What's New In Python 3.13

Editors
Adam Turner and Thomas Wouters

* Anyone can add text to this document. Do not spend very much time on the wording of your changes, because your text will probably get rewritten to some degree.

* The maintainer will go through Misc/NEWS periodically and add changes; it's therefore more important to add your changes to Misc/NEWS than to this file.

* This is not a complete list of every single change; completeness is the purpose of Misc/NEWS. Some changes I consider too small or esoteric to include. If such a change is added to the text, I'll just remove it. (This is another reason you shouldn't spend too much time on writing your addition.)

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• It's helpful to add the issue number as a comment:

XXX Describe the transmogrify() function added to the socket module. (Contributed by P.Y. Developer in 12345.)

This saves the maintainer the effort of going through the VCS log when researching a change.

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 <changelog>.

Summary -- Release Highlights

Python 3.13 is a 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 (703), and a Just-In-Time compiler (744).

Error messages continue to improve, with tracebacks now highlighted in color by default. The locals builtin now has defined semantics <whatsnew313-locals-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 (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 Reference <library-index> and Language Reference <reference-index>. 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 <whatsnew313-better-interactive-interpreter> and improved error messages <whatsnew313-improved-error-messages>.
• 667: The locals builtin now has defined semantics <whatsnew313-locals-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.
• 703: CPython 3.13 has experimental support for running with the global interpreter lock disabled. See Free-threaded CPython <whatsnew313-free-threaded-cpython> for more details.
• 744: A basic JIT compiler <whatsnew313-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 <whatsnew313-better-interactive-interpreter>, as well as in tracebacks <whatsnew313-improved-error-messages> and doctest <whatsnew313-doctest> output. This can be disabled through the PYTHON_COLORS and |NO_COLOR| environment variables.

Python data model improvements:

• ~type.__static_attributes__ stores the names of attributes accessed through self.X in any function in a class body.
• ~type.__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 <interpreter shutdown>.
• 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 ~object.__replace__ method.
• The new dbm.sqlite3 module is now the default dbm backend.
• The os module has a suite of new functions <os-timerfd> for working with Linux's timer notification file descriptors.
• The random module now has a command-line interface <random-cli>.

Security improvements:

• ssl.create_default_context sets ssl.VERIFY_X509_PARTIAL_CHAIN and 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 </c-api/time> 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 functions <c-api-monitoring> for generating 669 monitoring events in the C API.

New typing features:

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

Platform support:

• 730: Apple's iOS is now an officially supported platform <whatsnew313-platform-support>, at tier 3 <11#tier-3>.
• 738: Android is now an officially supported platform <whatsnew313-platform-support>, at tier 3 <11#tier-3>.
• wasm32-wasi is now supported as a tier 2 <11#tier-2> platform.
• wasm32-emscripten is no longer an officially supported platform.

Important removals:

• PEP 594 <whatsnew313-pep594>: 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:

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 <using-on-controlling-color>.
• 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 tut-interac.

(Contributed by Pablo Galindo Salgado, Łukasz Langa, and Lysandros Nikolaou in 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 controlled <using-on-controlling-color> via the new PYTHON_COLORS environment variable as well as the canonical |NO_COLOR| and |FORCE_COLOR| environment variables. (Contributed by Pablo Galindo Salgado in 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 <module>
      import random
    File "/home/me/random.py", line 3, in <module>
      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 <module>
      import numpy as np
    File "/home/me/numpy.py", line 3, in <module>
      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 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 "<python-input-0>", line 1, in <module>
      "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 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 Windows <install-freethreaded-windows> and macOS <install-freethreaded-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 -VV <-V> and 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 <whatsnew311-pep659> 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 of locals has been left to individual Python implementations to define. Starting from Python 3.13, 667 standardises the historical behavior of CPython for most code execution scopes, but changes optimized scopes <optimized scope> (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 calling !locals 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 <frame.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 667 for more details, including related C API changes and deprecations. Porting notes are also provided below for the affected Python APIs <pep667-porting-notes-py> and C APIs <pep667-porting-notes-c>.

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

Support for mobile platforms

730: iOS is now a 11 supported platform, with the arm64-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 in 114099.)

738: Android is now a 11 supported platform, with the aarch64-linux-android and x86_64-linux-android targets at tier 3. The 32-bit targets arm-linux-androideabi and i686-linux-android are not tier 3 supported platforms, but will have best-effort support. (PEP written and implementation contributed by Malcolm Smith in 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 <bytecode> (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 withn leading whitespace.nnIt even has multiple paragraphs!n'

  (Contributed by Inada Naoki in 81283.)

