message with invalid bytes in content-transfer-encoding of a multipart message can cause an AttributeError. Patch by Andrew Donnellan.

  • bpo-31163: pathlib.Path instance's rename and replace methods now return the new Path instance.

  • bpo-25068: urllib.request.ProxyHandler now lowercases the keys of the passed dictionary.

  • bpo-26185: Fix repr() on empty ZipInfo object. Patch by Mickaël Schoentgen.

  • bpo-21315: Email headers containing RFC2047 encoded words are parsed despite the missing whitespace, and a defect registered. Also missing trailing whitespace after encoded words is now registered as a defect.

  • bpo-31904: Port test_datetime to VxWorks: skip zoneinfo tests on VxWorks

  • bpo-35805: Add parser for Message-ID header and add it to default HeaderRegistry. This should prevent folding of Message-ID using RFC 2048 encoded words.

  • bpo-36871: Ensure method signature is used instead of constructor signature of a class while asserting mock object against method calls. Patch by Karthikeyan Singaravelan.

  • bpo-35070: posix.getgrouplist() now works correctly when the user belongs to NGROUPS_MAX supplemental groups. Patch by Jeffrey Kintscher.

  • bpo-31783: Fix race condition in ThreadPoolExecutor when worker threads are created during interpreter shutdown.

  • bpo-36582: Fix UserString.encode() to correctly return bytes rather than a UserString instance.

  • bpo-32424: Deprecate xml.etree.ElementTree.Element.copy() in favor of copy.copy().

    Patch by Gordon P. Hemsley

  • bpo-36564: Fix infinite loop in email header folding logic that would be triggered when an email policy's max_line_length is not long enough to include the required markup and any values in the message. Patch by Paul Ganssle

  • bpo-36543: Removed methods Element.getchildren(), Element.getiterator() and ElementTree.getiterator() and the xml.etree.cElementTree module.

  • bpo-36409: Remove the old plistlib API deprecated in Python 3.4

  • bpo-36302: distutils sorts source file lists so that Extension .so files build more reproducibly by default

  • bpo-36250: Ignore ValueError from signal with interaction in non-main thread.

  • bpo-36046: Added user, group and extra_groups parameters to the subprocess.Popen constructor. Patch by Patrick McLean.

  • bpo-32627: Fix compile error when _uuid headers conflicting included.

  • bpo-35800: Deprecate smtpd.MailmanProxy ready for future removal.

  • bpo-35168: shlex.shlex.punctuation_chars is now a read-only property.

  • bpo-8538: Add support for boolean actions like --foo and --no-foo to argparse. Patch contributed by Rémi Lapeyre.

  • bpo-20504: Fixes a bug in cgi module when a multipart/form-data request has no Content-Length header.

  • bpo-25988: The abstract base classes in collections.abc no longer are exposed in the regular collections module.

  • bpo-11122: Distutils won't check for rpmbuild in specified paths only.

  • bpo-34775: Division handling of PurePath now returns NotImplemented instead of raising a TypeError when passed something other than an instance of str or PurePath. Patch by Roger Aiudi.

  • bpo-34749: binascii.a2b_base64() is now up to 2 times faster. Patch by Sergey Fedoseev.

  • bpo-34519: Add additional aliases for HP Roman 8. Patch by Michael Osipov.

  • bpo-28009: Fix uuid.getnode() on platforms with '.' as MAC Addr delimiter as well fix for MAC Addr format that omits a leading 0 in MAC Addr values. Currently, AIX is the only know platform with these settings. Patch by Michael Felt.

  • bpo-30618: Add readlink(). Patch by Girts Folkmanis.

  • bpo-32498: Made urllib.parse.unquote() accept bytes in addition to strings. Patch by Stein Karlsen.

  • bpo-33348: lib2to3 now recognizes expressions after * and ** like in f(*[] or []).

  • bpo-32689: Update shutil.move() function to allow for Path objects to be used as source argument. Patch by Emily Morehouse and Maxwell "5.13b" McKinnon.

  • bpo-32820: Added __format__ to IPv4 and IPv6 classes. Always outputs a fully zero- padded string. Supports b/x/n modifiers (bin/hex/native format). Native format for IPv4 is bin, native format for IPv6 is hex. Also supports '#' and '_' modifiers.

  • bpo-27657: Fix urllib.parse.urlparse() with numeric paths. A string like "path:80" is no longer parsed as a path but as a scheme ("path") and a path ("80").

  • bpo-4963: Fixed non-deterministic behavior related to mimetypes extension mapping and module reinitialization.


  • bpo-21767: Explicitly mention abc support in functools.singledispatch

  • bpo-38816: Provides more details about the interaction between fork() and CPython's runtime, focusing just on the C-API. This includes cautions about where fork() should and shouldn't be called.

  • bpo-38351: Modernize email examples from %-formatting to f-strings.

  • bpo-38778: Document the fact that RuntimeError is raised if os.fork() is called in a subinterpreter.

  • bpo-38592: Add Brazilian Portuguese to the language switcher at Python Documentation website.

  • bpo-38294: Add list of no-longer-escaped chars to re.escape documentation

  • bpo-38053: Modernized the plistlib documentation

  • bpo-26868: Fix example usage of PyModule_AddObject() to properly handle errors.

  • bpo-36797: Fix a dead link in the distutils API Reference.

