What’s New In Python 3.13 (original) (raw)

Editors:

Adam Turner and Thomas Wouters

This article explains the new features in Python 3.13, compared to 3.12. Python 3.13 was released on October 7, 2024. For full details, see the changelog.

See also

PEP 719 – Python 3.13 Release Schedule

Summary – Release Highlights¶

Python 3.13 is the latest stable release of the Python programming language, with a mix of changes to the language, the implementation and the standard library. The biggest changes include a new interactive interpreter, experimental support for running in a free-threaded mode (PEP 703), and a Just-In-Time compiler (PEP 744).

Error messages continue to improve, with tracebacks now highlighted in color by default. The locals() builtin now has defined semantics for changing the returned mapping, and type parameters now support default values.

The library changes contain removal of deprecated APIs and modules, as well as the usual improvements in user-friendliness and correctness. Several legacy standard library modules have now been removed following their deprecation in Python 3.11 (PEP 594).

This article doesn’t attempt to provide a complete specification of all new features, but instead gives a convenient overview. For full details refer to the documentation, such as the Library Referenceand Language Reference. To understand the complete implementation and design rationale for a change, refer to the PEP for a particular new feature; but note that PEPs usually are not kept up-to-date once a feature has been fully implemented. See Porting to Python 3.13 for guidance on upgrading from earlier versions of Python.

Interpreter improvements:

• A greatly improved interactive interpreter andimproved error messages.
• PEP 667: The locals() builtin now hasdefined semantics when mutating the returned mapping. Python debuggers and similar tools may now more reliably update local variables in optimized scopes even during concurrent code execution.
• PEP 703: CPython 3.13 has experimental support for running with theglobal interpreter lock disabled. See Free-threaded CPython for more details.
• PEP 744: A basic JIT compiler was added. It is currently disabled by default (though we may turn it on later). Performance improvements are modest – we expect to improve this over the next few releases.
• Color support in the new interactive interpreter, as well as in tracebacksand doctest output. This can be disabled through the PYTHON_COLORS and NO_COLORenvironment variables.

Python data model improvements:

• __static_attributes__ stores the names of attributes accessed through self.X in any function in a class body.
• __firstlineno__ records the first line number of a class definition.

Significant improvements in the standard library:

• Add a new PythonFinalizationError exception, raised when an operation is blocked during finalization.
• The argparse module now supports deprecating command-line options, positional arguments, and subcommands.
• The new functions base64.z85encode() and base64.z85decode()support encoding and decoding Z85 data.
• The copy module now has a copy.replace() function, with support for many builtin types and any class defining the __replace__() method.
• The new dbm.sqlite3 module is now the default [dbm](../library/dbm.html#module-dbm "dbm: Interfaces to various Unix "database" formats.") backend.
• The os module has a suite of new functionsfor working with Linux’s timer notification file descriptors.
• The random module now has a command-line interface.

Security improvements:

• ssl.create_default_context() sets ssl.VERIFY_X509_PARTIAL_CHAINand ssl.VERIFY_X509_STRICT as default flags.

C API improvements:

• The Py_mod_gil slot is now used to indicate that an extension module supports running with the GIL disabled.
• The PyTime C API has been added, providing access to system clocks.
• PyMutex is a new lightweight mutex that occupies a single byte.
• There is a new suite of functionsfor generating PEP 669 monitoring events in the C API.

New typing features:

• PEP 696: Type parameters (typing.TypeVar, typing.ParamSpec, and typing.TypeVarTuple) now support defaults.
• PEP 702: The new warnings.deprecated() decorator adds support for marking deprecations in the type system and at runtime.
• PEP 705: typing.ReadOnly can be used to mark an item of atyping.TypedDict as read-only for type checkers.
• PEP 742: typing.TypeIs provides more intuitive type narrowing behavior, as an alternative to typing.TypeGuard.

Platform support:

• PEP 730: Apple’s iOS is now an officially supported platform, at tier 3.
• PEP 738: Android is now an officially supported platform, at tier 3.
• wasm32-wasi is now supported as a tier 2 platform.
• wasm32-emscripten is no longer an officially supported platform.

Important removals:

• PEP 594: The remaining 19 “dead batteries” (legacy stdlib modules) have been removed from the standard library:aifc, audioop, cgi, cgitb, chunk,crypt, imghdr, mailcap, msilib, nis,nntplib, ossaudiodev, pipes, sndhdr,spwd, sunau, telnetlib, uu and xdrlib.
• Remove the 2to3 tool and lib2to3 module (deprecated in Python 3.11).
• Remove the tkinter.tix module (deprecated in Python 3.6).
• Remove the locale.resetlocale() function.
• Remove the typing.io and typing.re namespaces.
• Remove chained classmethod descriptors.

Release schedule changes:

PEP 602 (“Annual Release Cycle for Python”) has been updated to extend the full support (‘bugfix’) period for new releases to two years. This updated policy means that:

• Python 3.9–3.12 have one and a half years of full support, followed by three and a half years of security fixes.
• Python 3.13 and later have two years of full support, followed by three years of security fixes.

New Features¶

A better interactive interpreter¶

Python now uses a new interactive shell by default, based on code from the PyPy project. When the user starts the REPL from an interactive terminal, the following new features are now supported:

• Multiline editing with history preservation.
• Direct support for REPL-specific commands like help, exit, and quit, without the need to call them as functions.
• Prompts and tracebacks with color enabled by default.
• Interactive help browsing using F1 with a separate command history.
• History browsing using F2 that skips output as well as the>>> and … prompts.
• “Paste mode” with F3 that makes pasting larger blocks of code easier (press F3 again to return to the regular prompt).

To disable the new interactive shell, set the PYTHON_BASIC_REPL environment variable. For more on interactive mode, see Interactive Mode.

(Contributed by Pablo Galindo Salgado, Łukasz Langa, and Lysandros Nikolaou in gh-111201 based on code from the PyPy project. Windows support contributed by Dino Viehland and Anthony Shaw.)

Improved error messages¶

• The interpreter now uses color by default when displaying tracebacks in the terminal. This feature can be controlledvia the new PYTHON_COLORS environment variable as well as the canonical NO_COLOR and FORCE_COLOR environment variables. (Contributed by Pablo Galindo Salgado in gh-112730.)
• A common mistake is to write a script with the same name as a standard library module. When this results in errors, we now display a more helpful error message:
  $ python random.py
  Traceback (most recent call last):
  File "/home/me/random.py", line 1, in
  import random
  File "/home/me/random.py", line 3, in
  print(random.randint(5))
  ^^^^^^^^^^^^^^

AttributeError: module 'random' has no attribute 'randint' (consider renaming '/home/me/random.py' since it has the same name as the standard library module named 'random' and prevents importing that standard library module)
Similarly, if a script has the same name as a third-party module that it attempts to import and this results in errors, we also display a more helpful error message:
$ python numpy.py
Traceback (most recent call last):
File "/home/me/numpy.py", line 1, in
import numpy as np
File "/home/me/numpy.py", line 3, in
np.array([1, 2, 3])
^^^^^^^^
AttributeError: module 'numpy' has no attribute 'array' (consider renaming '/home/me/numpy.py' if it has the same name as a library you intended to import)
(Contributed by Shantanu Jain in gh-95754.)

• The error message now tries to suggest the correct keyword argument when an incorrect keyword argument is passed to a function.

  "Better error messages!".split(max_split=1)
  Traceback (most recent call last):
  File "", line 1, in
  "Better error messages!".split(max_split=1)

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^
  TypeError: split() got an unexpected keyword argument 'max_split'. Did you mean 'maxsplit'?
  (Contributed by Pablo Galindo Salgado and Shantanu Jain in gh-107944.)

Free-threaded CPython¶

CPython now has experimental support for running in a free-threaded mode, with the global interpreter lock (GIL) disabled. This is an experimental feature and therefore is not enabled by default. The free-threaded mode requires a different executable, usually called python3.13t or python3.13t.exe. Pre-built binaries marked as free-threaded can be installed as part of the official Windowsand macOS installers, or CPython can be built from source with the --disable-gil option.

Free-threaded execution allows for full utilization of the available processing power by running threads in parallel on available CPU cores. While not all software will benefit from this automatically, programs designed with threading in mind will run faster on multi-core hardware.The free-threaded mode is experimental and work is ongoing to improve it: expect some bugs and a substantial single-threaded performance hit. Free-threaded builds of CPython support optionally running with the GIL enabled at runtime using the environment variable PYTHON_GIL or the command-line option -X gil=1.

To check if the current interpreter supports free-threading, python -VVand sys.version contain “experimental free-threading build”. The new sys._is_gil_enabled() function can be used to check whether the GIL is actually disabled in the running process.

C-API extension modules need to be built specifically for the free-threaded build. Extensions that support running with the GIL disabled should use the Py_mod_gil slot. Extensions using single-phase init should use PyUnstable_Module_SetGIL() to indicate whether they support running with the GIL disabled. Importing C extensions that don’t use these mechanisms will cause the GIL to be enabled, unless the GIL was explicitly disabled with the PYTHON_GIL environment variable or the-X gil=0 option. pip 24.1 or newer is required to install packages with C extensions in the free-threaded build.

This work was made possible thanks to many individuals and organizations, including the large community of contributors to Python and third-party projects to test and enable free-threading support. Notable contributors include: Sam Gross, Ken Jin, Donghee Na, Itamar Oren, Matt Page, Brett Simmers, Dino Viehland, Carl Meyer, Nathan Goldbaum, Ralf Gommers, Lysandros Nikolaou, and many others. Many of these contributors are employed by Meta, which has provided significant engineering resources to support this project.

An experimental just-in-time (JIT) compiler¶

When CPython is configured and built using the --enable-experimental-jit option, a just-in-time (JIT) compiler is added which may speed up some Python programs. On Windows, use PCbuild/build.bat --experimental-jit to enable the JIT or --experimental-jit-interpreter to enable the Tier 2 interpreter. Build requirements and further supporting information are contained at Tools/jit/README.md.

The --enable-experimental-jit option takes these (optional) values, defaulting to yes if --enable-experimental-jit is present without the optional value.

• no: Disable the entire Tier 2 and JIT pipeline.
• yes: Enable the JIT. To disable the JIT at runtime, pass the environment variable PYTHON_JIT=0.
• yes-off: Build the JIT but disable it by default. To enable the JIT at runtime, pass the environment variable PYTHON_JIT=1.
• interpreter: Enable the Tier 2 interpreter but disable the JIT. The interpreter can be disabled by running with PYTHON_JIT=0.

The internal architecture is roughly as follows:

• We start with specialized Tier 1 bytecode. See What’s new in 3.11 for details.
• When the Tier 1 bytecode gets hot enough, it gets translated to a new purely internal intermediate representation (IR), called the Tier 2 IR, and sometimes referred to as micro-ops (“uops”).
• The Tier 2 IR uses the same stack-based virtual machine as Tier 1, but the instruction format is better suited to translation to machine code.
• We have several optimization passes for Tier 2 IR, which are applied before it is interpreted or translated to machine code.
• There is a Tier 2 interpreter, but it is mostly intended for debugging the earlier stages of the optimization pipeline. The Tier 2 interpreter can be enabled by configuring Python with --enable-experimental-jit=interpreter.
• When the JIT is enabled, the optimized Tier 2 IR is translated to machine code, which is then executed.
• The machine code translation process uses a technique called_copy-and-patch_. It has no runtime dependencies, but there is a new build-time dependency on LLVM.

(JIT by Brandt Bucher, inspired by a paper by Haoran Xu and Fredrik Kjolstad. Tier 2 IR by Mark Shannon and Guido van Rossum. Tier 2 optimizer by Ken Jin.)

Defined mutation semantics for locals()¶

Historically, the expected result of mutating the return value oflocals() has been left to individual Python implementations to define. Starting from Python 3.13, PEP 667 standardises the historical behavior of CPython for most code execution scopes, but changes optimized scopes(functions, generators, coroutines, comprehensions, and generator expressions) to explicitly return independent snapshots of the currently assigned local variables, including locally referenced nonlocal variables captured in closures.

This change to the semantics of locals() in optimized scopes also affects the default behavior of code execution functions that implicitly target locals() if no explicit namespace is provided (such as exec() and eval()). In previous versions, whether or not changes could be accessed by callinglocals() after calling the code execution function was implementation-dependent. In CPython specifically, such code would typically appear to work as desired, but could sometimes fail in optimized scopes based on other code (including debuggers and code execution tracing tools) potentially resetting the shared snapshot in that scope. Now, the code will always run against an independent snapshot of the local variables in optimized scopes, and hence the changes will never be visible in subsequent calls to locals(). To access the changes made in these cases, an explicit namespace reference must now be passed to the relevant function. Alternatively, it may make sense to update affected code to use a higher level code execution API that returns the resulting code execution namespace (e.g. runpy.run_path() when executing Python files from disk).

To ensure debuggers and similar tools can reliably update local variables in scopes affected by this change, FrameType.f_locals now returns a write-through proxy to the frame’s local and locally referenced nonlocal variables in these scopes, rather than returning an inconsistently updated shared dict instance with undefined runtime semantics.

See PEP 667 for more details, including related C API changes and deprecations. Porting notes are also provided below for the affectedPython APIs and C APIs.

(PEP and implementation contributed by Mark Shannon and Tian Gao ingh-74929. Documentation updates provided by Guido van Rossum and Alyssa Coghlan.)

