What’s New In Python 3.12




May 31, 2023

This article explains the new features in Python 3.12, compared to 3.11.

For full details, see the changelog.


Prerelease users should be aware that this document is currently in draft form. It will be updated substantially as Python 3.12 moves towards release, so it’s worth checking back even after reading earlier versions.

Summary – Release highlights

New grammar features:

  • PEP 701: Syntactic formalization of f-strings

New typing features:

Important deprecations, removals or restrictions:

  • PEP 623: Remove wstr from Unicode

  • PEP 632: Remove the distutils package

Improved Error Messages

  • Modules from the standard library are now potentially suggested as part of the error messages displayed by the interpreter when a NameError is raised to the top level. Contributed by Pablo Galindo in gh-98254.

    >>> sys.version_info
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    NameError: name 'sys' is not defined. Did you forget to import 'sys'?
  • Improve the error suggestion for NameError exceptions for instances. Now if a NameError is raised in a method and the instance has an attribute that’s exactly equal to the name in the exception, the suggestion will include self.<NAME> instead of the closest match in the method scope. Contributed by Pablo Galindo in gh-99139.

    >>> class A:
    ...    def __init__(self):
    ...        self.blech = 1
    ...    def foo(self):
    ...        somethin = blech
    >>> A().foo()
      File "<stdin>", line 1
        somethin = blech
    NameError: name 'blech' is not defined. Did you mean: 'self.blech'?
  • Improve the SyntaxError error message when the user types import x from y instead of from y import x. Contributed by Pablo Galindo in gh-98931.

    >>> import a.y.z from b.y.z
      File "<stdin>", line 1
        import a.y.z from b.y.z
    SyntaxError: Did you mean to use 'from ... import ...' instead?
  • ImportError exceptions raised from failed from <module> import <name> statements now include suggestions for the value of <name> based on the available names in <module>. Contributed by Pablo Galindo in gh-91058.

    >>> from collections import chainmap
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ImportError: cannot import name 'chainmap' from 'collections'. Did you mean: 'ChainMap'?

New Features

PEP 701: Syntactic formalization of f-strings

PEP 701 lifts some restrictions on the usage of f-strings. Expression components inside f-strings can now be any valid Python expression including backslashes, unicode escaped sequences, multi-line expressions, comments and strings reusing the same quote as the containing f-string. Let’s cover these in detail:

  • Quote reuse: in Python 3.11, reusing the same quotes as the containing f-string raises a SyntaxError, forcing the user to either use other available quotes (like using double quotes or triple quotes if the f-string uses single quotes). In Python 3.12, you can now do things like this:

    >>> songs = ['Take me back to Eden', 'Alkaline', 'Ascensionism']
    >>> f"This is the playlist: {", ".join(songs)}"
    'This is the playlist: Take me back to Eden, Alkaline, Ascensionism'

    Note that before this change there was no explicit limit in how f-strings can be nested, but the fact that string quotes cannot be reused inside the expression component of f-strings made it impossible to nest f-strings arbitrarily. In fact, this is the most nested f-string that could be written:

    >>> f"""{f'''{f'{f"{1+1}"}'}'''}"""

    As now f-strings can contain any valid Python expression inside expression components, it is now possible to nest f-strings arbitrarily:

    >>> f"{f"{f"{f"{f"{f"{1+1}"}"}"}"}"}"
  • Multi-line expressions and comments: In Python 3.11, f-strings expressions must be defined in a single line even if outside f-strings expressions could span multiple lines (like literal lists being defined over multiple lines), making them harder to read. In Python 3.12 you can now define expressions spaning multiple lines and include comments on them:

    >>> f"This is the playlist: {", ".join([
    ...     'Take me back to Eden',  # My, my, those eyes like fire
    ...     'Alkaline',              # Not acid nor alkaline
    ...     'Ascensionism'           # Take to the broken skies at last
    ... ])}"
    'This is the playlist: Take me back to Eden, Alkaline, Ascensionism'
  • Backslashes and unicode characters: before Python 3.12 f-string expressions couldn’t contain any \ character. This also affected unicode escaped sequences (such as \N{snowman}) as these contain the \N part that previously could not be part of expression components of f-strings. Now, you can define expressions like this:

    >>> print(f"This is the playlist: {"\n".join(songs)}")
    This is the playlist: Take me back to Eden
    >>> print(f"This is the playlist: {"\N{BLACK HEART SUIT}".join(songs)}")
    This is the playlist: Take me back to Eden♥Alkaline♥Ascensionism

See PEP 701 for more details.