  • bpo-37977: Warn more strongly and clearly about pickle insecurity

  • bpo-37979: Added a link to dateutil.parser.isoparse in the datetime.fromisoformat documentation. Patch by Paul Ganssle

  • bpo-12707: Deprecate info(), geturl(), getcode() methods in favor of the headers, url, and status properties, respectively, for HTTPResponse and addinfourl. Also deprecate the code attribute of addinfourl in favor of the status attribute. Patch by Ashwin Ramaswami

  • bpo-37937: Mention frame.f_trace in sys.settrace() docs.

  • bpo-37878: Make PyThreadState_DeleteCurrent() Internal.

  • bpo-37759: Beginning edits to Whatsnew 3.8

  • bpo-37726: Stop recommending getopt in the tutorial for command line argument parsing and promote argparse.

  • bpo-32910: Remove implementation-specific behaviour of how venv's Deactivate works.

  • bpo-37256: Fix wording of arguments for Request in urllib.request

  • bpo-37284: Add a brief note to indicate that any new sys.implementation required attributes must go through the PEP process.

  • bpo-30088: Documented that mailbox.Maildir constructor doesn't attempt to verify the maildir folder layout correctness. Patch by Sviatoslav Sydorenko.

  • bpo-37521: Fix importlib examples to insert any newly created modules via importlib.util.module_from_spec() immediately into sys.modules instead of after calling loader.exec_module().

    Thanks to Benjamin Mintz for finding the bug.

  • bpo-37456: Slash ('/') is now part of syntax.

  • bpo-37487: Fix PyList_GetItem index description to include 0.

  • bpo-37149: Replace the dead link to the Tkinter 8.5 reference by John Shipman, New Mexico Tech, with a link to the archive.org copy.

  • bpo-37478: Added possible exceptions to the description of os.chdir().

  • bpo-34903: Documented that in datetime.datetime.strptime(), the leading zero in some two-digit formats is optional. Patch by Mike Gleen.

  • bpo-36260: Add decompression pitfalls to zipfile module documentation.

  • bpo-37004: In the documentation for difflib, a note was added explicitly warning that the results of SequenceMatcher's ratio method may depend on the order of the input strings.

  • bpo-36960: Restructured the datetime docs in the interest of making them more user-friendly and improving readability. Patch by Brad Solomon.

  • bpo-36487: Make C-API docs clear about what the "main" interpreter is.

  • bpo-23460: The documentation for decimal string formatting using the :g specifier has been updated to reflect the correct exponential notation cutoff point. Original patch contributed by Tuomas Suutari.

  • bpo-35803: Document and test that tempfile functions may accept a path-like object for the dir argument. Patch by Anthony Sottile.

  • bpo-33944: Added a note about the intended use of code in .pth files.

  • bpo-34293: Fix the Doc/Makefile regarding PAPER environment variable and PDF builds

  • bpo-25237: Add documentation for tkinter modules


  • bpo-38614: Fix test_communicate() of test_asyncio.test_subprocess: use support.LONG_TIMEOUT (5 minutes), instead of just 1 minute.

  • bpo-38614: Add timeout constants to test.support: LOOPBACK_TIMEOUT, INTERNET_TIMEOUT, SHORT_TIMEOUT and LONG_TIMEOUT.

  • bpo-38502: test.regrtest now uses process groups in the multiprocessing mode (-jN command line option) if process groups are available: if os.setsid() and os.killpg() functions are available.

  • bpo-35998: Fix a race condition in test_asyncio.test_start_tls_server_1(). Previously, there was a race condition between the test main() function which replaces the protocol and the test ServerProto protocol which sends ANSWER once it gets HELLO. Now, only the test main() function is responsible to send data, ServerProto no longer sends data.

  • bpo-38470: Fix test_compileall.test_compile_dir_maxlevels() on Windows without long path support: only create 3 subdirectories instead of between 20 and 100 subdirectories.

  • bpo-37531: On timeout, regrtest no longer attempts to call popen.communicate() again: it can hang until all child processes using stdout and stderr pipes completes. Kill the worker process and ignores its output. Change also the faulthandler timeout of the main process from 1 minute to 5 minutes, for Python slowest buildbots.

  • bpo-38239: Fix test_gdb for Link Time Optimization (LTO) builds.

  • bpo-38275: test_ssl now handles disabled TLS/SSL versions better. OpenSSL's crypto policy and run-time settings are recognized and tests for disabled versions are skipped. Tests also accept more TLS minimum_versions for platforms that override OpenSSL's default with strict settings.

  • bpo-38271: The private keys for test_ssl were encrypted with 3DES in traditional PKCS#5 format. 3DES and the digest algorithm of PKCS#5 are blocked by some strict crypto policies. Use PKCS#8 format with AES256 encryption instead.

  • bpo-38270: test.support now has a helper function to check for availability of a hash digest function. Several tests are refactored avoid MD5 and use SHA256 instead. Other tests are marked to use MD5 and skipped when MD5 is disabled.

  • bpo-37123: Multiprocessing test test_mymanager() now also expects -SIGTERM, not only exitcode 0. BaseManager._finalize_manager() sends SIGTERM to the manager process if it takes longer than 1 second to stop, which happens on slow buildbots.

  • bpo-38212: Multiprocessing tests: increase test_queue_feeder_donot_stop_onexc() timeout from 1 to 60 seconds.