Support for mobile platforms¶

PEP 730: iOS is now a PEP 11 supported platform, with thearm64-apple-ios and arm64-apple-ios-simulator targets at tier 3 (iPhone and iPad devices released after 2013 and the Xcode iOS simulator running on Apple silicon hardware, respectively).x86_64-apple-ios-simulator(the Xcode iOS simulator running on older x86_64 hardware) is not a tier 3 supported platform, but will have best-effort support. (PEP written and implementation contributed by Russell Keith-Magee ingh-114099.)

PEP 738: Android is now a PEP 11 supported platform, with theaarch64-linux-android and x86_64-linux-android targets at tier 3. The 32-bit targets arm-linux-androideabi and i686-linux-androidare not tier 3 supported platforms, but will have best-effort support. (PEP written and implementation contributed by Malcolm Smith ingh-116622.)

Other Language Changes¶

• The compiler now strips common leading whitespace from every line in a docstring. This reduces the size of the bytecode cache(such as .pyc files), with reductions in file size of around 5%, for example in sqlalchemy.orm.session from SQLAlchemy 2.0. This change affects tools that use docstrings, such as doctest.

  def spam():
  ... """
  ... This is a docstring with
  ... leading whitespace.
  ...
  ... It even has multiple paragraphs!
  ... """
  ...
  spam.doc
  '\nThis is a docstring with\n leading whitespace.\n\nIt even has multiple paragraphs!\n'
  (Contributed by Inada Naoki in gh-81283.)

• Annotation scopes within class scopes can now contain lambdas and comprehensions. Comprehensions that are located within class scopes are not inlined into their parent scope.
  class C[T]:
  type Alias = lambda: T
  (Contributed by Jelle Zijlstra in gh-109118 and gh-118160.)
• Future statements are no longer triggered by relative imports of the __future__ module, meaning that statements of the form from .__future__ import ...are now simply standard relative imports, with no special features activated. (Contributed by Jeremiah Gabriel Pascual in gh-118216.)
• global declarations are now permitted in except blocks when that global is used in the else block. Previously this raised an erroneous SyntaxError. (Contributed by Irit Katriel in gh-111123.)
• Add PYTHON_FROZEN_MODULES, a new environment variable that determines whether frozen modules are ignored by the import machinery, equivalent to the -X frozen_modules command-line option. (Contributed by Yilei Yang in gh-111374.)
• Add support for the perf profiler working without frame pointers through the new environment variable PYTHON_PERF_JIT_SUPPORTand command-line option -X perf_jit. (Contributed by Pablo Galindo in gh-118518.)
• The location of a .python_history file can be changed via the new PYTHON_HISTORY environment variable. (Contributed by Levi Sabah, Zackery Spytz and Hugo van Kemenade in gh-73965.)
• Classes have a new __static_attributes__ attribute. This is populated by the compiler with a tuple of the class’s attribute names which are assigned through self.<name> from any function in its body. (Contributed by Irit Katriel in gh-115775.)
• The compiler now creates a __firstlineno__ attribute on classes with the line number of the first line of the class definition. (Contributed by Serhiy Storchaka in gh-118465.)
• The exec() and eval() builtins now accept the globals and locals arguments as keywords. (Contributed by Raphael Gaschignard in gh-105879)
• The compile() builtin now accepts a new flag,ast.PyCF_OPTIMIZED_AST, which is similar to ast.PyCF_ONLY_ASTexcept that the returned AST is optimized according to the value of the optimize argument. (Contributed by Irit Katriel in gh-108113).
• Add a __name__ attribute on property objects. (Contributed by Eugene Toder in gh-101860.)
• Add PythonFinalizationError, a new exception derived fromRuntimeError and used to signal when operations are blocked during finalization. The following callables now raise PythonFinalizationError, instead of RuntimeError:
  • _thread.start_new_thread()
  • os.fork()
  • os.forkpty()
  • subprocess.Popen
    (Contributed by Victor Stinner in gh-114570.)
• Allow the count argument of str.replace() to be a keyword. (Contributed by Hugo van Kemenade in gh-106487.)
• Many functions now emit a warning if a boolean value is passed as a file descriptor argument. This can help catch some errors earlier. (Contributed by Serhiy Storchaka in gh-82626.)
• Added name and mode attributes for compressed and archived file-like objects in the bz2, lzma, tarfile, and zipfile modules. (Contributed by Serhiy Storchaka in gh-115961.)

New Modules¶

• dbm.sqlite3: An SQLite backend for [dbm](../library/dbm.html#module-dbm "dbm: Interfaces to various Unix "database" formats."). (Contributed by Raymond Hettinger and Erlend E. Aasland in gh-100414.)

Improved Modules¶

argparse¶

• Add the deprecated parameter to theadd_argument()and add_parser() methods, to enable deprecating command-line options, positional arguments, and subcommands. (Contributed by Serhiy Storchaka in gh-83648.)

array¶

• Add the 'w' type code (Py_UCS4) for Unicode characters. It should be used instead of the deprecated 'u' type code. (Contributed by Inada Naoki in gh-80480.)
• Register array.array as a MutableSequenceby implementing the clear() method. (Contributed by Mike Zimin in gh-114894.)

ast¶

• The constructors of node types in the ast module are now stricter in the arguments they accept, with more intuitive behavior when arguments are omitted.
  If an optional field on an AST node is not included as an argument when constructing an instance, the field will now be set to None. Similarly, if a list field is omitted, that field will now be set to an empty list, and if an expr_context field is omitted, it defaults toLoad(). (Previously, in all cases, the attribute would be missing on the newly constructed AST node instance.)
  In all other cases, where a required argument is omitted, the node constructor will emit a DeprecationWarning. This will raise an exception in Python 3.15. Similarly, passing a keyword argument to the constructor that does not map to a field on the AST node is now deprecated, and will raise an exception in Python 3.15.
  These changes do not apply to user-defined subclasses of ast.ASTunless the class opts in to the new behavior by defining the AST._field_types mapping.
  (Contributed by Jelle Zijlstra in gh-105858, gh-117486, and gh-118851.)
• ast.parse() now accepts an optional argument _optimize_which is passed on to compile(). This makes it possible to obtain an optimized AST. (Contributed by Irit Katriel in gh-108113.)

asyncio¶

• asyncio.as_completed() now returns an object that is both anasynchronous iterator and a plain iteratorof awaitables. The awaitables yielded by asynchronous iteration include original task or future objects that were passed in, making it easier to associate results with the tasks being completed. (Contributed by Justin Arthur in gh-77714.)
• asyncio.loop.create_unix_server() will now automatically remove the Unix socket when the server is closed. (Contributed by Pierre Ossman in gh-111246.)
• DatagramTransport.sendto() will now send zero-length datagrams if called with an empty bytes object. The transport flow control also now accounts for the datagram header when calculating the buffer size. (Contributed by Jamie Phan in gh-115199.)
• Add Queue.shutdownand QueueShutDown to manage queue termination. (Contributed by Laurie Opperman and Yves Duprat in gh-104228.)
• Add the Server.close_clients() and Server.abort_clients()methods, which more forcefully close an asyncio server. (Contributed by Pierre Ossman in gh-113538.)
• Accept a tuple of separators in StreamReader.readuntil(), stopping when any one of them is encountered. (Contributed by Bruce Merry in gh-81322.)
• Improve the behavior of TaskGroup when an external cancellation collides with an internal cancellation. For example, when two task groups are nested and both experience an exception in a child task simultaneously, it was possible that the outer task group would hang, because its internal cancellation was swallowed by the inner task group.
  In the case where a task group is cancelled externally and also must raise an ExceptionGroup, it will now call the parent task’s cancel() method. This ensures that a CancelledError will be raised at the next await, so the cancellation is not lost.
  An added benefit of these changes is that task groups now preserve the cancellation count (cancelling()).
  In order to handle some corner cases, uncancel() may now reset the undocumented _must_cancel flag when the cancellation count reaches zero.
  (Inspired by an issue reported by Arthur Tacca in gh-116720.)
• When TaskGroup.create_task() is called on an inactiveTaskGroup, the given coroutine will be closed (which prevents a RuntimeWarning about the given coroutine being never awaited). (Contributed by Arthur Tacca and Jason Zhang in gh-115957.)
• The function and methods named create_task have received a new**kwargs argument that is passed through to the task constructor. This change was accidentally added in 3.13.3, and broke the API contract for custom task factories. Several third-party task factories implemented workarounds for this. In 3.13.4 and later releases the old factory contract is honored once again (until 3.14). To keep the workarounds working, the extra **kwargs argument still allows passing additional keyword arguments to Taskand to custom task factories.
  This affects the following function and methods:asyncio.create_task(),asyncio.loop.create_task(),asyncio.TaskGroup.create_task(). (Contributed by Thomas Grainger in gh-128307.)

base64¶

• Add z85encode() and z85decode() functions for encoding bytes as Z85 dataand decoding Z85-encoded data to bytes. (Contributed by Matan Perelman in gh-75299.)

compileall¶

• The default number of worker threads and processes is now selected usingos.process_cpu_count() instead of os.cpu_count(). (Contributed by Victor Stinner in gh-109649.)

concurrent.futures¶

• The default number of worker threads and processes is now selected usingos.process_cpu_count() instead of os.cpu_count(). (Contributed by Victor Stinner in gh-109649.)

configparser¶

• ConfigParser now has support for unnamed sections, which allows for top-level key-value pairs. This can be enabled with the new allow_unnamed_section parameter. (Contributed by Pedro Sousa Lacerda in gh-66449.)

copy¶

• The new replace() function and the replace protocol make creating modified copies of objects much simpler. This is especially useful when working with immutable objects. The following types support the replace() function and implement the replace protocol:
  • collections.namedtuple()
  • dataclasses.dataclass
  • datetime.datetime, datetime.date, datetime.time
  • inspect.Signature, inspect.Parameter
  • types.SimpleNamespace
  • code objects
    Any user-defined class can also support copy.replace() by defining the __replace__() method. (Contributed by Serhiy Storchaka in gh-108751.)

ctypes¶

• As a consequence of necessary internal refactoring, initialization of internal metaclasses now happens in __init__ rather than in __new__. This affects projects that subclass these internal metaclasses to provide custom initialization. Generally:
  • Custom logic that was done in __new__ after calling super().__new__should be moved to __init__.
  • To create a class, call the metaclass, not only the metaclass’s__new__ method.
    See gh-124520 for discussion and links to changes in some affected projects.
• ctypes.Structure objects have a new _align_attribute which allows the alignment of the structure being packed to/from memory to be specified explicitly. (Contributed by Matt Sanderson in gh-112433)

dbm¶

• Add dbm.sqlite3, a new module which implements an SQLite backend, and make it the default dbm backend. (Contributed by Raymond Hettinger and Erlend E. Aasland in gh-100414.)
• Allow removing all items from the database through the new gdbm.clear() and ndbm.clear() methods. (Contributed by Donghee Na in gh-107122.)

dis¶

• Change the output of dis module functions to show logical labels for jump targets and exception handlers, rather than offsets. The offsets can be added with the new-O command-line option or the show_offsets argument. (Contributed by Irit Katriel in gh-112137.)
• get_instructions() no longer represents cache entries as separate instructions. Instead, it returns them as part of the Instruction, in the new cache_info field. The show_caches argument to get_instructions() is deprecated and no longer has any effect. (Contributed by Irit Katriel in gh-112962.)

doctest¶

• doctest output is now colored by default. This can be controlled via the new PYTHON_COLORS environment variable as well as the canonical NO_COLORand FORCE_COLOR environment variables. See also Controlling color. (Contributed by Hugo van Kemenade in gh-117225.)
• The DocTestRunner.run() method now counts the number of skipped tests. Add the DocTestRunner.skips and TestResults.skipped attributes. (Contributed by Victor Stinner in gh-108794.)

email¶

• Headers with embedded newlines are now quoted on output. The generator will now refuse to serialize (write) headers that are improperly folded or delimited, such that they would be parsed as multiple headers or joined with adjacent data. If you need to turn this safety feature off, set verify_generated_headers. (Contributed by Bas Bloemsaat and Petr Viktorin in gh-121650.)
• getaddresses() and parseaddr() now return ('', '') pairs in more situations where invalid email addresses are encountered instead of potentially inaccurate values. The two functions have a new optional strict parameter (default True). To get the old behavior (accepting malformed input), use strict=False.getattr(email.utils, 'supports_strict_parsing', False) can be used to check if the strict parameter is available. (Contributed by Thomas Dwyer and Victor Stinner for gh-102988 to improve the CVE 2023-27043 fix.)

enum¶

• EnumDict has been made public to better support subclassingEnumType.

fractions¶

• Fraction objects now support the standardformat specification mini-language rules for fill, alignment, sign handling, minimum width, and grouping. (Contributed by Mark Dickinson in gh-111320.)

glob¶

• Add translate(), a function to convert a path specification with shell-style wildcards to a regular expression. (Contributed by Barney Gale in gh-72904.)

importlib¶

• The following functions in importlib.resources now allow accessing a directory (or tree) of resources, using multiple positional arguments (the encoding and errors arguments in the text-reading functions are now keyword-only):
  • is_resource()
  • open_binary()
  • open_text()
  • path()
  • read_binary()
  • read_text()
    These functions are no longer deprecated and are not scheduled for removal. (Contributed by Petr Viktorin in gh-116608.)
• contents() remains deprecated in favor of the fully-featured Traversable API. However, there is now no plan to remove it. (Contributed by Petr Viktorin in gh-116608.)