(Contributed by Pablo Galindo, Batuhan Taskaya, Lysandros Nikolaou, Cristián Maureira-Fredes and Marta Gómez in gh-102856. PEP written by Pablo Galindo, Batuhan Taskaya, Lysandros Nikolaou and Marta Gómez).

PEP 709: Comprehension inlining

Dictionary, list, and set comprehensions are now inlined, rather than creating a new single-use function object for each execution of the comprehension. This speeds up execution of a comprehension by up to 2x.

Comprehension iteration variables remain isolated; they don’t overwrite a variable of the same name in the outer scope, nor are they visible after the comprehension. This isolation is now maintained via stack/locals manipulation, not via separate function scope.

Inlining does result in a few visible behavior changes:

  • There is no longer a separate frame for the comprehension in tracebacks, and tracing/profiling no longer shows the comprehension as a function call.

  • Calling locals() inside a comprehension now includes variables from outside the comprehension, and no longer includes the synthetic .0 variable for the comprehension “argument”.

Contributed by Carl Meyer and Vladimir Matveev in PEP 709.

PEP 688: Making the buffer protocol accessible in Python

PEP 688 introduces a way to use the buffer protocol from Python code. Classes that implement the __buffer__() method are now usable as buffer types.

The new collections.abc.Buffer ABC provides a standard way to represent buffer objects, for example in type annotations. The new inspect.BufferFlags enum represents the flags that can be used to customize buffer creation. (Contributed by Jelle Zijlstra in gh-102500.)

Other Language Changes

  • Add Python support for the Linux perf profiler through the new environment variable PYTHONPERFSUPPORT, the new command-line option -X perf, as well as the new sys.activate_stack_trampoline(), sys.deactivate_stack_trampoline(), and sys.is_stack_trampoline_active() APIs. (Design by Pablo Galindo. Contributed by Pablo Galindo and Christian Heimes with contributions from Gregory P. Smith [Google] and Mark Shannon in gh-96123.)

  • The extraction methods in tarfile, and shutil.unpack_archive(), have a new a filter argument that allows limiting tar features than may be surprising or dangerous, such as creating files outside the destination directory. See Extraction filters for details. In Python 3.14, the default will switch to 'data'. (Contributed by Petr Viktorin in PEP 706.)

  • types.MappingProxyType instances are now hashable if the underlying mapping is hashable. (Contributed by Serhiy Storchaka in gh-87995.)

  • memoryview now supports the half-float type (the “e” format code). (Contributed by Dong-hee Na and Antoine Pitrou in gh-90751.)

  • The parser now raises SyntaxError when parsing source code containing null bytes. (Contributed by Pablo Galindo in gh-96670.)

  • ast.parse() now raises SyntaxError instead of ValueError when parsing source code containing null bytes. (Contributed by Pablo Galindo in gh-96670.)

  • The Garbage Collector now runs only on the eval breaker mechanism of the Python bytecode evaluation loop instead of object allocations. The GC can also run when PyErr_CheckSignals() is called so C extensions that need to run for a long time without executing any Python code also have a chance to execute the GC periodically. (Contributed by Pablo Galindo in gh-97922.)

  • A backslash-character pair that is not a valid escape sequence now generates a SyntaxWarning, instead of DeprecationWarning. For example, re.compile("\d+\.\d+") now emits a SyntaxWarning ("\d" is an invalid escape sequence), use raw strings for regular expression: re.compile(r"\d+\.\d+"). In a future Python version, SyntaxError will eventually be raised, instead of SyntaxWarning. (Contributed by Victor Stinner in gh-98401.)

  • Octal escapes with value larger than 0o377 (ex: "\477"), deprecated in Python 3.11, now produce a SyntaxWarning, instead of DeprecationWarning. In a future Python version they will be eventually a SyntaxError. (Contributed by Victor Stinner in gh-98401.)

  • All builtin and extension callables expecting boolean parameters now accept arguments of any type instead of just bool and int. (Contributed by Serhiy Storchaka in gh-60203.)