  • bpo-38117: Test with OpenSSL 1.1.1d

  • bpo-38018: Increase code coverage for multiprocessing.shared_memory.

  • bpo-37805: Add tests for json.dump(..., skipkeys=True). Patch by Dong-hee Na.

  • bpo-37531: Enhance regrtest multiprocess timeout: write a message when killing a worker process, catch popen.kill() and popen.wait() exceptions, put a timeout on the second call to popen.communicate().

  • bpo-37876: Add tests for ROT-13 codec.

  • bpo-36833: Added tests for PyDateTime_xxx_GET_xxx() macros of the C API of the datetime module. Patch by Joannah Nanjekye.

  • bpo-37558: Fix test_shared_memory_cleaned_after_process_termination name handling

  • bpo-37526: Add test.support.catch_threading_exception(): context manager catching threading.Thread exception using threading.excepthook().

  • bpo-37421: test_concurrent_futures now explicitly stops the ForkServer instance if it's running.

  • bpo-37421: multiprocessing tests now stop the ForkServer instance if it's running: close the "alive" file descriptor to ask the server to stop and then remove its UNIX address.

  • bpo-37421: test_distutils.test_build_ext() is now able to remove the temporary directory on Windows: don't import the newly built C extension ("xx") in the current process, but test it in a separated process.

  • bpo-37421: test_concurrent_futures now cleans up multiprocessing to remove immediately temporary directories created by multiprocessing.util.get_temp_dir().

  • bpo-37421: test_winconsoleio doesn't leak a temporary file anymore: use tempfile.TemporaryFile() to remove it when the test completes.

  • bpo-37421: multiprocessing tests now explicitly call _run_finalizers() to immediately remove temporary directories created by tests.

  • bpo-37421: urllib.request tests now call urlcleanup() to remove temporary files created by urlretrieve() tests and to clear the _opener global variable set by urlopen() and functions calling indirectly urlopen().

  • bpo-37472: Remove Lib/test/outstanding_bugs.py.

  • bpo-37199: Fix test failures when IPv6 is unavailable or disabled.

  • bpo-19696: Replace deprecated method "random.choose" with "random.choice" in "test_pkg_import.py".

  • bpo-37335: Remove no longer necessary code from c locale coercion tests

  • bpo-37421: Fix test_shutil to no longer leak temporary files.

  • bpo-37411: Fix test_wsgiref.testEnviron() to no longer depend on the environment variables (don't fail if "X" variable is set).

  • bpo-37400: Fix test_os.test_chown(): use os.getgroups() rather than grp.getgrall() to get groups. Rename also the test to test_chown_gid().

  • bpo-37359: Add --cleanup option to python3 -m test to remove test_python_* directories of previous failed jobs. Add "make cleantest" to run python3 -m test --cleanup.

  • bpo-37362: test_gdb no longer fails if it gets an "unexpected" message on stderr: it now ignores stderr. The purpose of test_gdb is to test that python-gdb.py commands work as expected, not to test gdb.

  • bpo-35998: Avoid TimeoutError in test_asyncio: test_start_tls_server_1()

  • bpo-37278: Fix test_asyncio ProactorLoopCtrlC: join the thread to prevent leaking a running thread and leaking a reference.

  • bpo-37261: Fix test.support.catch_unraisable_exception(): its __exit__() method now ignores unraisable exception raised when clearing its unraisable attribute.

  • bpo-37069: regrtest now uses sys.unraisablehook() to mark a test as "environment altered" (ENV_CHANGED) if it emits an "unraisable exception". Moreover, regrtest logs a warning in this case.

    Use python3 -m test --fail-env-changed to catch unraisable exceptions in tests.

  • bpo-37252: Fix assertions in test_close and test_events_mask_overflow devpoll tests.

  • bpo-37169: Rewrite _PyObject_IsFreed() unit tests.

  • bpo-37153: test_venv.test_multiprocessing() now explicitly calls pool.terminate() to wait until the pool completes.

  • bpo-34001: Make test_ssl pass with LibreSSL. LibreSSL handles minimum and maximum TLS version differently than OpenSSL.

  • bpo-36919: Make test_source_encoding.test_issue2301 implementation independent. The test will work now for both CPython and IronPython.

  • bpo-30202: Update test.test_importlib.test_abc to test find_spec().

  • bpo-28009: Modify the test_uuid logic to test when a program is available AND can be used to obtain a MACADDR as basis for an UUID. Patch by M. Felt

  • bpo-34596: Fallback to a default reason when unittest.skip() is uncalled. Patch by Naitree Zhu.


  • bpo-38809: On Windows, build scripts will now recognize and use python.exe from an active virtual env.

  • bpo-38684: Fix _hashlib build when Blake2 is disabled, but OpenSSL supports it.

  • bpo-38468: Misc/python-config.in now uses getvar() for all still existing sysconfig.get_config_var() calls. Patch by Joannah Nanjekye.

  • bpo-37415: Fix stdatomic.h header check for ICC compiler: the ICC implementation lacks atomic_uintptr_t type which is needed by Python.

  • bpo-38301: In Solaris family, we must be sure to use -D_REENTRANT. Patch by Jesús Cea Avión.

  • bpo-36002: Locate llvm-profdata and llvm-ar binaries using AC_PATH_TOOL rather than AC_PATH_TARGET_TOOL.