io¶

• The IOBase finalizer now logs any errors raised by the close() method with sys.unraisablehook. Previously, errors were ignored silently by default, and only logged in Python Development Modeor when using a Python debug build. (Contributed by Victor Stinner in gh-62948.)

ipaddress¶

• Add the IPv4Address.ipv6_mapped property, which returns the IPv4-mapped IPv6 address. (Contributed by Charles Machalow in gh-109466.)
• Fix is_global and is_private behavior inIPv4Address, IPv6Address,IPv4Network, and IPv6Network. (Contributed by Jakub Stasiak in gh-113171.)

itertools¶

• batched() has a new strict parameter, which raises a ValueError if the final batch is shorter than the specified batch size. (Contributed by Raymond Hettinger in gh-113202.)

marshal¶

• Add the allow_code parameter in module functions. Passing allow_code=False prevents serialization and de-serialization of code objects which are incompatible between Python versions. (Contributed by Serhiy Storchaka in gh-113626.)

math¶

• The new function fma() performs fused multiply-add operations. This computes x * y + z with only a single round, and so avoids any intermediate loss of precision. It wraps the fma() function provided by C99, and follows the specification of the IEEE 754 “fusedMultiplyAdd” operation for special cases. (Contributed by Mark Dickinson and Victor Stinner in gh-73468.)

mimetypes¶

• Add the guess_file_type() function to guess a MIME type from a filesystem path. Using paths with guess_type() is now soft deprecated. (Contributed by Serhiy Storchaka in gh-66543.)

mmap¶

• mmap is now protected from crashing on Windows when the mapped memory is inaccessible due to file system errors or access violations. (Contributed by Jannis Weigend in gh-118209.)
• mmap has a new seekable() method that can be used when a seekable file-like object is required. The seek() method now returns the new absolute position. (Contributed by Donghee Na and Sylvie Liberman in gh-111835.)
• The new UNIX-only trackfd parameter for mmap controls file descriptor duplication; if false, the file descriptor specified by fileno will not be duplicated. (Contributed by Zackery Spytz and Petr Viktorin in gh-78502.)

multiprocessing¶

• The default number of worker threads and processes is now selected usingos.process_cpu_count() instead of os.cpu_count(). (Contributed by Victor Stinner in gh-109649.)

os¶

• Add process_cpu_count() function to get the number of logical CPU cores usable by the calling thread of the current process. (Contributed by Victor Stinner in gh-109649.)
• cpu_count() and process_cpu_count() can be overridden through the new environment variable PYTHON_CPU_COUNTor the new command-line option -X cpu_count. This option is useful for users who need to limit CPU resources of a container system without having to modify application code or the container itself. (Contributed by Donghee Na in gh-109595.)
• Add a low level interface to Linux’s_timer file descriptors_via timerfd_create(),timerfd_settime(), timerfd_settime_ns(),timerfd_gettime(), timerfd_gettime_ns(),TFD_NONBLOCK, TFD_CLOEXEC,TFD_TIMER_ABSTIME, and TFD_TIMER_CANCEL_ON_SET(Contributed by Masaru Tsuchiyama in gh-108277.)
• lchmod() and the follow_symlinks argument of chmod()are both now available on Windows. Note that the default value of _follow_symlinks_in lchmod() is False on Windows. (Contributed by Serhiy Storchaka in gh-59616.)
• fchmod() and support for file descriptors in chmod()are both now available on Windows. (Contributed by Serhiy Storchaka in gh-113191.)
• On Windows, mkdir() and makedirs() now support passing a mode value of 0o700 to apply access control to the new directory. This implicitly affects tempfile.mkdtemp()and is a mitigation for CVE 2024-4030. Other values for mode continue to be ignored. (Contributed by Steve Dower in gh-118486.)
• posix_spawn() now accepts None for the env argument, which makes the newly spawned process use the current process environment. (Contributed by Jakub Kulik in gh-113119.)
• posix_spawn() can now use the POSIX_SPAWN_CLOSEFROMattribute in the file_actions parameter on platforms that supportposix_spawn_file_actions_addclosefrom_np(). (Contributed by Jakub Kulik in gh-113117.)

os.path¶

• Add isreserved() to check if a path is reserved on the current system. This function is only available on Windows. (Contributed by Barney Gale in gh-88569.)
• On Windows, isabs() no longer considers paths starting with exactly one slash (\ or /) to be absolute. (Contributed by Barney Gale and Jon Foster in gh-44626.)
• realpath() now resolves MS-DOS style file names even if the file is not accessible. (Contributed by Moonsik Park in gh-82367.)

pathlib¶

• Add UnsupportedOperation, which is raised instead ofNotImplementedError when a path operation isn’t supported. (Contributed by Barney Gale in gh-89812.)
• Add a new constructor for creating Path objects from ‘file’ URIs (file:///), Path.from_uri(). (Contributed by Barney Gale in gh-107465.)
• Add PurePath.full_match() for matching paths with shell-style wildcards, including the recursive wildcard “**”. (Contributed by Barney Gale in gh-73435.)
• Add the PurePath.parser class attribute to store the implementation of os.path used for low-level path parsing and joining. This will be either posixpath or ntpath.
• Add recurse_symlinks keyword-only argument toPath.glob() and rglob(). (Contributed by Barney Gale in gh-77609.)
• Path.glob() and rglob()now return files and directories when given a pattern that ends with “**”. Previously, only directories were returned. (Contributed by Barney Gale in gh-70303.)
• Add the follow_symlinks keyword-only argument toPath.is_file,Path.is_dir,Path.owner(), and Path.group(). (Contributed by Barney Gale in gh-105793 and Kamil Turek in gh-107962.)

pdb¶

• breakpoint() and set_trace() now enter the debugger immediately rather than on the next line of code to be executed. This change prevents the debugger from breaking outside of the context when breakpoint() is positioned at the end of the context. (Contributed by Tian Gao in gh-118579.)
• sys.path[0] is no longer replaced by the directory of the script being debugged when sys.flags.safe_path is set. (Contributed by Tian Gao and Christian Walther in gh-111762.)
• zipapp is now supported as a debugging target. (Contributed by Tian Gao in gh-118501.)
• Add ability to move between chained exceptions during post-mortem debugging in pm() using the new exceptions [exc_number] command for Pdb. (Contributed by Matthias Bussonnier in gh-106676.)
• Expressions and statements whose prefix is a pdb command are now correctly identified and executed. (Contributed by Tian Gao in gh-108464.)

queue¶

• Add Queue.shutdown and ShutDownto manage queue termination. (Contributed by Laurie Opperman and Yves Duprat in gh-104750.)

random¶

• Add a command-line interface. (Contributed by Hugo van Kemenade in gh-118131.)

re¶

• Rename re.error to PatternError for improved clarity.re.error is kept for backward compatibility.

shutil¶

• Support the dir_fd and follow_symlinks keyword arguments in chown(). (Contributed by Berker Peksag and Tahia K in gh-62308)

site¶

• .pth files are now decoded using UTF-8 first, and then with the locale encoding if UTF-8 decoding fails. (Contributed by Inada Naoki in gh-117802.)

sqlite3¶

• A ResourceWarning is now emitted if a Connectionobject is not closed explicitly. (Contributed by Erlend E. Aasland in gh-105539.)
• Add the filter keyword-only parameter to Connection.iterdump()for filtering database objects to dump. (Contributed by Mariusz Felisiak in gh-91602.)

ssl¶

• The create_default_context() API now includesVERIFY_X509_PARTIAL_CHAIN and VERIFY_X509_STRICTin its default flags.
  Note
  VERIFY_X509_STRICT may reject pre-RFC 5280or malformed certificates that the underlying OpenSSL implementation might otherwise accept. Whilst disabling this is not recommended, you can do so using:
  import ssl
  ctx = ssl.create_default_context()
  ctx.verify_flags &= ~ssl.VERIFY_X509_STRICT
  (Contributed by William Woodruff in gh-112389.)

statistics¶

• Add kde() for kernel density estimation. This makes it possible to estimate a continuous probability density function from a fixed number of discrete samples. (Contributed by Raymond Hettinger in gh-115863.)
• Add kde_random() for sampling from an estimated probability density function created by kde(). (Contributed by Raymond Hettinger in gh-115863.)

subprocess¶

• The subprocess module now uses the posix_spawn() function in more situations.
  Notably, when close_fds is True (the default),posix_spawn() will be used when the C library providesposix_spawn_file_actions_addclosefrom_np(), which includes recent versions of Linux, FreeBSD, and Solaris. On Linux, this should perform similarly to the existing Linux vfork() based code.
  A private control knob subprocess._USE_POSIX_SPAWN can be set to False if you need to force subprocessto never use posix_spawn(). Please report your reason and platform details in the issue tracker if you set this so that we can improve our API selection logic for everyone. (Contributed by Jakub Kulik in gh-113117.)

sys¶

• Add the _is_interned() function to test if a string was interned. This function is not guaranteed to exist in all implementations of Python. (Contributed by Serhiy Storchaka in gh-78573.)

tempfile¶

• On Windows, the default mode 0o700 used by tempfile.mkdtemp() now limits access to the new directory due to changes to os.mkdir(). This is a mitigation for CVE 2024-4030. (Contributed by Steve Dower in gh-118486.)

time¶

• On Windows, monotonic() now uses theQueryPerformanceCounter() clock for a resolution of 1 microsecond, instead of the GetTickCount64() clock which has a resolution of 15.6 milliseconds. (Contributed by Victor Stinner in gh-88494.)
• On Windows, time() now uses theGetSystemTimePreciseAsFileTime() clock for a resolution of 1 microsecond, instead of the GetSystemTimeAsFileTime() clock which has a resolution of 15.6 milliseconds. (Contributed by Victor Stinner in gh-63207.)

tkinter¶

• Add tkinter widget methods:tk_busy_hold(), tk_busy_configure(),tk_busy_cget(), tk_busy_forget(),tk_busy_current(), and tk_busy_status(). (Contributed by Miguel, klappnase and Serhiy Storchaka in gh-72684.)
• The tkinter widget method wm_attributes() now accepts the attribute name without the minus prefix to get window attributes, for example w.wm_attributes('alpha')and allows specifying attributes and values to set as keyword arguments, for example w.wm_attributes(alpha=0.5). (Contributed by Serhiy Storchaka in gh-43457.)
• wm_attributes() can now return attributes as a dict, by using the new optional keyword-only parameter return_python_dict. (Contributed by Serhiy Storchaka in gh-43457.)
• Text.count() can now return a simple intwhen the new optional keyword-only parameter return_ints is used. Otherwise, the single count is returned as a 1-tuple or None. (Contributed by Serhiy Storchaka in gh-97928.)
• Support the “vsapi” element type in the element_create() method oftkinter.ttk.Style. (Contributed by Serhiy Storchaka in gh-68166.)
• Add the after_info() method for Tkinter widgets. (Contributed by Cheryl Sabella in gh-77020.)
• Add a new copy_replace() method to PhotoImageto copy a region from one image to another, possibly with pixel zooming, subsampling, or both. (Contributed by Serhiy Storchaka in gh-118225.)
• Add from_coords parameter to the PhotoImage methodscopy(), zoom() and subsample(). Add zoom and subsample parameters to the PhotoImage methodcopy(). (Contributed by Serhiy Storchaka in gh-118225.)
• Add the PhotoImage methodsread() to read an image from a file and data() to get the image data. Add background and grayscale parameters to the write() method. (Contributed by Serhiy Storchaka in gh-118271.)

traceback¶

• Add the exc_type_str attribute to TracebackException, which holds a string display of the exc_type. Deprecate the exc_type attribute, which holds the type object itself. Add parameter save_exc_type (default True) to indicate whether exc_type should be saved. (Contributed by Irit Katriel in gh-112332.)
• Add a new show_group keyword-only parameter toTracebackException.format_exception_only() to (recursively) format the nested exceptions of a BaseExceptionGroup instance. (Contributed by Irit Katriel in gh-105292.)

types¶

• SimpleNamespace can now take a single positional argument to initialise the namespace’s arguments. This argument must either be a mapping or an iterable of key-value pairs. (Contributed by Serhiy Storchaka in gh-108191.)

typing¶

• PEP 705: Add ReadOnly, a special typing construct to mark a TypedDict item as read-only for type checkers.
• PEP 742: Add TypeIs, a typing construct that can be used to instruct a type checker how to narrow a type.
• Add NoDefault, a sentinel object used to represent the defaults of some parameters in the typing module. (Contributed by Jelle Zijlstra in gh-116126.)
• Add get_protocol_members() to return the set of members defining a typing.Protocol. (Contributed by Jelle Zijlstra in gh-104873.)
• Add is_protocol() to check whether a class is a Protocol. (Contributed by Jelle Zijlstra in gh-104873.)
• ClassVar can now be nested in Final, and vice versa. (Contributed by Mehdi Drissi in gh-89547.)

unicodedata¶

• Update the Unicode database to version 15.1.0. (Contributed by James Gerity in gh-109559.)

venv¶

• Add support for creating source control management (SCM) ignore files in a virtual environment’s directory. By default, Git is supported. This is implemented as opt-in via the API, which can be extended to support other SCMs (EnvBuilder and create()), and opt-out via the CLI, using --without-scm-ignore-files. (Contributed by Brett Cannon in gh-108125.)

warnings¶

• PEP 702: The new warnings.deprecated() decorator provides a way to communicate deprecations to a static type checkerand to warn on usage of deprecated classes and functions. A DeprecationWarning may also be emitted when a decorated function or class is used at runtime. (Contributed by Jelle Zijlstra in gh-104003.)

xml¶

• Allow controlling Expat >=2.6.0 reparse deferral (CVE 2023-52425) by adding five new methods:
  • xml.etree.ElementTree.XMLParser.flush()
  • xml.etree.ElementTree.XMLPullParser.flush()
  • xml.parsers.expat.xmlparser.GetReparseDeferralEnabled()
  • xml.parsers.expat.xmlparser.SetReparseDeferralEnabled()
  • xml.sax.expatreader.ExpatParser.flush()
    (Contributed by Sebastian Pipping in gh-115623.)
• Add the close() method for the iterator returned byiterparse() for explicit cleanup. (Contributed by Serhiy Storchaka in gh-69893.)

zipimport¶

• Add support for ZIP64 format files. Everybody loves huge data, right? (Contributed by Tim Hatch in gh-94146.)