  • Variables used in the target part of comprehensions that are not stored to can now be used in assignment expressions (:=). For example, in [(b := 1) for a, b.prop in some_iter], the assignment to b is now allowed. Note that assigning to variables stored to in the target part of comprehensions (like a) is still disallowed, as per PEP 572. (Contributed by Nikita Sobolev in gh-100581.)

  • slice objects are now hashable, allowing them to be used as dict keys and set items. (Contributed by Will Bradshaw, Furkan Onder, and Raymond Hettinger in gh-101264.)

  • sum() now uses Neumaier summation to improve accuracy when summing floats or mixed ints and floats. (Contributed by Raymond Hettinger in gh-100425.)

  • Exceptions raised in a typeobject’s __set_name__ method are no longer wrapped by a RuntimeError. Context information is added to the exception as a PEP 678 note. (Contributed by Irit Katriel in gh-77757.)

  • When a try-except* construct handles the entire ExceptionGroup and raises one other exception, that exception is no longer wrapped in an ExceptionGroup. Also changed in version 3.11.4. (Contributed by Irit Katriel in gh-103590.)

New Modules

  • None yet.

Improved Modules








  • Pseudo instruction opcodes (which are used by the compiler but do not appear in executable bytecode) are now exposed in the dis module. HAVE_ARGUMENT is still relevant to real opcodes, but it is not useful for pseudo instructions. Use the new hasarg collection instead. (Contributed by Irit Katriel in gh-94216.)



  • Added itertools.batched() for collecting into even-sized tuples where the last batch may be shorter than the rest. (Contributed by Raymond Hettinger in gh-98363.)



  • Added math.sumprod() for computing a sum of products. (Contributed by Raymond Hettinger in gh-100485.)

  • Extended math.nextafter() to include a steps argument for moving up or down multiple steps at a time. (By Matthias Goergens, Mark Dickinson, and Raymond Hettinger in gh-94906.)


  • Add os.PIDFD_NONBLOCK to open a file descriptor for a process with os.pidfd_open() in non-blocking mode. (Contributed by Kumar Aditya in gh-93312.)

  • os.DirEntry now includes an os.DirEntry.is_junction() method to check if the entry is a junction. (Contributed by Charles Machalow in gh-99547.)

  • Add os.listdrives(), os.listvolumes() and os.listmounts() functions on Windows for enumerating drives, volumes and mount points. (Contributed by Steve Dower in gh-102519.)

  • os.stat() and os.lstat() are now more accurate on Windows. The st_birthtime field will now be filled with the creation time of the file, and st_ctime is deprecated but still contains the creation time (but in the future will return the last metadata change, for consistency with other platforms). st_dev may be up to 64 bits and st_ino up to 128 bits depending on your file system, and st_rdev is always set to zero rather than incorrect values. Both functions may be significantly faster on newer releases of Windows. (Contributed by Steve Dower in gh-99726.)



  • Add convenience variables to hold values temporarily for debug session and provide quick access to values like the current frame or the return value. (Contributed by Tian Gao in gh-103693.)



  • shutil.make_archive() now passes the root_dir argument to custom archivers which support it. In this case it no longer temporarily changes the current working directory of the process to root_dir to perform archiving. (Contributed by Serhiy Storchaka in gh-74696.)

  • shutil.rmtree() now accepts a new argument onexc which is an error handler like onerror but which expects an exception instance rather than a (typ, val, tb) triplet. onerror is deprecated and will be removed in Python 3.14. (Contributed by Irit Katriel in gh-102828.)

  • shutil.which() now consults the PATHEXT environment variable to find matches within PATH on Windows even when the given cmd includes a directory component. (Contributed by Charles Machalow in gh-103179.)

    shutil.which() will call NeedCurrentDirectoryForExePathW when querying for executables on Windows to determine if the current working directory should be prepended to the search path. (Contributed by Charles Machalow in gh-103179.)

    shutil.which() will return a path matching the cmd with a component from PATHEXT prior to a direct match elsewhere in the search path on Windows. (Contributed by Charles Machalow in gh-103179.)



  • Extended statistics.correlation() to include as a ranked method for computing the Spearman correlation of ranked data. (Contributed by Raymond Hettinger in gh-95861.)