  • bpo-37936: The .gitignore file systematically keeps "rooted", with a non-trailing slash, all the rules that are meant to apply to files in a specific place in the repo. Previously, when the intended file to ignore happened to be at the root of the repo, we'd most often accidentally also ignore files and directories with the same name anywhere in the tree.

  • bpo-37760: The Tools/unicode/makeunicodedata.py script, which is used for converting information from the Unicode Character Database into generated code and data used by the methods of str and by the unicodedata module, now handles each character's data as a dataclass with named attributes, rather than a length-18 list of different fields.

  • bpo-37936: The .gitignore file no longer applies to any files that are in fact tracked in the Git repository. Patch by Greg Price.

  • bpo-37725: Change "clean" makefile target to also clean the program guided optimization (PGO) data. Previously you would have to use "make clean" and "make profile-removal", or "make clobber".

  • bpo-37707: Mark some individual tests to skip when --pgo is used. The tests marked increase the PGO task time significantly and likely don't help improve optimization of the final executable.

  • bpo-36044: Reduce the number of unit tests run for the PGO generation task. This speeds up the task by a factor of about 15x. Running the full unit test suite is slow. This change may result in a slightly less optimized build since not as many code branches will be executed. If you are willing to wait for the much slower build, the old behavior can be restored using './configure [..] PROFILE_TASK="-m test --pgo-extended"'. We make no guarantees as to which PGO task set produces a faster build. Users who care should run their own relevant benchmarks as results can depend on the environment, workload, and compiler tool chain.

  • bpo-37468: make install no longer installs wininst-*.exe files used by distutils bdist_wininst: bdist_wininst only works on Windows.

  • bpo-37189: Many PyRun_XXX() functions like PyRun_String() were no longer exported in libpython38.dll by mistake. Export them again to fix the ABI compatibility.

  • bpo-25361: Enables use of SSE2 instructions in Windows 32-bit build.

  • bpo-36210: Update optional extension module detection for AIX. ossaudiodev and spwd are not applicable for AIX, and are no longer reported as missing. 3rd-party packaging of ncurses (with ASIS support) conflicts with officially supported AIX curses library, so configure AIX to use libcurses.a. However, skip trying to build _curses_panel.

    patch by M Felt


  • bpo-38589: Fixes HTML Help shortcut when Windows is not installed to C drive

  • bpo-38453: Ensure ntpath.realpath() correctly resolves relative paths.

  • bpo-38519: Restores the internal C headers that were missing from the nuget.org and Microsoft Store packages.

  • bpo-38492: Remove pythonw.exe dependency on the Microsoft C++ runtime.

  • bpo-38344: Fix error message in activate.bat

  • bpo-38359: Ensures pyw.exe launcher reads correct registry key.

  • bpo-38355: Fixes ntpath.realpath failing on sys.executable.

  • bpo-38117: Update bundled OpenSSL to 1.1.1d

  • bpo-38092: Reduce overhead when using multiprocessing in a Windows virtual environment.

  • bpo-38133: Allow py.exe launcher to locate installations from the Microsoft Store and improve display of active virtual environments.

  • bpo-38114: The pip.ini is no longer included in the Nuget package.

  • bpo-32592: Set Windows 8 as the minimum required version for API support

  • bpo-36634: os.cpu_count() now returns active processors rather than maximum processors.

  • bpo-36634: venv activate.bat now works when the existing variables contain double quote characters.

  • bpo-38081: Prevent error calling os.path.realpath() on 'NUL'.

  • bpo-38087: Fix case sensitivity in test_pathlib and test_ntpath.

  • bpo-38088: Fixes distutils not finding vcruntime140.dll with only the v142 toolset installed.

  • bpo-37283: Ensure command-line and unattend.xml setting override previously detected states in Windows installer.

  • bpo-38030: Fixes os.stat() failing for block devices on Windows

  • bpo-38020: Fixes potential crash when calling os.readlink() (or indirectly through realpath()) on a file that is not a supported link.

  • bpo-37705: Improve the implementation of winerror_to_errno().

  • bpo-37549: os.dup() no longer fails for standard streams on Windows 7.

  • bpo-1311: The nul file on Windows now returns True from exists() and a valid result from os.stat() with S_IFCHR set.

  • bpo-9949: Enable support for following symlinks in os.realpath().

  • bpo-37834: Treat all name surrogate reparse points on Windows in os.lstat() and other reparse points as regular files in os.stat().

  • bpo-36266: Add the module name in the formatted error message when DLL load fail happens during module import in _PyImport_FindSharedFuncptrWindows(). Patch by Srinivas Nyayapati.

  • bpo-25172: Trying to import the crypt module on Windows will result in an ImportError with a message explaining that the module isn't supported on Windows. On other platforms, if the underlying _crypt module is not available, the ImportError will include a message explaining the problem.

  • bpo-37778: Fixes the icons used for file associations to the Microsoft Store package.

  • bpo-37734: Fix use of registry values to launch Python from Microsoft Store app.

  • bpo-37702: Fix memory leak on Windows in creating an SSLContext object or running urllib.request.urlopen('https://...').

  • bpo-37672: Switch Windows Store package's pip to use bundled pip.ini instead of PIP_USER variable.