Optimizations¶

• Several standard library modules have had their import times significantly improved. For example, the import time of the typing module has been reduced by around a third by removing dependencies on re and contextlib. Other modules to enjoy import-time speedups includeemail.utils, enum, functools,importlib.metadata, and threading. (Contributed by Alex Waygood, Shantanu Jain, Adam Turner, Daniel Hollas, and others in gh-109653.)
• textwrap.indent() is now around 30% faster than before for large input. (Contributed by Inada Naoki in gh-107369.)
• The subprocess module now uses the posix_spawn() function in more situations, including when close_fds is True (the default) on many modern platforms. This should provide a notable performance increase when launching processes on FreeBSD and Solaris. See the subprocess section above for details. (Contributed by Jakub Kulik in gh-113117.)

Removed Modules And APIs¶

PEP 594: Remove “dead batteries” from the standard library¶

PEP 594 proposed removing 19 modules from the standard library, colloquially referred to as ‘dead batteries’ due to their historic, obsolete, or insecure status. All of the following modules were deprecated in Python 3.11, and are now removed:

• aifc
  • standard-aifc: Use the redistribution of aifc library from PyPI.
• audioop
  • audioop-lts: Use audioop-lts library from PyPI.
• chunk
  • standard-chunk: Use the redistribution of chunk library from PyPI.
• cgi and cgitb
  • cgi.FieldStorage can typically be replaced withurllib.parse.parse_qsl() for GET and HEAD requests, and the email.message module or the multipart library for POST and PUT requests.
  • cgi.parse() can be replaced by callingurllib.parse.parse_qs() directly on the desired query string, unless the input is multipart/form-data, which should be replaced as described below for cgi.parse_multipart().
  • cgi.parse_header() can be replaced with the functionality in the email package, which implements the same MIME RFCs. For example, with email.message.EmailMessage:
    from email.message import EmailMessage
    msg = EmailMessage()
    msg['content-type'] = 'application/json; charset="utf8"'
    main, params = msg.get_content_type(), msg['content-type'].params
  • cgi.parse_multipart() can be replaced with the functionality in the email package, which implements the same MIME RFCs, or with the multipart library. For example, the email.message.EmailMessageand email.message.Message classes.
  • standard-cgi: and standard-cgitb: Use the redistribution of cgi and cgitb library from PyPI.
• crypt and the private _crypt extension. The hashlib module may be an appropriate replacement when simply hashing a value is required. Otherwise, various third-party libraries on PyPI are available:
  • bcrypt: Modern password hashing for your software and your servers.
  • passlib: Comprehensive password hashing framework supporting over 30 schemes.
  • argon2-cffi: The secure Argon2 password hashing algorithm.
  • legacycrypt:ctypes wrapper to the POSIX crypt library call and associated functionality.
  • crypt_r: Fork of the crypt module, wrapper to the crypt_r(3) library call and associated functionality.
  • standard-crypt and deprecated-crypt-alternative: Use the redistribution of crypt and reimplementation of _crypt libraries from PyPI.
• imghdr: The filetype, puremagic, or python-magic libraries should be used as replacements. For example, the puremagic.what() function can be used to replace the imghdr.what() function for all file formats that were supported by imghdr.
  • standard-imghdr: Use the redistribution of imghdr library from PyPI.
• mailcap: Use the mimetypes module instead.
  • standard-mailcap: Use the redistribution of mailcap library from PyPI.
• msilib
• nis
• nntplib: Use the pynntp library from PyPI instead.
  • standard-nntplib: Use the redistribution of nntplib library from PyPI.
• ossaudiodev: For audio playback, use the pygame library from PyPI instead.
• pipes: Use the subprocess module instead. Use shlex.quote() to replace the undocumented pipes.quotefunction.
  • standard-pipes: Use the redistribution of pipes library from PyPI.
• sndhdr: The filetype, puremagic, or python-magic libraries should be used as replacements.
  • standard-sndhdr: Use the redistribution of sndhdr library from PyPI.
• spwd: Use the python-pam library from PyPI instead.
• sunau
  • standard-sunau: Use the redistribution of sunau library from PyPI.
• telnetlib, Use the telnetlib3 or Exscript libraries from PyPI instead.
  • standard-telnetlib: Use the redistribution of telnetlib library from PyPI.
• uu: Use the base64 module instead, as a modern alternative.
  • standard-uu: Use the redistribution of uu library from PyPI.
• xdrlib
  • standard-xdrlib: Use the redistribution of xdrlib library from PyPI.

(Contributed by Victor Stinner and Zachary Ware in gh-104773 and gh-104780.)

2to3¶

• Remove the 2to3 program and the lib2to3 module, previously deprecated in Python 3.11. (Contributed by Victor Stinner in gh-104780.)

builtins¶

• Remove support for chained classmethod descriptors (introduced in gh-63272). These can no longer be used to wrap other descriptors, such as property. The core design of this feature was flawed and led to several problems. To “pass-through” a classmethod, consider using the __wrapped__ attribute that was added in Python 3.10. (Contributed by Raymond Hettinger in gh-89519.)
• Raise a RuntimeError when calling frame.clear()on a suspended frame (as has always been the case for an executing frame). (Contributed by Irit Katriel in gh-79932.)

configparser¶

• Remove the undocumented LegacyInterpolation class, deprecated in the docstring since Python 3.2, and at runtime since Python 3.11. (Contributed by Hugo van Kemenade in gh-104886.)

importlib.metadata¶

• Remove deprecated subscript (__getitem__()) access forEntryPoint objects. (Contributed by Jason R. Coombs in gh-113175.)

locale¶

• Remove the locale.resetlocale() function, deprecated in Python 3.11. Use locale.setlocale(locale.LC_ALL, "") instead. (Contributed by Victor Stinner in gh-104783.)

opcode¶

• Move opcode.ENABLE_SPECIALIZATION to _opcode.ENABLE_SPECIALIZATION. This field was added in 3.12, it was never documented, and is not intended for external use. (Contributed by Irit Katriel in gh-105481.)
• Remove opcode.is_pseudo(), opcode.MIN_PSEUDO_OPCODE, and opcode.MAX_PSEUDO_OPCODE, which were added in Python 3.12, but were neither documented nor exposed through dis, and were not intended to be used externally. (Contributed by Irit Katriel in gh-105481.)

optparse¶

• This module is no longer considered soft deprecated. While argparse remains preferred for new projects that aren’t using a third party command line argument processing library, there are aspects of the way argparse works that mean the lower level optparse module may provide a better foundation for writing argument processing libraries, and for implementing command line applications which adhere more strictly than argparse does to various Unix command line processing conventions that originate in the behaviour of the C getopt() function . (Contributed by Alyssa Coghlan and Serhiy Storchaka in gh-126180.)

pathlib¶

• Remove the ability to use Path objects as context managers. This functionality was deprecated and has had no effect since Python 3.9. (Contributed by Barney Gale in gh-83863.)

re¶

• Remove the undocumented, deprecated, and brokenre.template() function and re.TEMPLATE / re.T flag. (Contributed by Serhiy Storchaka and Nikita Sobolev in gh-105687.)

tkinter.tix¶

• Remove the tkinter.tix module, deprecated in Python 3.6. The third-party Tix library which the module wrapped is unmaintained. (Contributed by Zachary Ware in gh-75552.)

turtle¶

• Remove the RawTurtle.settiltangle() method, deprecated in the documentation since Python 3.1 and at runtime since Python 3.11. (Contributed by Hugo van Kemenade in gh-104876.)

typing¶

• Remove the typing.io and typing.re namespaces, deprecated since Python 3.8. The items in those namespaces can be imported directly from the typing module. (Contributed by Sebastian Rittau in gh-92871.)
• Remove the keyword-argument method of creatingTypedDict types, deprecated in Python 3.11. (Contributed by Tomas Roun in gh-104786.)

unittest¶

• Remove the following unittest functions, deprecated in Python 3.11:
  • unittest.findTestCases()
  • unittest.makeSuite()
  • unittest.getTestCaseNames()
    Use TestLoader methods instead:
  • loadTestsFromModule()
  • loadTestsFromTestCase()
  • getTestCaseNames()
    (Contributed by Hugo van Kemenade in gh-104835.)
• Remove the untested and undocumented TestProgram.usageExit()method, deprecated in Python 3.11. (Contributed by Hugo van Kemenade in gh-104992.)

urllib¶

• Remove the cafile, capath, and cadefault parameters of theurllib.request.urlopen() function, deprecated in Python 3.6. Use the context parameter instead with an SSLContext instance. The ssl.SSLContext.load_cert_chain() function can be used to load specific certificates, or let ssl.create_default_context() select the operating system’s trusted certificate authority (CA) certificates. (Contributed by Victor Stinner in gh-105382.)

webbrowser¶

• Remove the untested and undocumented MacOSX class, deprecated in Python 3.11. Use the MacOSXOSAScript class (introduced in Python 3.2) instead. (Contributed by Hugo van Kemenade in gh-104804.)
• Remove the deprecated MacOSXOSAScript._name attribute. Use the MacOSXOSAScript.nameattribute instead. (Contributed by Nikita Sobolev in gh-105546.)

New Deprecations¶

• User-defined functions:
  • Deprecate assignment to a function’s __code__ attribute, where the new code object’s type does not match the function’s type. The different types are: plain function, generator, async generator, and coroutine. (Contributed by Irit Katriel in gh-81137.)
• array:
  • Deprecate the 'u' format code (wchar_t) at runtime. This format code has been deprecated in documentation since Python 3.3, and will be removed in Python 3.16. Use the 'w' format code (Py_UCS4) for Unicode characters instead. (Contributed by Hugo van Kemenade in gh-80480.)
• ctypes:
  • Deprecate the undocumented SetPointerType() function, to be removed in Python 3.15. (Contributed by Victor Stinner in gh-105733.)
  • Soft-deprecate the ARRAY()function in favour of type * length multiplication. (Contributed by Victor Stinner in gh-105733.)
• decimal:
  • Deprecate the non-standard and undocumented Decimalformat specifier 'N', which is only supported in the decimal module’s C implementation. (Contributed by Serhiy Storchaka in gh-89902.)
• dis:
  • Deprecate the HAVE_ARGUMENT separator. Check membership in hasarg instead. (Contributed by Irit Katriel in gh-109319.)
• gettext:
  • Deprecate non-integer numbers as arguments to functions and methods that consider plural forms in the gettext module, even if no translation was found. (Contributed by Serhiy Storchaka in gh-88434.)
• glob:
  • Deprecate the undocumented glob0() and glob1() functions. Use glob() and pass a path-like object specifying the root directory to the root_dir parameter instead. (Contributed by Barney Gale in gh-117337.)
• http.server:
  • Deprecate CGIHTTPRequestHandler, to be removed in Python 3.15. Process-based CGI HTTP servers have been out of favor for a very long time. This code was outdated, unmaintained, and rarely used. It has a high potential for both security and functionality bugs. (Contributed by Gregory P. Smith in gh-109096.)
  • Deprecate the --cgi flag to the python -m http.server command-line interface, to be removed in Python 3.15. (Contributed by Gregory P. Smith in gh-109096.)
• mimetypes:
  • Soft-deprecate file path arguments to guess_type(), use guess_file_type() instead. (Contributed by Serhiy Storchaka in gh-66543.)
• re:
  • Deprecate passing the optional maxsplit, count, or flags arguments as positional arguments to the module-levelsplit(), sub(), and subn() functions. These parameters will become keyword-onlyin a future version of Python. (Contributed by Serhiy Storchaka in gh-56166.)
• pathlib:
  • Deprecate PurePath.is_reserved(), to be removed in Python 3.15. Use os.path.isreserved() to detect reserved paths on Windows. (Contributed by Barney Gale in gh-88569.)
• platform:
  • Deprecate platform.java_ver(), to be removed in Python 3.15. This function is only useful for Jython support, has a confusing API, and is largely untested. (Contributed by Nikita Sobolev in gh-116349.)
• pydoc:
  • Deprecate the undocumented ispackage() function. (Contributed by Zackery Spytz in gh-64020.)
• sqlite3:
  • Deprecate passing more than one positional argument to the connect() function and the Connection constructor. The remaining parameters will become keyword-only in Python 3.15. (Contributed by Erlend E. Aasland in gh-107948.)
  • Deprecate passing name, number of arguments, and the callable as keyword arguments for Connection.create_function()and Connection.create_aggregate()These parameters will become positional-only in Python 3.15. (Contributed by Erlend E. Aasland in gh-108278.)
  • Deprecate passing the callback callable by keyword for theset_authorizer(),set_progress_handler(), andset_trace_callback() Connection methods. The callback callables will become positional-only in Python 3.15. (Contributed by Erlend E. Aasland in gh-108278.)
• sys:
  • Deprecate the _enablelegacywindowsfsencoding() function, to be removed in Python 3.16. Use the PYTHONLEGACYWINDOWSFSENCODING environment variable instead. (Contributed by Inada Naoki in gh-73427.)
• tarfile:
  • Deprecate the undocumented and unused TarFile.tarfile attribute, to be removed in Python 3.16. (Contributed in gh-115256.)
• traceback:
  • Deprecate the TracebackException.exc_type attribute. Use TracebackException.exc_type_str instead. (Contributed by Irit Katriel in gh-112332.)
• typing:
  • Deprecate the undocumented keyword argument syntax for creatingNamedTuple classes (e.g. Point = NamedTuple("Point", x=int, y=int)), to be removed in Python 3.15. Use the class-based syntax or the functional syntax instead. (Contributed by Alex Waygood in gh-105566.)
  • Deprecate omitting the fields parameter when creating a NamedTuple or typing.TypedDict class, and deprecate passing None to the fields parameter of both types. Python 3.15 will require a valid sequence for the fields parameter. To create a NamedTuple class with zero fields, use class NT(NamedTuple): pass or NT = NamedTuple("NT", ()). To create a TypedDict class with zero fields, use class TD(TypedDict): pass or TD = TypedDict("TD", {}). (Contributed by Alex Waygood in gh-105566 and gh-105570.)
  • Deprecate the typing.no_type_check_decorator() decorator function, to be removed in in Python 3.15. After eight years in the typing module, it has yet to be supported by any major type checker. (Contributed by Alex Waygood in gh-106309.)
  • Deprecate typing.AnyStr. In Python 3.16, it will be removed from typing.__all__, and a DeprecationWarning will be emitted at runtime when it is imported or accessed. It will be removed entirely in Python 3.18. Use the new type parameter syntax instead. (Contributed by Michael The in gh-107116.)
• wave:
  • Deprecate the getmark(), setmark() and getmarkers() methods of the Wave_read and Wave_write classes, to be removed in Python 3.15. (Contributed by Victor Stinner in gh-105096.)