  • tkinter.Canvas.coords() now flattens its arguments. It now accepts not only coordinates as separate arguments (x1, y1, x2, y2, ...) and a sequence of coordinates ([x1, y1, x2, y2, ...]), but also coordinates grouped in pairs ((x1, y1), (x2, y2), ... and [(x1, y1), (x2, y2), ...]), like create_*() methods. (Contributed by Serhiy Storchaka in gh-94473.)




  • The Unicode database has been updated to version 15.0.0. (Contributed by Benjamin Peterson in gh-96734).


Added --durations command line option, showing the N slowest test cases:

python3 -m unittest --durations=3 lib.tests.test_threading
Slowest test durations
1.210s     test_timeout (Lib.test.test_threading.BarrierTests)
1.003s     test_default_timeout (Lib.test.test_threading.BarrierTests)
0.518s     test_timeout (Lib.test.test_threading.EventTests)

(0.000 durations hidden.  Use -v to show these durations.)
Ran 158 tests in 9.869s

OK (skipped=3)

(Contributed by Giampaolo Rodola in bpo-4080)




  • isinstance() checks against runtime-checkable protocols now use inspect.getattr_static() rather than hasattr() to lookup whether attributes exist. This means that descriptors and __getattr__() methods are no longer unexpectedly evaluated during isinstance() checks against runtime-checkable protocols. However, it may also mean that some objects which used to be considered instances of a runtime-checkable protocol may no longer be considered instances of that protocol on Python 3.12+, and vice versa. Most users are unlikely to be affected by this change. (Contributed by Alex Waygood in gh-102433.)

  • The members of a runtime-checkable protocol are now considered “frozen” at runtime as soon as the class has been created. Monkey-patching attributes onto a runtime-checkable protocol will still work, but will have no impact on isinstance() checks comparing objects to the protocol. For example:

    >>> from typing import Protocol, runtime_checkable
    >>> @runtime_checkable
    ... class HasX(Protocol):
    ...     x = 1
    >>> class Foo: ...
    >>> f = Foo()
    >>> isinstance(f, HasX)
    >>> f.x = 1
    >>> isinstance(f, HasX)
    >>> HasX.y = 2
    >>> isinstance(f, HasX)  # unchanged, even though HasX now also has a "y" attribute

    This change was made in order to speed up isinstance() checks against runtime-checkable protocols.

  • The performance profile of isinstance() checks against runtime-checkable protocols has changed significantly. Most isinstance() checks against protocols with only a few members should be at least 2x faster than in 3.11, and some may be 20x faster or more. However, isinstance() checks against protocols with fourteen or more members may be slower than in Python 3.11. (Contributed by Alex Waygood in gh-74690 and gh-103193.)

  • All typing.TypedDict and typing.NamedTuple classes now have the __orig_bases__ attribute. (Contributed by Adrian Garcia Badaracco in gh-103699.)

  • Add frozen_default parameter to typing.dataclass_transform(). (Contributed by Erik De Bonte in gh-99957.)



  • Removed wstr and wstr_length members from Unicode objects. It reduces object size by 8 or 16 bytes on 64bit platform. (PEP 623) (Contributed by Inada Naoki in gh-92536.)

  • Added experimental support for using the BOLT binary optimizer in the build process, which improves performance by 1-5%. (Contributed by Kevin Modzelewski in gh-90536 and tuned by Dong-hee Na in gh-101525)

  • Speed up the regular expression substitution (functions re.sub() and re.subn() and corresponding re.Pattern methods) for replacement strings containing group references by 2–3 times. (Contributed by Serhiy Storchaka in gh-91524.)

  • Speed up asyncio.Task creation by deferring expensive string formatting. (Contributed by Itamar O in gh-103793.)

  • The tokenize.tokenize() and tokenize.generate_tokens() functions are up to 64% faster as a side effect of the changes required to cover PEP 701 in the tokenize module. (Contributed by Marta Gómez Macías and Pablo Galindo in gh-102856.)

CPython bytecode changes

Demos and Tools

  • Remove the Tools/demo/ directory which contained old demo scripts. A copy can be found in the old-demos project. (Contributed by Victor Stinner in gh-97681.)

  • Remove outdated example scripts of the Tools/scripts/ directory. A copy can be found in the old-demos project. (Contributed by Victor Stinner in gh-97669.)