  • bpo-10945: Officially drop support for creating bdist_wininst installers on non-Windows systems.

  • bpo-37445: Include the FORMAT_MESSAGE_IGNORE_INSERTS flag in FormatMessageW() calls.

  • bpo-37369: Fixes path for sys.executable when running from the Microsoft Store.

  • bpo-37380: Don't collect unfinished processes with subprocess._active on Windows to cleanup later. Patch by Ruslan Kuprieiev.

  • bpo-37351: Removes libpython38.a from standard Windows distribution.

  • bpo-35360: Update Windows builds to use SQLite 3.28.0.

  • bpo-37267: On Windows, os.dup() no longer creates an inheritable fd when handling a character file.

  • bpo-36779: Ensure time.tzname is correct on Windows when the active code page is set to CP_UTF7 or CP_UTF8.

  • bpo-32587: Make winreg.REG_MULTI_SZ support zero-length strings.

  • bpo-28269: Replace use of strcasecmp() for the system function _stricmp(). Patch by Minmin Gong.

  • bpo-36590: Add native Bluetooth RFCOMM support to socket module.


  • bpo-38117: Updated OpenSSL to 1.1.1d in macOS installer.

  • bpo-38089: Move Azure Pipelines to latest VM versions and make macOS tests optional

  • bpo-18049: Increase the default stack size of threads from 5MB to 16MB on macOS, to match the stack size of the main thread. This avoids crashes on deep recursion in threads.

  • bpo-34602: Avoid test suite failures on macOS by no longer calling resource.setrlimit to increase the process stack size limit at runtime. The runtime change is no longer needed since the interpreter is being built with a larger default stack size.

  • bpo-35360: Update macOS installer to use SQLite 3.28.0.

  • bpo-34631: Updated OpenSSL to 1.1.1c in macOS installer.


  • bpo-26353: Stop adding newline when saving an IDLE shell window.

  • bpo-4630: Add an option to toggle IDLE's cursor blink for shell, editor, and output windows. See Settings, General, Window Preferences, Cursor Blink. Patch by Zackery Spytz.

  • bpo-38598: Do not try to compile IDLE shell or output windows

  • bpo-36698: IDLE no longer fails when write non-encodable characters to stderr. It now escapes them with a backslash, as the regular Python interpreter. Added the errors field to the standard streams.

  • bpo-35379: When exiting IDLE, catch any AttributeError. One happens when EditorWindow.close is called twice. Printing a traceback, when IDLE is run from a terminal, is useless and annoying.

  • bpo-38183: To avoid problems, test_idle ignores the user config directory. It no longer tries to create or access .idlerc or any files within. Users must run IDLE to discover problems with saving settings.

  • bpo-38077: IDLE no longer adds 'argv' to the user namespace when initializing it. This bug only affected 3.7.4 and 3.8.0b2 to 3.8.0b4.

  • bpo-38041: Shell restart lines now fill the window width, always start with '=', and avoid wrapping unnecessarily. The line will still wrap if the included file name is long relative to the width.

  • bpo-35771: To avoid occasional spurious test_idle failures on slower machines, increase the hover_delay in test_tooltip.

  • bpo-37824: Properly handle user input warnings in IDLE shell. Cease turning SyntaxWarnings into SyntaxErrors.

  • bpo-37929: IDLE Settings dialog now closes properly when there is no shell window.

  • bpo-37902: Add mousewheel scrolling for IDLE module, path, and stack browsers. Patch by George Zhang.

  • bpo-37849: Fixed completions list appearing too high or low when shown above the current line.

  • bpo-36419: Refactor IDLE autocomplete and improve testing.

  • bpo-37748: Reorder the Run menu. Put the most common choice, Run Module, at the top.

  • bpo-37692: Improve highlight config sample with example shell interaction and better labels for shell elements.

  • bpo-37628: Settings dialog no longer expands with font size.

  • bpo-37627: Initialize the Customize Run dialog with the command line arguments most recently entered before. The user can optionally edit before submitting them.

  • bpo-33610: Fix code context not showing the correct context when first toggled on.

  • bpo-37530: Optimize code context to reduce unneeded background activity. Font and highlight changes now occur along with text changes instead of after a random delay.

  • bpo-27452: Cleanup config.py by inlining RemoveFile and simplifying the handling of file in CreateConfigHandlers.

  • bpo-37325: Fix tab focus traversal order for help source and custom run dialogs.

  • bpo-37321: Both subprocess connection error messages now refer to the 'Startup failure' section of the IDLE doc.

  • bpo-17535: Add optional line numbers for IDLE editor windows. Windows open without line numbers unless set otherwise in the General tab of the configuration dialog.

  • bpo-26806: To compensate for stack frames added by IDLE and avoid possible problems with low recursion limits, add 30 to limits in the user code execution process. Subtract 30 when reporting recursion limits to make this addition mostly transparent.

  • bpo-37177: Properly 'attach' search dialogs to their main window so that they behave like other dialogs and do not get hidden behind their main window.

  • bpo-37039: Adjust "Zoom Height" to individual screens by momentarily maximizing the window on first use with a particular screen. Changing screen settings may invalidate the saved height. While a window is maximized, "Zoom Height" has no effect.

  • bpo-35763: Make calltip reminder about '/' meaning positional-only less obtrusive by only adding it when there is room on the first line.