Pending removal in Python 3.14¶

• argparse: The type, choices, and metavar parameters of argparse.BooleanOptionalAction are deprecated and will be removed in 3.14. (Contributed by Nikita Sobolev in gh-92248.)
• ast: The following features have been deprecated in documentation since Python 3.8, now cause a DeprecationWarning to be emitted at runtime when they are accessed or used, and will be removed in Python 3.14:
  • ast.Num
  • ast.Str
  • ast.Bytes
  • ast.NameConstant
  • ast.Ellipsis
    Use ast.Constant instead. (Contributed by Serhiy Storchaka in gh-90953.)
• asyncio:
  • The child watcher classes asyncio.MultiLoopChildWatcher,asyncio.FastChildWatcher, asyncio.AbstractChildWatcherand asyncio.SafeChildWatcher are deprecated and will be removed in Python 3.14. (Contributed by Kumar Aditya in gh-94597.)
  • asyncio.set_child_watcher(), asyncio.get_child_watcher(),asyncio.AbstractEventLoopPolicy.set_child_watcher() andasyncio.AbstractEventLoopPolicy.get_child_watcher() are deprecated and will be removed in Python 3.14. (Contributed by Kumar Aditya in gh-94597.)
  • The get_event_loop() method of the default event loop policy now emits a DeprecationWarning if there is no current event loop set and it decides to create one. (Contributed by Serhiy Storchaka and Guido van Rossum in gh-100160.)
• collections.abc: Deprecated collections.abc.ByteString. Prefer Sequence or Buffer. For use in typing, prefer a union, like bytes | bytearray, or collections.abc.Buffer. (Contributed by Shantanu Jain in gh-91896.)
• email: Deprecated the isdst parameter in email.utils.localtime(). (Contributed by Alan Williams in gh-72346.)
• importlib.abc deprecated classes:
  • importlib.abc.ResourceReader
  • importlib.abc.Traversable
  • importlib.abc.TraversableResources
    Use importlib.resources.abc classes instead:
  • importlib.resources.abc.Traversable
  • importlib.resources.abc.TraversableResources
    (Contributed by Jason R. Coombs and Hugo van Kemenade in gh-93963.)
• itertools had undocumented, inefficient, historically buggy, and inconsistent support for copy, deepcopy, and pickle operations. This will be removed in 3.14 for a significant reduction in code volume and maintenance burden. (Contributed by Raymond Hettinger in gh-101588.)
• multiprocessing: The default start method will change to a safer one on Linux, BSDs, and other non-macOS POSIX platforms where 'fork' is currently the default (gh-84559). Adding a runtime warning about this was deemed too disruptive as the majority of code is not expected to care. Use theget_context() orset_start_method() APIs to explicitly specify when your code requires 'fork'. See Contexts and start methods.
• pathlib: is_relative_to() andrelative_to(): passing additional arguments is deprecated.
• pkgutil: pkgutil.find_loader() and pkgutil.get_loader()now raise DeprecationWarning; use importlib.util.find_spec() instead. (Contributed by Nikita Sobolev in gh-97850.)
• pty:
  • master_open(): use pty.openpty().
  • slave_open(): use pty.openpty().
• sqlite3:
  • version and version_info.
  • execute() and executemany()if named placeholders are used and_parameters_ is a sequence instead of a dict.
• typing: typing.ByteString, deprecated since Python 3.9, now causes a DeprecationWarning to be emitted when it is used.
• urllib:urllib.parse.Quoter is deprecated: it was not intended to be a public API. (Contributed by Gregory P. Smith in gh-88168.)

Pending removal in Python 3.15¶

• The import system:
  • Setting __cached__ on a module while failing to set __spec__.cachedis deprecated. In Python 3.15, __cached__ will cease to be set or take into consideration by the import system or standard library. (gh-97879)
  • Setting __package__ on a module while failing to set __spec__.parentis deprecated. In Python 3.15, __package__ will cease to be set or take into consideration by the import system or standard library. (gh-97879)
• ctypes:
  • The undocumented ctypes.SetPointerType() function has been deprecated since Python 3.13.
• http.server:
  • The obsolete and rarely used CGIHTTPRequestHandlerhas been deprecated since Python 3.13. No direct replacement exists.Anything is better than CGI to interface a web server with a request handler.
  • The --cgi flag to the python -m http.servercommand-line interface has been deprecated since Python 3.13.
• importlib:
  • load_module() method: use exec_module() instead.
• locale:
  • The getdefaultlocale() function has been deprecated since Python 3.11. Its removal was originally planned for Python 3.13 (gh-90817), but has been postponed to Python 3.15. Use getlocale(), setlocale(), and getencoding() instead. (Contributed by Hugo van Kemenade in gh-111187.)
• pathlib:
  • PurePath.is_reserved()has been deprecated since Python 3.13. Use os.path.isreserved() to detect reserved paths on Windows.
• platform:
  • platform.java_ver() has been deprecated since Python 3.13. This function is only useful for Jython support, has a confusing API, and is largely untested.
• sysconfig:
  • The check_home argument of sysconfig.is_python_build() has been deprecated since Python 3.12.
• threading:
  • RLock() will take no arguments in Python 3.15. Passing any arguments has been deprecated since Python 3.14, as the Python version does not permit any arguments, but the C version allows any number of positional or keyword arguments, ignoring every argument.
• types:
  • types.CodeType: Accessing co_lnotab was deprecated in PEP 626since 3.10 and was planned to be removed in 3.12, but it only got a proper DeprecationWarning in 3.12. May be removed in 3.15. (Contributed by Nikita Sobolev in gh-101866.)
• typing:
  • The undocumented keyword argument syntax for creatingNamedTuple classes (for example, Point = NamedTuple("Point", x=int, y=int)) has been deprecated since Python 3.13. Use the class-based syntax or the functional syntax instead.
  • When using the functional syntax of TypedDicts, failing to pass a value to the fields parameter (TD = TypedDict("TD")) or passing None (TD = TypedDict("TD", None)) has been deprecated since Python 3.13. Use class TD(TypedDict): pass or TD = TypedDict("TD", {})to create a TypedDict with zero field.
  • The typing.no_type_check_decorator() decorator function has been deprecated since Python 3.13. After eight years in the typing module, it has yet to be supported by any major type checker.
• wave:
  • The getmark(), setmark() and getmarkers() methods of the Wave_read and Wave_write classes have been deprecated since Python 3.13.
• zipimport:
  • load_module() has been deprecated since Python 3.10. Use exec_module() instead. (Contributed by Jiahao Li in gh-125746.)

Pending removal in Python 3.16¶

• The import system:
  • Setting __loader__ on a module while failing to set __spec__.loaderis deprecated. In Python 3.16, __loader__ will cease to be set or taken into consideration by the import system or the standard library.
• array:
  • The 'u' format code (wchar_t) has been deprecated in documentation since Python 3.3 and at runtime since Python 3.13. Use the 'w' format code (Py_UCS4) for Unicode characters instead.
• asyncio:
  • asyncio.iscoroutinefunction() is deprecated and will be removed in Python 3.16; use inspect.iscoroutinefunction() instead. (Contributed by Jiahao Li and Kumar Aditya in gh-122875.)
  • asyncio policy system is deprecated and will be removed in Python 3.16. In particular, the following classes and functions are deprecated:
    * asyncio.AbstractEventLoopPolicy
    * asyncio.DefaultEventLoopPolicy
    * asyncio.WindowsSelectorEventLoopPolicy
    * asyncio.WindowsProactorEventLoopPolicy
    * asyncio.get_event_loop_policy()
    * asyncio.set_event_loop_policy()

  Users should use asyncio.run() or asyncio.Runner with_loop_factory_ to use the desired event loop implementation.
  For example, to use asyncio.SelectorEventLoop on Windows:
  import asyncio
  async def main():
  ...
  asyncio.run(main(), loop_factory=asyncio.SelectorEventLoop)
  (Contributed by Kumar Aditya in gh-127949.)

• builtins:
  • Bitwise inversion on boolean types, ~True or ~Falsehas been deprecated since Python 3.12, as it produces surprising and unintuitive results (-2 and -1). Use not x instead for the logical negation of a Boolean. In the rare case that you need the bitwise inversion of the underlying integer, convert to int explicitly (~int(x)).
• functools:
  • Calling the Python implementation of functools.reduce() with _function_or sequence as keyword arguments has been deprecated since Python 3.14.
• logging:
  Support for custom logging handlers with the strm argument is deprecated and scheduled for removal in Python 3.16. Define handlers with the _stream_argument instead. (Contributed by Mariusz Felisiak in gh-115032.)
• mimetypes:
  • Valid extensions start with a ‘.’ or are empty formimetypes.MimeTypes.add_type(). Undotted extensions are deprecated and will raise a ValueError in Python 3.16. (Contributed by Hugo van Kemenade in gh-75223.)
• shutil:
  • The ExecError exception has been deprecated since Python 3.14. It has not been used by any function in shutil since Python 3.4, and is now an alias of RuntimeError.
• symtable:
  • The Class.get_methods method has been deprecated since Python 3.14.
• sys:
  • The _enablelegacywindowsfsencoding() function has been deprecated since Python 3.13. Use the PYTHONLEGACYWINDOWSFSENCODING environment variable instead.
• sysconfig:
  • The sysconfig.expand_makefile_vars() function has been deprecated since Python 3.14. Use the vars argument of sysconfig.get_paths() instead.
• tarfile:
  • The undocumented and unused TarFile.tarfile attribute has been deprecated since Python 3.13.

Pending removal in Python 3.17¶

• typing:
  • Before Python 3.14, old-style unions were implemented using the private classtyping._UnionGenericAlias. This class is no longer needed for the implementation, but it has been retained for backward compatibility, with removal scheduled for Python 3.17. Users should use documented introspection helpers like typing.get_origin()and typing.get_args() instead of relying on private implementation details.

Pending removal in future versions¶

The following APIs will be removed in the future, although there is currently no date scheduled for their removal.