Pending Removal in Python 3.13

The following modules and APIs have been deprecated in earlier Python releases, and will be removed in Python 3.13.

Modules (see PEP 594):


Pending Removal in Python 3.14

Pending Removal in Future Versions

The following APIs were deprecated in earlier Python versions and will be removed, although there is currently no date scheduled for their removal.

  • typing.Text (gh-92332)

  • Currently Python accepts numeric literals immediately followed by keywords, for example 0in x, 1or x, 0if 1else 2. It allows confusing and ambiguous expressions like [0x1for x in y] (which can be interpreted as [0x1 for x in y] or [0x1f or x in y]). A syntax warning is raised if the numeric literal is immediately followed by one of keywords and, else, for, if, in, is and or. In a future release it will be changed to a syntax error. (gh-87999)


  • Remove the distutils package. It was deprecated in Python 3.10 by PEP 632 “Deprecate distutils module”. For projects still using distutils and cannot be updated to something else, the setuptools project can be installed: it still provides distutils. (Contributed by Victor Stinner in gh-92584.)

  • Remove the bundled setuptools wheel from ensurepip, and stop installing setuptools in environments created by venv.

    pip (>= 22.1) does not require setuptools to be installed in the environment. setuptools-based (and distutils-based) packages can still be used with pip install, since pip will provide setuptools in the build environment it uses for building a package.

    easy_install, pkg_resources, setuptools and distutils are no longer provided by default in environments created with venv or bootstrapped with ensurepip, since they are part of the setuptools package. For projects relying on these at runtime, the setuptools project should be declared as a dependency and installed separately (typically, using pip).

    (Contributed by Pradyun Gedam in gh-95299.)

  • Removed many old deprecated unittest features:

    (Contributed by Serhiy Storchaka in bpo-45162.)

  • Several names deprecated in the configparser way back in 3.2 have been removed per gh-89336:

  • The following undocumented sqlite3 features, deprecated in Python 3.10, are now removed:

    • sqlite3.enable_shared_cache()

    • sqlite3.OptimizedUnicode

    If a shared cache must be used, open the database in URI mode using the cache=shared query parameter.

    The sqlite3.OptimizedUnicode text factory has been an alias for str since Python 3.3. Code that previously set the text factory to OptimizedUnicode can either use str explicitly, or rely on the default value which is also str.

    (Contributed by Erlend E. Aasland in gh-92548.)

  • smtpd has been removed according to the schedule in PEP 594, having been deprecated in Python 3.4.7 and 3.5.4. Use aiosmtpd PyPI module or any other asyncio-based server instead. (Contributed by Oleg Iarygin in gh-93243.)

  • asynchat and asyncore have been removed according to the schedule in PEP 594, having been deprecated in Python 3.6. Use asyncio instead. (Contributed by Nikita Sobolev in gh-96580.)

  • Remove io.OpenWrapper and _pyio.OpenWrapper, deprecated in Python 3.10: just use open() instead. The open() (io.open()) function is a built-in function. Since Python 3.10, _pyio.open() is also a static method. (Contributed by Victor Stinner in gh-94169.)

  • Remove the ssl.RAND_pseudo_bytes() function, deprecated in Python 3.6: use os.urandom() or ssl.RAND_bytes() instead. (Contributed by Victor Stinner in gh-94199.)

  • gzip: Remove the filename attribute of gzip.GzipFile, deprecated since Python 2.6, use the name attribute instead. In write mode, the filename attribute added '.gz' file extension if it was not present. (Contributed by Victor Stinner in gh-94196.)

  • Remove the ssl.match_hostname() function. It was deprecated in Python 3.7. OpenSSL performs hostname matching since Python 3.7, Python no longer uses the ssl.match_hostname() function. (Contributed by Victor Stinner in gh-94199.)

  • Remove the locale.format() function, deprecated in Python 3.7: use locale.format_string() instead. (Contributed by Victor Stinner in gh-94226.)

  • hashlib: Remove the pure Python implementation of hashlib.pbkdf2_hmac(), deprecated in Python 3.10. Python 3.10 and newer requires OpenSSL 1.1.1 (PEP 644): this OpenSSL version provides a C implementation of pbkdf2_hmac() which is faster. (Contributed by Victor Stinner in gh-94199.)