  • bpo-5680: Add 'Run... Customized' to the Run menu to run a module with customized settings. Any 'command line arguments' entered are added to sys.argv. One can suppress the normal Shell main module restart.

  • bpo-36390: Gather Format menu functions into format.py. Combine paragraph.py, rstrip.py, and format methods from editor.py.


  • bpo-38118: Update Valgrind suppression file to ignore a false alarm in PyUnicode_Decode() when using GCC builtin strcmp().

  • bpo-38347: pathfix.py: Assume all files that end on '.py' are Python scripts when working recursively.

  • bpo-37803: pdb's --help and --version long options now work.

  • bpo-37942: Improve ArgumentClinic converter for floats.

  • bpo-37704: Remove Tools/scripts/h2py.py: use cffi to access a C API in Python.

  • bpo-37675: 2to3 now works when run from a zipped standard library.

  • bpo-37034: Argument Clinic now uses the argument name on errors with keyword-only argument instead of their position. Patch contributed by Rémi Lapeyre.

  • bpo-37064: Add option -k to pathscript.py script: preserve shebang flags. Add option -a to pathscript.py script: add flags.


  • bpo-37633: Re-export some function compatibility wrappers for macros in pythonrun.h.

  • bpo-38644: Provide Py_EnterRecursiveCall() and Py_LeaveRecursiveCall() as regular functions for the limited API. Previously, there were defined as macros, but these macros didn't work with the limited API which cannot access PyThreadState.recursion_depth field. Remove _Py_CheckRecursionLimit from the stable ABI.

  • bpo-38650: The global variable PyStructSequence_UnnamedField is now a constant and refers to a constant string.

  • bpo-38540: Fixed possible leak in PyArg_Parse() and similar functions for format units "es#" and "et#" when the macro PY_SSIZE_T_CLEAN is not defined.

  • bpo-38395: Fix a crash in weakref.proxy objects due to incorrect lifetime management when calling some associated methods that may delete the last reference to object being referenced by the proxy. Patch by Pablo Galindo.

  • bpo-36389: The _PyObject_CheckConsistency() function is now also available in release mode. For example, it can be used to debug a crash in the visit_decref() function of the GC.

  • bpo-38266: Revert the removal of PyThreadState_DeleteCurrent() with documentation.

  • bpo-38303: Update audioop extension module to use the stable ABI (PEP-384). Patch by Tyler Kieft.

  • bpo-38234: Py_SetPath() now sets sys.executable to the program full path (Py_GetProgramFullPath()) rather than to the program name (Py_GetProgramName()).

  • bpo-38234: Python ignored arguments passed to Py_SetPath(), Py_SetPythonHome() and Py_SetProgramName(): fix Python initialization to use specified arguments.

  • bpo-38205: The Py_UNREACHABLE() macro now calls Py_FatalError().

  • bpo-38140: Make dict and weakref offsets opaque for C heap types by passing the offsets through PyMemberDef

  • bpo-15088: The C function PyGen_NeedsFinalizing has been removed. It was not documented, tested or used anywhere within CPython after the implementation of PEP 442. Patch by Joannah Nanjekye. (Patch by Joannah Nanjekye)

  • bpo-36763: Options added by PySys_AddXOption() are now handled the same way than PyConfig.xoptions and command line -X options.

  • bpo-37926: Fix a crash in PySys_SetArgvEx(0, NULL, 0).

  • bpo-37879: Fix subtype_dealloc to suppress the type decref when the base type is a C heap type

  • bpo-37645: Add _PyObject_FunctionStr() to get a user-friendly string representation of a function-like object. Patch by Jeroen Demeyer.

  • bpo-29548: The functions PyEval_CallObject, PyEval_CallFunction, PyEval_CallMethod and PyEval_CallObjectWithKeywords are deprecated. Use PyObject_Call() and its variants instead.

  • bpo-37151: PyCFunction_Call is now a deprecated alias of PyObject_Call().

  • bpo-37540: The vectorcall protocol now requires that the caller passes only strings as keyword names.

  • bpo-37207: The vectorcall protocol is now enabled for type objects: set tp_vectorcall to a vectorcall function to be used instead of tp_new and tp_init when calling the class itself.

  • bpo-21120: Exclude Python-ast.h, ast.h and asdl.h from the limited API.

  • bpo-37483: Add new function _PyObject_CallOneArg for calling an object with one positional argument.

  • bpo-36763: Add PyConfig_SetWideStringList() function.

  • bpo-37337: Add fast functions for calling methods: _PyObject_VectorcallMethod(), _PyObject_CallMethodNoArgs() and _PyObject_CallMethodOneArg().

  • bpo-28805: The METH_FASTCALL calling convention has been documented.

  • bpo-37221: The new function PyCode_NewWithPosOnlyArgs() allows to create code objects like PyCode_New(), but with an extra posonlyargcount parameter for indicating the number of positonal-only arguments.

  • bpo-37215: Fix dtrace issue introduce by bpo-36842

  • bpo-37194: Add a new public PyObject_CallNoArgs() function to the C API: call a callable Python object without any arguments. It is the most efficient way to call a callback without any argument. On x86-64, for example, PyObject_CallFunctionObjArgs(func, NULL) allocates 960 bytes on the stack per call, whereas PyObject_CallNoArgs(func) only allocates 624 bytes per call.