• argparse:
  • Nesting argument groups and nesting mutually exclusive groups are deprecated.
  • Passing the undocumented keyword argument prefix_chars toadd_argument_group() is now deprecated.
  • The argparse.FileType type converter is deprecated.
• builtins:
  • bool(NotImplemented).
  • Generators: throw(type, exc, tb) and athrow(type, exc, tb)signature is deprecated: use throw(exc) and athrow(exc) instead, the single argument signature.
  • 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 keywordsand, else, for, if,in, is and or. In a future release it will be changed to a syntax error. (gh-87999)
  • Support for __index__() and __int__() method returning non-int type: these methods will be required to return an instance of a strict subclass ofint.
  • Support for __float__() method returning a strict subclass offloat: these methods will be required to return an instance offloat.
  • Support for __complex__() method returning a strict subclass ofcomplex: these methods will be required to return an instance ofcomplex.
  • Delegation of int() to __trunc__() method.
  • Passing a complex number as the real or imag argument in thecomplex() constructor is now deprecated; it should only be passed as a single positional argument. (Contributed by Serhiy Storchaka in gh-109218.)
• calendar: calendar.January and calendar.February constants are deprecated and replaced by calendar.JANUARY andcalendar.FEBRUARY. (Contributed by Prince Roshan in gh-103636.)
• codecs: use open() instead of codecs.open(). (gh-133038)
• codeobject.co_lnotab: use the codeobject.co_lines() method instead.
• datetime:
  • utcnow(): use datetime.datetime.now(tz=datetime.UTC).
  • utcfromtimestamp(): use datetime.datetime.fromtimestamp(timestamp, tz=datetime.UTC).
• gettext: Plural value must be an integer.
• importlib:
  • cache_from_source() debug_override parameter is deprecated: use the optimization parameter instead.
• importlib.metadata:
  • EntryPoints tuple interface.
  • Implicit None on return values.
• logging: the warn() method has been deprecated since Python 3.3, use warning() instead.
• mailbox: Use of StringIO input and text mode is deprecated, use BytesIO and binary mode instead.
• os: Calling os.register_at_fork() in multi-threaded process.
• pydoc.ErrorDuringImport: A tuple value for exc_info parameter is deprecated, use an exception instance.
• re: 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.)
• sre_compile, sre_constants and sre_parse modules.
• shutil: rmtree()’s onerror parameter is deprecated in Python 3.12; use the onexc parameter instead.
• ssl options and protocols:
  • ssl.SSLContext without protocol argument is deprecated.
  • ssl.SSLContext: set_npn_protocols() andselected_npn_protocol() are deprecated: use ALPN instead.
  • ssl.OP_NO_SSL* options
  • ssl.OP_NO_TLS* options
  • ssl.PROTOCOL_SSLv3
  • ssl.PROTOCOL_TLS
  • ssl.PROTOCOL_TLSv1
  • ssl.PROTOCOL_TLSv1_1
  • ssl.PROTOCOL_TLSv1_2
  • ssl.TLSVersion.SSLv3
  • ssl.TLSVersion.TLSv1
  • ssl.TLSVersion.TLSv1_1
• threading methods:
  • threading.Condition.notifyAll(): use notify_all().
  • threading.Event.isSet(): use is_set().
  • threading.Thread.isDaemon(), threading.Thread.setDaemon(): use threading.Thread.daemon attribute.
  • threading.Thread.getName(), threading.Thread.setName(): use threading.Thread.name attribute.
  • threading.currentThread(): use threading.current_thread().
  • threading.activeCount(): use threading.active_count().
• typing.Text (gh-92332).
• The internal class typing._UnionGenericAlias is no longer used to implementtyping.Union. To preserve compatibility with users using this private class, a compatibility shim will be provided until at least Python 3.17. (Contributed by Jelle Zijlstra in gh-105499.)
• unittest.IsolatedAsyncioTestCase: it is deprecated to return a value that is not None from a test case.
• urllib.parse deprecated functions: urlparse() instead
  • splitattr()
  • splithost()
  • splitnport()
  • splitpasswd()
  • splitport()
  • splitquery()
  • splittag()
  • splittype()
  • splituser()
  • splitvalue()
  • to_bytes()
• wsgiref: SimpleHandler.stdout.write() should not do partial writes.
• xml.etree.ElementTree: Testing the truth value of anElement is deprecated. In a future release it will always return True. Prefer explicit len(elem) orelem is not None tests instead.
• sys._clear_type_cache() is deprecated: use sys._clear_internal_caches() instead.

CPython Bytecode Changes¶

• The oparg of YIELD_VALUE is now1 if the yield is part of a yield-from or await, and 0 otherwise. The oparg of RESUME was changed to add a bit indicating if the except-depth is 1, which is needed to optimize closing of generators. (Contributed by Irit Katriel in gh-111354.)

C API Changes¶

New Features¶

• Add the PyMonitoring C APIfor generating PEP 669 monitoring events:
  • PyMonitoringState
  • PyMonitoring_FirePyStartEvent()
  • PyMonitoring_FirePyResumeEvent()
  • PyMonitoring_FirePyReturnEvent()
  • PyMonitoring_FirePyYieldEvent()
  • PyMonitoring_FireCallEvent()
  • PyMonitoring_FireLineEvent()
  • PyMonitoring_FireJumpEvent()
  • PyMonitoring_FireBranchEvent
  • PyMonitoring_FireCReturnEvent()
  • PyMonitoring_FirePyThrowEvent()
  • PyMonitoring_FireRaiseEvent()
  • PyMonitoring_FireCRaiseEvent()
  • PyMonitoring_FireReraiseEvent()
  • PyMonitoring_FireExceptionHandledEvent()
  • PyMonitoring_FirePyUnwindEvent()
  • PyMonitoring_FireStopIterationEvent()
  • PyMonitoring_EnterScope()
  • PyMonitoring_ExitScope()
    (Contributed by Irit Katriel in gh-111997).
• Add PyMutex, a lightweight mutex that occupies a single byte, and the new PyMutex_Lock() and PyMutex_Unlock() functions.PyMutex_Lock() will release the GIL (if currently held) if the operation needs to block. (Contributed by Sam Gross in gh-108724.)
• Add the PyTime C API to provide access to system clocks:
  • PyTime_t.
  • PyTime_MIN and PyTime_MAX.
  • PyTime_AsSecondsDouble().
  • PyTime_Monotonic().
  • PyTime_MonotonicRaw().
  • PyTime_PerfCounter().
  • PyTime_PerfCounterRaw().
  • PyTime_Time().
  • PyTime_TimeRaw().
    (Contributed by Victor Stinner and Petr Viktorin in gh-110850.)
• Add the PyDict_ContainsString() function with the same behavior as PyDict_Contains(), but key is specified as a const char* UTF-8 encoded bytes string, rather than a PyObject*. (Contributed by Victor Stinner in gh-108314.)
• Add the PyDict_GetItemRef() and PyDict_GetItemStringRef()functions, which behave similarly to PyDict_GetItemWithError(), but return a strong reference instead of a borrowed reference. Moreover, these functions return -1 on error, removing the need to check PyErr_Occurred(). (Contributed by Victor Stinner in gh-106004.)
• Add the PyDict_SetDefaultRef() function, which behaves similarly to PyDict_SetDefault(), but returns a strong reference instead of a borrowed reference. This function returns -1 on error,0 on insertion, and 1 if the key was already present in the dictionary. (Contributed by Sam Gross in gh-112066.)
• Add the PyDict_Pop() and PyDict_PopString() functions to remove a key from a dictionary and optionally return the removed value. This is similar to dict.pop(), though there is no default value, and KeyError is not raised for missing keys. (Contributed by Stefan Behnel and Victor Stinner in gh-111262.)
• Add the PyMapping_GetOptionalItem()and PyMapping_GetOptionalItemString() functions as alternatives to PyObject_GetItem()and PyMapping_GetItemString() respectively. The new functions do not raise KeyErrorif the requested key is missing from the mapping. These variants are more convenient and faster if a missing key should not be treated as a failure. (Contributed by Serhiy Storchaka in gh-106307.)
• Add the PyObject_GetOptionalAttr()and PyObject_GetOptionalAttrString() functions as alternatives to PyObject_GetAttr()and PyObject_GetAttrString() respectively. The new functions do not raise AttributeErrorif the requested attribute is not found on the object. These variants are more convenient and faster if the missing attribute should not be treated as a failure. (Contributed by Serhiy Storchaka in gh-106521.)
• Add the PyErr_FormatUnraisable() function as an extension to PyErr_WriteUnraisable()that allows customizing the warning message. (Contributed by Serhiy Storchaka in gh-108082.)
• Add new functions that return a strong reference instead of a borrowed reference for frame locals, globals, and builtins, as part of PEP 667:
  • PyEval_GetFrameBuiltins() replaces PyEval_GetBuiltins()
  • PyEval_GetFrameGlobals() replaces PyEval_GetGlobals()
  • PyEval_GetFrameLocals() replaces PyEval_GetLocals()
    (Contributed by Mark Shannon and Tian Gao in gh-74929.)
• Add the Py_GetConstant() and Py_GetConstantBorrowed()functions to get strongor borrowed references to constants. For example, Py_GetConstant(Py_CONSTANT_ZERO) returns a strong reference to the constant zero. (Contributed by Victor Stinner in gh-115754.)
• Add the PyImport_AddModuleRef() function as a replacement for PyImport_AddModule()that returns a strong reference instead of a borrowed reference. (Contributed by Victor Stinner in gh-105922.)
• Add the Py_IsFinalizing() function to check whether the main Python interpreter isshutting down. (Contributed by Victor Stinner in gh-108014.)
• Add the PyList_GetItemRef() function as a replacement for PyList_GetItem()that returns a strong reference instead of a borrowed reference. (Contributed by Sam Gross in gh-114329.)
• Add the PyList_Extend() and PyList_Clear() functions, mirroring the Python list.extend() and list.clear() methods. (Contributed by Victor Stinner in gh-111138.)
• Add the PyLong_AsInt() function. It behaves similarly to PyLong_AsLong(), but stores the result in a C int instead of a C long. (Contributed by Victor Stinner in gh-108014.)
• Add the PyLong_AsNativeBytes(), PyLong_FromNativeBytes(), and PyLong_FromUnsignedNativeBytes() functions to simplify converting between native integer types and Python int objects. (Contributed by Steve Dower in gh-111140.)
• Add PyModule_Add() function, which is similar toPyModule_AddObjectRef() and PyModule_AddObject(), but always steals a reference to the value. (Contributed by Serhiy Storchaka in gh-86493.)
• Add the PyObject_GenericHash() function that implements the default hashing function of a Python object. (Contributed by Serhiy Storchaka in gh-113024.)
• Add the Py_HashPointer() function to hash a raw pointer. (Contributed by Victor Stinner in gh-111545.)
• Add the PyObject_VisitManagedDict() andPyObject_ClearManagedDict() functions. which must be called by the traverse and clear functions of a type using the Py_TPFLAGS_MANAGED_DICT flag. The pythoncapi-compat project can be used to use these functions with Python 3.11 and 3.12. (Contributed by Victor Stinner in gh-107073.)
• Add the PyRefTracer_SetTracer()and PyRefTracer_GetTracer() functions, which enable tracking object creation and destruction in the same way that the tracemalloc module does. (Contributed by Pablo Galindo in gh-93502.)
• Add the PySys_AuditTuple() function as an alternative to PySys_Audit()that takes event arguments as a Python tuple object. (Contributed by Victor Stinner in gh-85283.)
• Add the PyThreadState_GetUnchecked() function as an alternative to PyThreadState_Get()that doesn’t kill the process with a fatal error if it is NULL. The caller is responsible for checking if the result is NULL. (Contributed by Victor Stinner in gh-108867.)
• Add the PyType_GetFullyQualifiedName() function to get the type’s fully qualified name. The module name is prepended if type.__module__ is a string and is not equal to either 'builtins' or '__main__'. (Contributed by Victor Stinner in gh-111696.)
• Add the PyType_GetModuleName() function to get the type’s module name. This is equivalent to getting thetype.__module__ attribute. (Contributed by Eric Snow and Victor Stinner in gh-111696.)
• Add the PyUnicode_EqualToUTF8AndSize()and PyUnicode_EqualToUTF8() functions to compare a Unicode object with a const char* UTF-8 encoded string and 1 if they are equal or 0 otherwise. These functions do not raise exceptions. (Contributed by Serhiy Storchaka in gh-110289.)
• Add the PyWeakref_GetRef() function as an alternative to PyWeakref_GetObject()that returns a strong referenceor NULL if the referent is no longer live. (Contributed by Victor Stinner in gh-105927.)
• Add fixed variants of functions which silently ignore errors:
  • PyObject_HasAttrWithError() replaces PyObject_HasAttr().
  • PyObject_HasAttrStringWithError()replaces PyObject_HasAttrString().
  • PyMapping_HasKeyWithError() replaces PyMapping_HasKey().
  • PyMapping_HasKeyStringWithError()replaces PyMapping_HasKeyString().
    The new functions return -1 for errors and the standard 1 for true and 0 for false.
    (Contributed by Serhiy Storchaka in gh-108511.)

Changed C APIs¶

• The keywords parameter of PyArg_ParseTupleAndKeywords()and PyArg_VaParseTupleAndKeywords()now has type char *const* in C and const char *const* in C++, instead of char**. In C++, this makes these functions compatible with arguments of type const char *const*, const char**, or char *const* without an explicit type cast. In C, the functions only support arguments of type char *const*. This can be overridden with the PY_CXX_CONST macro. (Contributed by Serhiy Storchaka in gh-65210.)
• PyArg_ParseTupleAndKeywords() now supports non-ASCII keyword parameter names. (Contributed by Serhiy Storchaka in gh-110815.)
• The PyCode_GetFirstFree() function is now unstable API and is now named PyUnstable_Code_GetFirstFree(). (Contributed by Bogdan Romanyuk in gh-115781.)
• The PyDict_GetItem(), PyDict_GetItemString(),PyMapping_HasKey(), PyMapping_HasKeyString(),PyObject_HasAttr(), PyObject_HasAttrString(), and PySys_GetObject() functions, each of which clears all errors which occurred when calling them now reports these errors using sys.unraisablehook(). You may replace them with other functions as recommended in the documentation. (Contributed by Serhiy Storchaka in gh-106672.)
• Add support for the %T, %#T, %N and %#N formats to PyUnicode_FromFormat():
  • %T: Get the fully qualified name of an object type
  • %#T: As above, but use a colon as the separator
  • %N: Get the fully qualified name of a type
  • %#N: As above, but use a colon as the separator
    See PEP 737 for more information. (Contributed by Victor Stinner in gh-111696.)
• You no longer have to define the PY_SSIZE_T_CLEAN macro before including Python.h when using # formats informat codes. APIs accepting the format codes always use Py_ssize_t for # formats. (Contributed by Inada Naoki in gh-104922.)
• If Python is built in debug modeor with assertions,PyTuple_SET_ITEM() and PyList_SET_ITEM()now check the index argument with an assertion. (Contributed by Victor Stinner in gh-106168.)