  • xml.etree.ElementTree: Remove the ElementTree.Element.copy() method of the pure Python implementation, deprecated in Python 3.10, use the copy.copy() function instead. The C implementation of xml.etree.ElementTree has no copy() method, only a __copy__() method. (Contributed by Victor Stinner in gh-94383.)

  • zipimport: Remove find_loader() and find_module() methods, deprecated in Python 3.10: use the find_spec() method instead. See PEP 451 for the rationale. (Contributed by Victor Stinner in gh-94379.)

  • Remove the ssl.wrap_socket() function, deprecated in Python 3.7: instead, create a ssl.SSLContext object and call its ssl.SSLContext.wrap_socket method. Any package that still uses ssl.wrap_socket() is broken and insecure. The function neither sends a SNI TLS extension nor validates server hostname. Code is subject to CWE-295: Improper Certificate Validation. (Contributed by Victor Stinner in gh-94199.)

  • Many previously deprecated cleanups in importlib have now been completed:

    • References to, and support for module_repr() has been removed. (Contributed by Barry Warsaw in gh-97850.)

    • importlib.util.set_package has been removed. (Contributed by Brett Cannon in gh-65961.)

    • Support for find_loader() and find_module() APIs have been removed. (Contributed by Barry Warsaw in gh-98040.)

    • importlib.abc.Finder, pkg.ImpImporter, and pkg.ImpLoader have been removed. (Contributed by Barry Warsaw in gh-98040.)

    • The imp module has been removed. (Contributed by Barry Warsaw in gh-98040.)

  • Removed the suspicious rule from the documentation Makefile, and removed Doc/tools/rstlint.py, both in favor of sphinx-lint. (Contributed by Julien Palard in gh-98179.)

  • Remove the keyfile and certfile parameters from the ftplib, imaplib, poplib and smtplib modules, and the key_file, cert_file and check_hostname parameters from the http.client module, all deprecated since Python 3.6. Use the context parameter (ssl_context in imaplib) instead. (Contributed by Victor Stinner in gh-94172.)

  • ftplib: Remove the FTP_TLS.ssl_version class attribute: use the context parameter instead. (Contributed by Victor Stinner in gh-94172.)

  • Remove support for obsolete browsers from webbrowser. Removed browsers include: Grail, Mosaic, Netscape, Galeon, Skipstone, Iceape, Firebird, and Firefox versions 35 and below (gh-102871).

Porting to Python 3.12

This section lists previously described changes and other bugfixes that may require changes to your code.

Changes in the Python API

  • More strict rules are now applied for numerical group references and group names in regular expressions. Only sequence of ASCII digits is now accepted as a numerical reference. The group name in bytes patterns and replacement strings can now only contain ASCII letters and digits and underscore. (Contributed by Serhiy Storchaka in gh-91760.)

  • Removed randrange() functionality deprecated since Python 3.10. Formerly, randrange(10.0) losslessly converted to randrange(10). Now, it raises a TypeError. Also, the exception raised for non-integral values such as randrange(10.5) or randrange('10') has been changed from ValueError to TypeError. This also prevents bugs where randrange(1e25) would silently select from a larger range than randrange(10**25). (Originally suggested by Serhiy Storchaka gh-86388.)

  • argparse.ArgumentParser changed encoding and error handler for reading arguments from file (e.g. fromfile_prefix_chars option) from default text encoding (e.g. locale.getpreferredencoding(False)) to filesystem encoding and error handler. Argument files should be encoded in UTF-8 instead of ANSI Codepage on Windows.

  • Removed the asyncore-based smtpd module deprecated in Python 3.4.7 and 3.5.4. A recommended replacement is the asyncio-based aiosmtpd PyPI module.

  • shlex.split(): Passing None for s argument now raises an exception, rather than reading sys.stdin. The feature was deprecated in Python 3.9. (Contributed by Victor Stinner in gh-94352.)

  • The os module no longer accepts bytes-like paths, like bytearray and memoryview types: only the exact bytes type is accepted for bytes strings. (Contributed by Victor Stinner in gh-98393.)

  • syslog.openlog() and syslog.closelog() now fail if used in subinterpreters. syslog.syslog() may still be used in subinterpreters, but now only if syslog.openlog() has already been called in the main interpreter. These new restrictions do not apply to the main interpreter, so only a very small set of users might be affected. This change helps with interpreter isolation. Furthermore, syslog is a wrapper around process-global resources, which are best managed from the main interpreter. (Contributed by Dong-hee Na in gh-99127.)