  • bpo-37170: Fix the cast on error in PyLong_AsUnsignedLongLongMask().

  • bpo-35381: Convert posixmodule.c statically allocated types DirEntryType and ScandirIteratorType to heap-allocated types.

  • bpo-34331: Use singular/plural noun in error message when instantiating an abstract class with non-overriden abstract method(s).

Python 3.8.0 beta 1

Release date: 2019-06-04


  • bpo-35907: CVE-2019-9948: Avoid file reading by disallowing local-file:// and local_file:// URL schemes in URLopener().open() and URLopener().retrieve() of urllib.request.

  • bpo-33529: Prevent fold function used in email header encoding from entering infinite loop when there are too many non-ASCII characters in a header.

  • bpo-33164: Updated blake2 implementation which uses secure memset implementation provided by platform.

Core and Builtins

  • bpo-35814: Allow unpacking in the right hand side of annotated assignments. In particular, t: Tuple[int, ...] = x, y, *z is now allowed.

  • bpo-37126: All structseq objects are now tracked by the garbage collector. Patch by Pablo Galindo.

  • bpo-37122: Make the co_argcount attribute of code objects represent the total number of positional arguments (including positional-only arguments). The value of co_posonlyargcount can be used to distinguish which arguments are positional only, and the difference (co_argcount - co_posonlyargcount) is the number of positional-or-keyword arguments. Patch by Pablo Galindo.

  • bpo-20092: Constructors of int, float and complex will now use the __index__() special method, if available and the corresponding method __int__(), __float__() or __complex__() is not available.

  • bpo-37087: Add native thread ID (TID) support to OpenBSD.

  • bpo-26219: Implemented per opcode cache mechanism and LOAD_GLOBAL instruction use it. LOAD_GLOBAL is now about 40% faster. Contributed by Yury Selivanov, and Inada Naoki.

  • bpo-37072: Fix crash in PyAST_FromNodeObject() when flags is NULL.

  • bpo-37029: Freeing a great many small objects could take time quadratic in the number of arenas, due to using linear search to keep obmalloc.c's list of usable arenas sorted by order of number of free memory pools. This is accomplished without search now, leaving the worst-case time linear in the number of arenas. For programs where this quite visibly matters (typically with more than 100 thousand small objects alive simultaneously), this can greatly reduce the time needed to release their memory.

  • bpo-26423: Fix possible overflow in wrap_lenfunc() when sizeof(long) < sizeof(Py_ssize_t) (e.g., 64-bit Windows).

  • bpo-37050: Improve the AST for "debug" f-strings, which use '=' to print out the source of the expression being evaluated. Delete expr_text from the FormattedValue node, and instead use a Constant string node (possibly merged with adjacent constant expressions inside the f-string).

  • bpo-22385: The bytes.hex, bytearray.hex, and memoryview.hex methods as well as the binascii.hexlify and b2a_hex functions now have the ability to include an optional separator between hex bytes. This functionality was inspired by MicroPython's hexlify implementation.

  • bpo-26836: Add os.memfd_create().

  • bpo-37032: Added new replace() method to the code type (types.CodeType).

  • bpo-37007: Implement socket.if_nameindex(), socket.if_nametoindex(), and socket.if_indextoname() on Windows.

  • bpo-36829: PyErr_WriteUnraisable() now creates a traceback object if there is no current traceback. Moreover, call PyErr_NormalizeException() and PyException_SetTraceback() to normalize the exception value. Ignore any error.

  • bpo-36878: Only accept text after # type: ignore if the first character is ASCII. This is to disallow things like # type: ignoreé.

  • bpo-36878: Store text appearing after a # type: ignore comment in the AST. For example a type ignore like # type: ignore[E1000] will have the string "[E1000]" stored in its AST node.

  • bpo-2180: Treat line continuation at EOF as a SyntaxError by Anthony Sottile.

  • bpo-36907: Fix a crash when calling a C function with a keyword dict (f(**kwargs)) and changing the dict kwargs while that function is running.

  • bpo-36946: Fix possible signed integer overflow when handling slices.

  • bpo-36826: Add NamedExpression kind support to ast_unparse.c

  • bpo-1875: A SyntaxError is now raised if a code blocks that will be optimized away (e.g. if conditions that are always false) contains syntax errors. Patch by Pablo Galindo.

  • bpo-36027: Allow computation of modular inverses via three-argument pow: the second argument is now permitted to be negative in the case where the first and third arguments are relatively prime.

  • bpo-36861: Update the Unicode database to version 12.1.0.

  • bpo-28866: Avoid caching attributes of classes which type defines mro() to avoid a hard cache invalidation problem.

  • bpo-36851: The FrameType stack is now correctly cleaned up if the execution ends with a return and the stack is not empty.

  • bpo-34616: The compile() builtin functions now support the ast.PyCF_ALLOW_TOP_LEVEL_AWAIT flag, which allow to compile sources that contains top-level await, async with or async for. This is useful to evaluate async-code from with an already async functions; for example in a custom REPL.

  • bpo-36842: Implement PEP 578, adding sys.audit, io.open_code and related APIs.

  • bpo-27639: Correct return type for UserList slicing operations. Patch by Michael Blahay, Erick Cervantes, and vaultah

  • bpo-36737: Move PyRuntimeState.warnings into per-interpreter state (via "module state").