Limited C API Changes¶

• The following functions are now included in the Limited C API:
  • PyMem_RawMalloc()
  • PyMem_RawCalloc()
  • PyMem_RawRealloc()
  • PyMem_RawFree()
  • PySys_Audit()
  • PySys_AuditTuple()
  • PyType_GetModuleByDef()
    (Contributed by Victor Stinner in gh-85283, gh-85283, and gh-116936.)
• Python built with --with-trace-refs (tracing references) now supports the Limited API. (Contributed by Victor Stinner in gh-108634.)

Removed C APIs¶

• Remove several functions, macros, variables, etc with names prefixed by _Py or _PY (which are considered private). If your project is affected by one of these removals and you believe that the removed API should remain available, please open a new issue to request a public C API and add cc: @vstinner to the issue to notify Victor Stinner. (Contributed by Victor Stinner in gh-106320.)
• Remove old buffer protocols deprecated in Python 3.0. Use Buffer Protocol instead.
  • PyObject_CheckReadBuffer(): Use PyObject_CheckBuffer() to test whether the object supports the buffer protocol. Note that PyObject_CheckBuffer() doesn’t guarantee that PyObject_GetBuffer() will succeed. To test if the object is actually readable, see the next example of PyObject_GetBuffer().
  • PyObject_AsCharBuffer(), PyObject_AsReadBuffer(): Use PyObject_GetBuffer() and PyBuffer_Release() instead:
    Py_buffer view;
    if (PyObject_GetBuffer(obj, &view, PyBUF_SIMPLE) < 0) {
    return NULL;
    }
    // Use view.buf and view.len to read from the buffer.
    // You may need to cast buf as (const char*)view.buf.
    PyBuffer_Release(&view);
  • PyObject_AsWriteBuffer(): Use PyObject_GetBuffer() and PyBuffer_Release() instead:
    Py_buffer view;
    if (PyObject_GetBuffer(obj, &view, PyBUF_WRITABLE) < 0) {
    return NULL;
    }
    // Use view.buf and view.len to write to the buffer.
    PyBuffer_Release(&view);
    (Contributed by Inada Naoki in gh-85275.)
• Remove various functions deprecated in Python 3.9:
  • PyEval_CallObject(), PyEval_CallObjectWithKeywords(): Use PyObject_CallNoArgs() or PyObject_Call() instead.
    Warning
    In PyObject_Call(), positional arguments must be a tupleand must not be NULL, and keyword arguments must be a dict or NULL, whereas the removed functions checked argument types and accepted NULL positional and keyword arguments. To replace PyEval_CallObjectWithKeywords(func, NULL, kwargs) withPyObject_Call(), pass an empty tuple as positional arguments usingPyTuple_New(0).
  • PyEval_CallFunction(): Use PyObject_CallFunction() instead.
  • PyEval_CallMethod(): Use PyObject_CallMethod() instead.
  • PyCFunction_Call(): Use PyObject_Call() instead.
    (Contributed by Victor Stinner in gh-105107.)
• Remove the following old functions to configure the Python initialization, deprecated in Python 3.11:
  • PySys_AddWarnOptionUnicode(): Use PyConfig.warnoptions instead.
  • PySys_AddWarnOption(): Use PyConfig.warnoptions instead.
  • PySys_AddXOption(): Use PyConfig.xoptions instead.
  • PySys_HasWarnOptions(): Use PyConfig.xoptions instead.
  • PySys_SetPath(): Set PyConfig.module_search_paths instead.
  • Py_SetPath(): Set PyConfig.module_search_paths instead.
  • Py_SetStandardStreamEncoding(): Set PyConfig.stdio_encoding instead, and set also maybe PyConfig.legacy_windows_stdio (on Windows).
  • _Py_SetProgramFullPath(): Set PyConfig.executable instead.
    Use the new PyConfig API of the Python Initialization Configuration instead (PEP 587), added to Python 3.8. (Contributed by Victor Stinner in gh-105145.)
• Remove PyEval_AcquireLock() and PyEval_ReleaseLock() functions, deprecated in Python 3.2. They didn’t update the current thread state. They can be replaced with:
  • PyEval_SaveThread() and PyEval_RestoreThread();
  • low-level PyEval_AcquireThread() and PyEval_RestoreThread();
  • or PyGILState_Ensure() and PyGILState_Release().
    (Contributed by Victor Stinner in gh-105182.)
• Remove the PyEval_ThreadsInitialized() function, deprecated in Python 3.9. Since Python 3.7, Py_Initialize() always creates the GIL: calling PyEval_InitThreads() does nothing andPyEval_ThreadsInitialized() always returns non-zero. (Contributed by Victor Stinner in gh-105182.)
• Remove the _PyInterpreterState_Get() alias toPyInterpreterState_Get()which was kept for backward compatibility with Python 3.8. The pythoncapi-compat project can be used to getPyInterpreterState_Get() on Python 3.8 and older. (Contributed by Victor Stinner in gh-106320.)
• Remove the private _PyObject_FastCall() function: use PyObject_Vectorcall() which is available since Python 3.8 (PEP 590). (Contributed by Victor Stinner in gh-106023.)
• Remove the cpython/pytime.h header file, which only contained private functions. (Contributed by Victor Stinner in gh-106316.)
• Remove the undocumented PY_TIMEOUT_MAX constant from the limited C API. (Contributed by Victor Stinner in gh-110014.)
• Remove the old trashcan macros Py_TRASHCAN_SAFE_BEGINand Py_TRASHCAN_SAFE_END. Replace both with the new macros Py_TRASHCAN_BEGINand Py_TRASHCAN_END. (Contributed by Irit Katriel in gh-105111.)

Deprecated C APIs¶

• Deprecate old Python initialization functions:
  • PySys_ResetWarnOptions(): Clear sys.warnoptions and warnings.filters instead.
  • Py_GetExecPrefix(): Get sys.exec_prefix instead.
  • Py_GetPath(): Get sys.path instead.
  • Py_GetPrefix(): Get sys.prefix instead.
  • Py_GetProgramFullPath(): Get sys.executable instead.
  • Py_GetProgramName(): Get sys.executable instead.
  • Py_GetPythonHome(): Get PyConfig.homeor the PYTHONHOME environment variable instead.
    (Contributed by Victor Stinner in gh-105145.)
• Soft deprecate thePyEval_GetBuiltins(), PyEval_GetGlobals(), and PyEval_GetLocals() functions, which return a borrowed reference. (Soft deprecated as part of PEP 667.)
• Deprecate the PyImport_ImportModuleNoBlock() function, which is just an alias to PyImport_ImportModule() since Python 3.3. (Contributed by Victor Stinner in gh-105396.)
• Soft deprecate thePyModule_AddObject() function. It should be replaced with PyModule_Add()or PyModule_AddObjectRef(). (Contributed by Serhiy Storchaka in gh-86493.)
• Deprecate the old Py_UNICODE and PY_UNICODE_TYPE types and the Py_UNICODE_WIDE define. Use the wchar_t type directly instead. Since Python 3.3, Py_UNICODE and PY_UNICODE_TYPEare just aliases to wchar_t. (Contributed by Victor Stinner in gh-105156.)
• Deprecate the PyWeakref_GetObject() andPyWeakref_GET_OBJECT() functions, which return a borrowed reference. Replace them with the new PyWeakref_GetRef() function, which returns a strong reference. The pythoncapi-compat project can be used to getPyWeakref_GetRef() on Python 3.12 and older. (Contributed by Victor Stinner in gh-105927.)

Pending removal in Python 3.14¶

• The ma_version_tag field in PyDictObject for extension modules (PEP 699; gh-101193).
• Creating immutable types with mutable bases (gh-95388).

Pending removal in Python 3.15¶

• The bundled copy of libmpdecimal.
• The PyImport_ImportModuleNoBlock(): Use PyImport_ImportModule() instead.
• PyWeakref_GetObject() and PyWeakref_GET_OBJECT(): Use PyWeakref_GetRef() instead. The pythoncapi-compat project can be used to getPyWeakref_GetRef() on Python 3.12 and older.
• Py_UNICODE type and the Py_UNICODE_WIDE macro: Use wchar_t instead.
• PyUnicode_AsDecodedObject(): Use PyCodec_Decode() instead.
• PyUnicode_AsDecodedUnicode(): Use PyCodec_Decode() instead; Note that some codecs (for example, “base64”) may return a type other than str, such as bytes.
• PyUnicode_AsEncodedObject(): Use PyCodec_Encode() instead.
• PyUnicode_AsEncodedUnicode(): Use PyCodec_Encode() instead; Note that some codecs (for example, “base64”) may return a type other than bytes, such as str.
• Python initialization functions, deprecated in Python 3.13:
  • Py_GetPath(): Use PyConfig_Get("module_search_paths")(sys.path) instead.
  • Py_GetPrefix(): Use PyConfig_Get("base_prefix")(sys.base_prefix) instead. Use PyConfig_Get("prefix") (sys.prefix) if virtual environments need to be handled.
  • Py_GetExecPrefix(): Use PyConfig_Get("base_exec_prefix")(sys.base_exec_prefix) instead. UsePyConfig_Get("exec_prefix")(sys.exec_prefix) if virtual environments need to be handled.
  • Py_GetProgramFullPath(): Use PyConfig_Get("executable")(sys.executable) instead.
  • Py_GetProgramName(): Use PyConfig_Get("executable")(sys.executable) instead.
  • Py_GetPythonHome(): Use PyConfig_Get("home") or thePYTHONHOME environment variable instead.
    The pythoncapi-compat project can be used to getPyConfig_Get() on Python 3.13 and older.
• Functions to configure Python’s initialization, deprecated in Python 3.11:
  • PySys_SetArgvEx(): Set PyConfig.argv instead.
  • PySys_SetArgv(): Set PyConfig.argv instead.
  • Py_SetProgramName(): Set PyConfig.program_name instead.
  • Py_SetPythonHome(): Set PyConfig.home instead.
  • PySys_ResetWarnOptions(): Clear sys.warnoptions and warnings.filters instead.
    The Py_InitializeFromConfig() API should be used withPyConfig instead.
• Global configuration variables:
  • Py_DebugFlag: Use PyConfig.parser_debug orPyConfig_Get("parser_debug") instead.
  • Py_VerboseFlag: Use PyConfig.verbose orPyConfig_Get("verbose") instead.
  • Py_QuietFlag: Use PyConfig.quiet orPyConfig_Get("quiet") instead.
  • Py_InteractiveFlag: Use PyConfig.interactive orPyConfig_Get("interactive") instead.
  • Py_InspectFlag: Use PyConfig.inspect orPyConfig_Get("inspect") instead.
  • Py_OptimizeFlag: Use PyConfig.optimization_level orPyConfig_Get("optimization_level") instead.
  • Py_NoSiteFlag: Use PyConfig.site_import orPyConfig_Get("site_import") instead.
  • Py_BytesWarningFlag: Use PyConfig.bytes_warning orPyConfig_Get("bytes_warning") instead.
  • Py_FrozenFlag: Use PyConfig.pathconfig_warnings orPyConfig_Get("pathconfig_warnings") instead.
  • Py_IgnoreEnvironmentFlag: Use PyConfig.use_environment orPyConfig_Get("use_environment") instead.
  • Py_DontWriteBytecodeFlag: Use PyConfig.write_bytecode orPyConfig_Get("write_bytecode") instead.
  • Py_NoUserSiteDirectory: Use PyConfig.user_site_directory orPyConfig_Get("user_site_directory") instead.
  • Py_UnbufferedStdioFlag: Use PyConfig.buffered_stdio orPyConfig_Get("buffered_stdio") instead.
  • Py_HashRandomizationFlag: Use PyConfig.use_hash_seedand PyConfig.hash_seed orPyConfig_Get("hash_seed") instead.
  • Py_IsolatedFlag: Use PyConfig.isolated orPyConfig_Get("isolated") instead.
  • Py_LegacyWindowsFSEncodingFlag: Use PyPreConfig.legacy_windows_fs_encoding orPyConfig_Get("legacy_windows_fs_encoding") instead.
  • Py_LegacyWindowsStdioFlag: Use PyConfig.legacy_windows_stdio orPyConfig_Get("legacy_windows_stdio") instead.
  • Py_FileSystemDefaultEncoding, Py_HasFileSystemDefaultEncoding: Use PyConfig.filesystem_encoding orPyConfig_Get("filesystem_encoding") instead.
  • Py_FileSystemDefaultEncodeErrors: Use PyConfig.filesystem_errors orPyConfig_Get("filesystem_errors") instead.
  • Py_UTF8Mode: Use PyPreConfig.utf8_mode orPyConfig_Get("utf8_mode") instead. (see Py_PreInitialize())
    The Py_InitializeFromConfig() API should be used withPyConfig to set these options. Or PyConfig_Get() can be used to get these options at runtime.