  • The undocumented locking behavior of cached_property() is removed, because it locked across all instances of the class, leading to high lock contention. This means that a cached property getter function could now run more than once for a single instance, if two threads race. For most simple cached properties (e.g. those that are idempotent and simply calculate a value based on other attributes of the instance) this will be fine. If synchronization is needed, implement locking within the cached property getter function or around multi-threaded access points.

  • sys._current_exceptions() now returns a mapping from thread-id to an exception instance, rather than to a (typ, exc, tb) tuple. (Contributed by Irit Katriel in gh-103176.)

  • When extracting tar files using tarfile or shutil.unpack_archive(), pass the filter argument to limit features that may be surprising or dangerous. See Extraction filters for details.

  • The output of the tokenize.tokenize() and tokenize.generate_tokens() functions is now changed due to the changes introduced in PEP 701. This means that STRING tokens are not emitted any more for f-strings and the tokens described in PEP 701 are now produced instead: FSTRING_START, FSRING_MIDDLE and FSTRING_END are now emitted for f-string “string” parts in addition to the appropriate tokens for the tokenization in the expression components. For example for the f-string f"start {1+1} end" the old version of the tokenizer emitted:

    1,0-1,18:           STRING         'f"start {1+1} end"'

    while the new version emits:

    1,0-1,2:            FSTRING_START  'f"'
    1,2-1,8:            FSTRING_MIDDLE 'start '
    1,8-1,9:            OP             '{'
    1,9-1,10:           NUMBER         '1'
    1,10-1,11:          OP             '+'
    1,11-1,12:          NUMBER         '1'
    1,12-1,13:          OP             '}'
    1,13-1,17:          FSTRING_MIDDLE ' end'
    1,17-1,18:          FSTRING_END    '"'

    Aditionally, there may be some minor behavioral changes as a consecuence of the changes required to support PEP 701. Some of these changes include:

    • Some final DEDENT tokens are now emitted within the bounds of the input. This means that for a file containing 3 lines, the old version of the tokenizer returned a DEDENT token in line 4 whilst the new version returns the token in line 3.

    • The type attribute of the tokens emitted when tokenizing some invalid Python characters such as ! has changed from ERRORTOKEN to OP.

Build Changes

  • Python no longer uses setup.py to build shared C extension modules. Build parameters like headers and libraries are detected in configure script. Extensions are built by Makefile. Most extensions use pkg-config and fall back to manual detection. (Contributed by Christian Heimes in gh-93939.)

  • va_start() with two parameters, like va_start(args, format), is now required to build Python. va_start() is no longer called with a single parameter. (Contributed by Kumar Aditya in gh-93207.)

  • CPython now uses the ThinLTO option as the default link time optimization policy if the Clang compiler accepts the flag. (Contributed by Dong-hee Na in gh-89536.)

  • Add COMPILEALL_OPTS variable in Makefile to override compileall options (default: -j0) in make install. Also merged the 3 compileall commands into a single command to build .pyc files for all optimization levels (0, 1, 2) at once. (Contributed by Victor Stinner in gh-99289.)

  • Add platform triplets for 64-bit LoongArch:

    • loongarch64-linux-gnusf

    • loongarch64-linux-gnuf32

    • loongarch64-linux-gnu

    (Contributed by Zhang Na in gh-90656.)

  • PYTHON_FOR_REGEN now require Python 3.10 or newer.

C API Changes

New Features

Porting to Python 3.12

  • Legacy Unicode APIs based on Py_UNICODE* representation has been removed. Please migrate to APIs based on UTF-8 or wchar_t*.

  • Argument parsing functions like PyArg_ParseTuple() doesn’t support Py_UNICODE* based format (e.g. u, Z) anymore. Please migrate to other formats for Unicode like s, z, es, and U.

  • tp_weaklist for all static builtin types is always NULL. This is an internal-only field on PyTypeObject but we’re pointing out the change in case someone happens to be accessing the field directly anyway. To avoid breakage, consider using the existing public C-API instead, or, if necessary, the (internal-only) _PyObject_GET_WEAKREFS_LISTPTR() macro.