  • bpo-36793: Removed __str__ implementations from builtin types bool, int, float, complex and few classes from the standard library. They now inherit __str__() from object.

  • bpo-36817: Add a = feature f-strings for debugging. This can precede !s, !r, or !a. It produces the text of the expression, followed by an equal sign, followed by the repr of the value of the expression. So f'{3*9+15=}' would be equal to the string '3*9+15=42'. If = is specified, the default conversion is set to !r, unless a format spec is given, in which case the formatting behavior is unchanged, and __format__ will be used.

  • bpo-24048: Save the live exception during import.c's remove_module().

  • bpo-27987: pymalloc returns memory blocks aligned by 16 bytes, instead of 8 bytes, on 64-bit platforms to conform x86-64 ABI. Recent compilers assume this alignment more often. Patch by Inada Naoki.

  • bpo-36601: A long-since-meaningless check for getpid() == main_pid was removed from Python's internal C signal handler.

  • bpo-36594: Fix incorrect use of %p in format strings. Patch by Zackery Spytz.

  • bpo-36045: builtins.help() now prefixes async for async functions

  • bpo-36084: Add native thread ID (TID) to threading.Thread objects (supported platforms: Windows, FreeBSD, Linux, macOS)

  • bpo-36035: Added fix for broken symlinks in combination with pathlib

  • bpo-35983: Added new trashcan macros to deal with a double deallocation that could occur when the tp_dealloc of a subclass calls the tp_dealloc of a base class and that base class uses the trashcan mechanism. Patch by Jeroen Demeyer.

  • bpo-20602: Do not clear sys.flags and sys.float_info during shutdown. Patch by Zackery Spytz.

  • bpo-26826: Expose copy_file_range() as a low level API in the os module.

  • bpo-32388: Remove cross-version binary compatibility requirement in tp_flags.

  • bpo-31862: Port binascii to PEP 489 multiphase initialization. Patch by Marcel Plch.


  • bpo-37128: Added math.perm().

  • bpo-37120: Add SSLContext.num_tickets to control the number of TLSv1.3 session tickets.

  • bpo-12202: Fix the error handling in msilib.SummaryInformation.GetProperty(). Patch by Zackery Spytz.

  • bpo-26835: The fcntl module now contains file sealing constants for sealing of memfds.

  • bpo-29262: Add get_origin() and get_args() introspection helpers to typing module.

  • bpo-12639: msilib.Directory.start_component() no longer fails if keyfile is not None.

  • bpo-36999: Add the asyncio.Task.get_coro() method to publicly expose the tasks's coroutine object.

  • bpo-35246: Make asyncio.create_subprocess_exec() accept path-like arguments.

  • bpo-35279: Change default max_workers of ThreadPoolExecutor from cpu_count() * 5 to min(32, cpu_count() + 4). Previous value was unreasonably large on many cores machines.

  • bpo-37076: _thread.start_new_thread() now logs uncaught exception raised by the function using sys.unraisablehook(), rather than sys.excepthook(), so the hook gets access to the function which raised the exception.

  • bpo-33725: On macOS, the multiprocessing module now uses spawn start method by default.

  • bpo-37054: Fix destructor _pyio.BytesIO and _pyio.TextIOWrapper: initialize their _buffer attribute as soon as possible (in the class body), because it's used by __del__() which calls close().

  • bpo-37058: PEP 544: Add Protocol and @runtime_checkable to the typing module.

  • bpo-36933: The functions sys.set_coroutine_wrapper and sys.get_coroutine_wrapper that were deprecated and marked for removal in 3.8 have been removed.

  • bpo-37047: Handle late binding and attribute access in unittest.mock.AsyncMock setup for autospeccing. Document newly implemented async methods in unittest.mock.MagicMock.

  • bpo-37049: PEP 589: Add TypedDict to the typing module.

  • bpo-37046: PEP 586: Add Literal to the typing module.

  • bpo-37045: PEP 591: Add Final qualifier and @final decorator to the typing module.

  • bpo-37035: Don't log OSError based exceptions if a fatal error has occurred in asyncio transport. Peer can generate almost any OSError, user cannot avoid these exceptions by fixing own code. Errors are still propagated to user code, it's just logging them is pointless and pollute asyncio logs.

  • bpo-37001: symtable.symtable() now accepts the same input types for source code as the built-in compile() function. Patch by Dino Viehland.

  • bpo-37028: Implement asyncio REPL

  • bpo-37027: Return safe to use proxy socket object from transport.get_extra_info('socket')

  • bpo-32528: Make asyncio.CancelledError a BaseException.

    This will address the common mistake many asyncio users make: an "except Exception" clause breaking Tasks cancellation.

    In addition to this change, we stop inheriting asyncio.TimeoutError and asyncio.InvalidStateError from their concurrent.futures.* counterparts. There's no point for these exceptions to share the inheritance chain.

  • bpo-1230540: Add a new threading.excepthook() function which handles uncaught threading.Thread.run() exception. It can be overridden to control how uncaught threading.Thread.run() exceptions are handled.

  • bpo-36996: Handle unittest.mock.patch() used as a decorator on async functions.

  • bpo-37008: Add support for calling next() with the mock resulting from unittest.mock.mock_open()

  • bpo-27737: Allow whitespace only header encoding in email.header - by Batuhan Taskaya

  • bpo-36969: PDB command