Pending removal in Python 3.18¶

• Deprecated private functions (gh-128863):
  • _PyBytes_Join(): use PyBytes_Join().
  • _PyDict_GetItemStringWithError(): use PyDict_GetItemStringRef().
  • _PyDict_Pop(): PyDict_Pop().
  • _PyLong_Sign(): use PyLong_GetSign().
  • _PyLong_FromDigits() and _PyLong_New(): use PyLongWriter_Create().
  • _PyThreadState_UncheckedGet(): use PyThreadState_GetUnchecked().
  • _PyUnicode_AsString(): use PyUnicode_AsUTF8().
  • _PyUnicodeWriter_Init(): replace _PyUnicodeWriter_Init(&writer) withwriter = PyUnicodeWriter_Create(0).
  • _PyUnicodeWriter_Finish(): replace _PyUnicodeWriter_Finish(&writer) withPyUnicodeWriter_Finish(writer).
  • _PyUnicodeWriter_Dealloc(): replace _PyUnicodeWriter_Dealloc(&writer) withPyUnicodeWriter_Discard(writer).
  • _PyUnicodeWriter_WriteChar(): replace _PyUnicodeWriter_WriteChar(&writer, ch) withPyUnicodeWriter_WriteChar(writer, ch).
  • _PyUnicodeWriter_WriteStr(): replace _PyUnicodeWriter_WriteStr(&writer, str) withPyUnicodeWriter_WriteStr(writer, str).
  • _PyUnicodeWriter_WriteSubstring(): replace _PyUnicodeWriter_WriteSubstring(&writer, str, start, end) withPyUnicodeWriter_WriteSubstring(writer, str, start, end).
  • _PyUnicodeWriter_WriteASCIIString(): replace _PyUnicodeWriter_WriteASCIIString(&writer, str) withPyUnicodeWriter_WriteUTF8(writer, str).
  • _PyUnicodeWriter_WriteLatin1String(): replace _PyUnicodeWriter_WriteLatin1String(&writer, str) withPyUnicodeWriter_WriteUTF8(writer, str).
  • _PyUnicodeWriter_Prepare(): (no replacement).
  • _PyUnicodeWriter_PrepareKind(): (no replacement).
  • _Py_HashPointer(): use Py_HashPointer().
  • _Py_fopen_obj(): use Py_fopen().
    The pythoncapi-compat project can be used to get these new public functions on Python 3.13 and older.

Pending removal in future versions¶

The following APIs are deprecated and will be removed, although there is currently no date scheduled for their removal.

• Py_TPFLAGS_HAVE_FINALIZE: Unneeded since Python 3.8.
• PyErr_Fetch(): Use PyErr_GetRaisedException() instead.
• PyErr_NormalizeException(): Use PyErr_GetRaisedException() instead.
• PyErr_Restore(): Use PyErr_SetRaisedException() instead.
• PyModule_GetFilename(): Use PyModule_GetFilenameObject() instead.
• PyOS_AfterFork(): Use PyOS_AfterFork_Child() instead.
• PySlice_GetIndicesEx(): Use PySlice_Unpack() and PySlice_AdjustIndices() instead.
• PyUnicode_READY(): Unneeded since Python 3.12
• PyErr_Display(): Use PyErr_DisplayException() instead.
• _PyErr_ChainExceptions(): Use _PyErr_ChainExceptions1() instead.
• PyBytesObject.ob_shash member: call PyObject_Hash() instead.
• Thread Local Storage (TLS) API:
  • PyThread_create_key(): Use PyThread_tss_alloc() instead.
  • PyThread_delete_key(): Use PyThread_tss_free() instead.
  • PyThread_set_key_value(): Use PyThread_tss_set() instead.
  • PyThread_get_key_value(): Use PyThread_tss_get() instead.
  • PyThread_delete_key_value(): Use PyThread_tss_delete() instead.
  • PyThread_ReInitTLS(): Unneeded since Python 3.7.

Build Changes¶

• arm64-apple-ios and arm64-apple-ios-simulator are both now PEP 11 tier 3 platforms. (PEP 730 written and implementation contributed by Russell Keith-Magee in gh-114099.)
• aarch64-linux-android and x86_64-linux-android are both now PEP 11 tier 3 platforms. (PEP 738 written and implementation contributed by Malcolm Smith in gh-116622.)
• wasm32-wasi is now a PEP 11 tier 2 platform. (Contributed by Brett Cannon in gh-115192.)
• wasm32-emscripten is no longer a PEP 11 supported platform. (Contributed by Brett Cannon in gh-115192.)
• Building CPython now requires a compiler with support for the C11 atomic library, GCC built-in atomic functions, or MSVC interlocked intrinsics.
• Autoconf 2.71 and aclocal 1.16.5 are now required to regenerate the configure script. (Contributed by Christian Heimes in gh-89886 and by Victor Stinner in gh-112090.)
• SQLite 3.15.2 or newer is required to build the sqlite3 extension module. (Contributed by Erlend Aasland in gh-105875.)
• CPython now bundles the mimalloc library by default. It is licensed under the MIT license; see mimalloc license. The bundled mimalloc has custom changes, see gh-113141 for details. (Contributed by Dino Viehland in gh-109914.)
• The configure option --with-system-libmpdecnow defaults to yes. The bundled copy of libmpdecimal will be removed in Python 3.15.
• Python built with configure --with-trace-refs(tracing references) is now ABI compatible with the Python release build and debug build. (Contributed by Victor Stinner in gh-108634.)
• On POSIX systems, the pkg-config (.pc) filenames now include the ABI flags. For example, the free-threaded build generates python-3.13t.pcand the debug build generates python-3.13d.pc.
• The errno, fcntl, grp, md5, pwd, resource,termios, winsound,_ctypes_test, _multiprocessing.posixshmem, _scproxy, _stat,_statistics, _testconsole, _testimportmultiple and _uuidC extensions are now built with the limited C API. (Contributed by Victor Stinner in gh-85283.)

Porting to Python 3.13¶

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

Changes in the Python API¶

• PEP 667 introduces several changes to the semantics of locals() and f_locals:
  • Calling locals() in an optimized scope now produces an independent snapshot on each call, and hence no longer implicitly updates previously returned references. Obtaining the legacy CPython behavior now requires explicit calls to update the initially returned dictionary with the results of subsequent calls to locals(). Code execution functions that implicitly target locals() (such as exec and eval) must be passed an explicit namespace to access their results in an optimized scope. (Changed as part of PEP 667.)
  • Calling locals() from a comprehension at module or class scope (including via exec or eval) once more behaves as if the comprehension were running as an independent nested function (i.e. the local variables from the containing scope are not included). In Python 3.12, this had changed to include the local variables from the containing scope when implementingPEP 709. (Changed as part of PEP 667.)
  • Accessing FrameType.f_locals in anoptimized scope now returns a write-through proxy rather than a snapshot that gets updated at ill-specified times. If a snapshot is desired, it must be created explicitly with dict or the proxy’s .copy() method. (Changed as part of PEP 667.)
• functools.partial now emits a FutureWarningwhen used as a method. The behavior will change in future Python versions. Wrap it in staticmethod() if you want to preserve the old behavior. (Contributed by Serhiy Storchaka in gh-121027.)
• An OSError is now raised by getpass.getuser()for any failure to retrieve a username, instead of ImportError on non-Unix platforms or KeyError on Unix platforms where the password database is empty.
• The value of the mode attribute of gzip.GzipFileis now a string ('rb' or 'wb') instead of an integer (1 or 2). The value of the mode attribute of the readable file-like object returned by zipfile.ZipFile.open() is now 'rb' instead of 'r'. (Contributed by Serhiy Storchaka in gh-115961.)
• mailbox.Maildir now ignores files with a leading dot (.). (Contributed by Zackery Spytz in gh-65559.)
• pathlib.Path.glob() and rglob() now return both files and directories if a pattern that ends with “**” is given, rather than directories only. Add a trailing slash to keep the previous behavior and only match directories.
• The threading module now expects the _thread module to have an _is_main_interpreter() function. This function takes no arguments and returns Trueif the current interpreter is the main interpreter.
  Any library or application that provides a custom _thread module must provide _is_main_interpreter(), just like the module’s other “private” attributes. (gh-112826.)

Changes in the C API¶

• Python.h no longer includes the <ieeefp.h> standard header. It was included for the finite() function which is now provided by the<math.h> header. It should now be included explicitly if needed. Remove also the HAVE_IEEEFP_H macro. (Contributed by Victor Stinner in gh-108765.)
• Python.h no longer includes these standard header files: <time.h>,<sys/select.h> and <sys/time.h>. If needed, they should now be included explicitly. For example, <time.h> provides the clock() andgmtime() functions, <sys/select.h> provides the select()function, and <sys/time.h> provides the futimes(), gettimeofday()and setitimer() functions. (Contributed by Victor Stinner in gh-108765.)
• On Windows, Python.h no longer includes the <stddef.h> standard header file. If needed, it should now be included explicitly. For example, it provides offsetof() function, and size_t and ptrdiff_t types. Including <stddef.h> explicitly was already needed by all other platforms, the HAVE_STDDEF_H macro is only defined on Windows. (Contributed by Victor Stinner in gh-108765.)
• If the Py_LIMITED_API macro is defined, Py_BUILD_CORE,Py_BUILD_CORE_BUILTIN and Py_BUILD_CORE_MODULE macros are now undefined by <Python.h>. (Contributed by Victor Stinner in gh-85283.)
• The old trashcan macros Py_TRASHCAN_SAFE_BEGIN and Py_TRASHCAN_SAFE_ENDwere removed. They should be replaced by the new macros Py_TRASHCAN_BEGINand Py_TRASHCAN_END.
  A tp_dealloc function that has the old macros, such as:
  static void
  mytype_dealloc(mytype *p)
  {
  PyObject_GC_UnTrack(p);
  Py_TRASHCAN_SAFE_BEGIN(p);
  ...
  Py_TRASHCAN_SAFE_END
  }
  should migrate to the new macros as follows:
  static void
  mytype_dealloc(mytype *p)
  {
  PyObject_GC_UnTrack(p);
  Py_TRASHCAN_BEGIN(p, mytype_dealloc)
  ...
  Py_TRASHCAN_END
  }
  Note that Py_TRASHCAN_BEGIN has a second argument which should be the deallocation function it is in. The new macros were added in Python 3.8 and the old macros were deprecated in Python 3.11. (Contributed by Irit Katriel in gh-105111.)
• PEP 667 introduces several changes to frame-related functions:
  • The effects of mutating the dictionary returned fromPyEval_GetLocals() in an optimized scope have changed. New dict entries added this way will now only be visible to subsequent PyEval_GetLocals() calls in that frame, as PyFrame_GetLocals(), locals(), and FrameType.f_locals no longer access the same underlying cached dictionary. Changes made to entries for actual variable names and names added via the write-through proxy interfaces will be overwritten on subsequent calls to PyEval_GetLocals() in that frame. The recommended code update depends on how the function was being used, so refer to the deprecation notice on the function for details.
  • Calling PyFrame_GetLocals() in an optimized scopenow returns a write-through proxy rather than a snapshot that gets updated at ill-specified times. If a snapshot is desired, it must be created explicitly (e.g. with PyDict_Copy()), or by calling the new PyEval_GetFrameLocals() API.
  • PyFrame_FastToLocals() and PyFrame_FastToLocalsWithError()no longer have any effect. Calling these functions has been redundant since Python 3.11, when PyFrame_GetLocals() was first introduced.
  • PyFrame_LocalsToFast() no longer has any effect. Calling this function is redundant now that PyFrame_GetLocals()returns a write-through proxy for optimized scopes.
• Python 3.13 removed many private functions. Some of them can be replaced using these alternatives:
  • _PyDict_Pop(): PyDict_Pop() or PyDict_PopString();
  • _PyDict_GetItemWithError(): PyDict_GetItemRef();
  • _PyErr_WriteUnraisableMsg(): PyErr_FormatUnraisable();
  • _PyEval_SetTrace(): PyEval_SetTrace() or PyEval_SetTraceAllThreads();
  • _PyList_Extend(): PyList_Extend();
  • _PyLong_AsInt(): PyLong_AsInt();
  • _PyMem_RawStrdup(): strdup();
  • _PyMem_Strdup(): strdup();
  • _PyObject_ClearManagedDict(): PyObject_ClearManagedDict();
  • _PyObject_VisitManagedDict(): PyObject_VisitManagedDict();
  • _PyThreadState_UncheckedGet(): PyThreadState_GetUnchecked();
  • _PyTime_AsSecondsDouble(): PyTime_AsSecondsDouble();
  • _PyTime_GetMonotonicClock(): PyTime_Monotonic() or PyTime_MonotonicRaw();
  • _PyTime_GetPerfCounter(): PyTime_PerfCounter() or PyTime_PerfCounterRaw();
  • _PyTime_GetSystemClock(): PyTime_Time() or PyTime_TimeRaw();
  • _PyTime_MAX: PyTime_MAX;
  • _PyTime_MIN: PyTime_MIN;
  • _PyTime_t: PyTime_t;
  • _Py_HashPointer(): Py_HashPointer();
  • _Py_IsFinalizing(): Py_IsFinalizing().
    The pythoncapi-compat project can be used to get most of these new functions on Python 3.12 and older.

Regression Test Changes¶

• Python built with configure --with-pydebug now supports a -X presite=package.module command-line option. If used, it specifies a module that should be imported early in the lifecycle of the interpreter, before site.py is executed. (Contributed by Łukasz Langa in gh-110769.)