  • This internal-only PyTypeObject.tp_subclasses may now not be a valid object pointer. Its type was changed to void* to reflect this. We mention this in case someone happens to be accessing the internal-only field directly.

    To get a list of subclasses, call the Python method __subclasses__() (using PyObject_CallMethod(), for example).

  • Add support of more formatting options (left aligning, octals, uppercase hexadecimals, intmax_t, ptrdiff_t, wchar_t C strings, variable width and precision) in PyUnicode_FromFormat() and PyUnicode_FromFormatV(). (Contributed by Serhiy Storchaka in gh-98836.)

  • An unrecognized format character in PyUnicode_FromFormat() and PyUnicode_FromFormatV() now sets a SystemError. In previous versions it caused all the rest of the format string to be copied as-is to the result string, and any extra arguments discarded. (Contributed by Serhiy Storchaka in gh-95781.)

  • Fixed wrong sign placement in PyUnicode_FromFormat() and PyUnicode_FromFormatV(). (Contributed by Philip Georgi in gh-95504.)

  • Extension classes wanting to add a __dict__ or weak reference slot should use Py_TPFLAGS_MANAGED_DICT and Py_TPFLAGS_MANAGED_WEAKREF instead of tp_dictoffset and tp_weaklistoffset, respectively. The use of tp_dictoffset and tp_weaklistoffset is still supported, but does not fully support multiple inheritance (gh-95589), and performance may be worse. Classes declaring Py_TPFLAGS_MANAGED_DICT should call _PyObject_VisitManagedDict() and _PyObject_ClearManagedDict() to traverse and clear their instance’s dictionaries. To clear weakrefs, call PyObject_ClearWeakRefs(), as before.

  • The PyUnicode_FSDecoder() function no longer accepts bytes-like paths, like bytearray and memoryview types: only the exact bytes type is accepted for bytes strings. (Contributed by Victor Stinner in gh-98393.)

  • The Py_CLEAR, Py_SETREF and Py_XSETREF macros now only evaluate their arguments once. If an argument has side effects, these side effects are no longer duplicated. (Contributed by Victor Stinner in gh-98724.)

  • The interpreter’s error indicator is now always normalized. This means that PyErr_SetObject(), PyErr_SetString() and the other functions that set the error indicator now normalize the exception before storing it. (Contributed by Mark Shannon in gh-101578.)

  • _Py_RefTotal is no longer authoritative and only kept around for ABI compabitility. Note that it is an internal global and only available on debug builds. If you happen to be using it then you’ll need to start using _Py_GetGlobalRefTotal().

  • The following functions now select an appropriate metaclass for the newly created type:

    Creating classes whose metaclass overrides tp_new is deprecated, and in Python 3.14+ it will be disallowed. Note that these functions ignore tp_new of the metaclass, possibly allowing incomplete initialization.

    Note that PyType_FromMetaclass() (added in Python 3.12) already disallows creating classes whose metaclass overrides tp_new.

  • PyOS_InputHook and PyOS_ReadlineFunctionPointer are no longer called in subinterpreters. This is because clients generally rely on process-wide global state (since these callbacks have no way of recovering extension module state).

    This also avoids situations where extensions may find themselves running in a subinterpreter that they don’t support (or haven’t yet been loaded in). See gh-104668 for more info.



  • Remove the token.h header file. There was never any public tokenizer C API. The token.h header file was only designed to be used by Python internals. (Contributed by Victor Stinner in gh-92651.)

  • Legacy Unicode APIs have been removed. See PEP 623 for detail.

    • PyUnicode_WCHAR_KIND

    • PyUnicode_AS_UNICODE()

    • PyUnicode_AsUnicode()

    • PyUnicode_AsUnicodeAndSize()

    • PyUnicode_AS_DATA()

    • PyUnicode_FromUnicode()

    • PyUnicode_GET_SIZE()

    • PyUnicode_GetSize()

    • PyUnicode_GET_DATA_SIZE()

  • Remove the PyUnicode_InternImmortal() function macro. (Contributed by Victor Stinner in gh-85858.)

  • Remove Jython compatibility hacks from several stdlib modules and tests. (Contributed by Nikita Sobolev in gh-99482.)

  • Remove _use_broken_old_ctypes_structure_semantics_ flag from ctypes module. (Contributed by Nikita Sobolev in gh-99285.)