• Annotation scopes <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 109118 and 118160.)

• Future statements <future> 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 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 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 <-X> command-line option. (Contributed by Yilei Yang in 111374.)

• Add support for the perf profiler <perf_profiling> working without frame pointers through the new environment variable PYTHON_PERF_JIT_SUPPORT and command-line option -X perf_jit <-X>. (Contributed by Pablo Galindo in 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 73965.)

• Classes have a new ~type.__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 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 118465.)

• The exec and eval builtins now accept the globals and locals arguments as keywords. (Contributed by Raphael Gaschignard in 105879)

• The compile builtin now accepts a new flag, ast.PyCF_OPTIMIZED_AST, which is similar to ast.PyCF_ONLY_AST except that the returned AST is optimized according to the value of the optimize argument. (Contributed by Irit Katriel in 108113).

• Add a ~property.__name__ attribute on property objects. (Contributed by Eugene Toder in 101860.)

• Add PythonFinalizationError, a new exception derived from RuntimeError and used to signal when operations are blocked during finalization <interpreter shutdown>. The following callables now raise !PythonFinalizationError, instead of RuntimeError:

  • _thread.start_new_thread
  • os.fork
  • os.forkpty
  • subprocess.Popen

  (Contributed by Victor Stinner in 114570.)

• Allow the count argument of str.replace to be a keyword. (Contributed by Hugo van Kemenade in 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 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 115961.)

New Modules

• dbm.sqlite3: An SQLite backend for dbm. (Contributed by Raymond Hettinger and Erlend E. Aasland in 100414.)

Improved Modules

argparse

• Add the deprecated parameter to the ~argparse.ArgumentParser.add_argument and !add_parser methods, to enable deprecating command-line options, positional arguments, and subcommands. (Contributed by Serhiy Storchaka in 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 80480.)
• Register array.array as a ~collections.abc.MutableSequence by implementing the ~array.array.clear method. (Contributed by Mike Zimin in 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 to Load() <ast.Load>. (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.AST unless the class opts in to the new behavior by defining the .AST._field_types mapping.

  (Contributed by Jelle Zijlstra in 105858, 117486, and 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 108113.)

asyncio

• asyncio.as_completed now returns an object that is both an asynchronous iterator and a plain iterator of awaitables <awaitable>. 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 77714.)

• asyncio.loop.create_unix_server will now automatically remove the Unix socket when the server is closed. (Contributed by Pierre Ossman in 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 115199.)

• Add Queue.shutdown <asyncio.Queue.shutdown> and ~asyncio.QueueShutDown to manage queue termination. (Contributed by Laurie Opperman and Yves Duprat in 104228.)

• Add the .Server.close_clients and .Server.abort_clients methods, which more forcefully close an asyncio server. (Contributed by Pierre Ossman in 113538.)

• Accept a tuple of separators in .StreamReader.readuntil, stopping when any one of them is encountered. (Contributed by Bruce Merry in 81322.)

• Improve the behavior of ~asyncio.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 ~asyncio.Task.cancel method. This ensures that a ~asyncio.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 (~asyncio.Task.cancelling).

  In order to handle some corner cases, ~asyncio.Task.uncancel may now reset the undocumented _must_cancel flag when the cancellation count reaches zero.

  (Inspired by an issue reported by Arthur Tacca in 116720.)

• When .TaskGroup.create_task is called on an inactive ~asyncio.TaskGroup, 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 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 ~asyncio.Task and 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 128307.)

base64

• Add ~base64.z85encode and ~base64.z85decode functions for encoding bytes as Z85 data and decoding Z85-encoded data to !bytes. (Contributed by Matan Perelman in 75299.)

compileall

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

concurrent.futures

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

configparser

• ~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 66449.)

copy

• The new ~copy.replace function and the replace protocol <object.__replace__> make creating modified copies of objects much simpler. This is especially useful when working with immutable objects. The following types support the ~copy.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 <code-objects>

  Any user-defined class can also support copy.replace by defining the ~object.__replace__ method. (Contributed by Serhiy Storchaka in 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 124520 for discussion and links to changes in some affected projects.

• ctypes.Structure objects have a new ~ctypes.Structure._align_ attribute which allows the alignment of the structure being packed to/from memory to be specified explicitly. (Contributed by Matt Sanderson in 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 100414.)
• Allow removing all items from the database through the new !clear methods of the GDBM and NDBM database objects. (Contributed by Donghee Na in 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 <dis --show-offsets> command-line option or the show_offsets argument. (Contributed by Irit Katriel in 112137.)
• ~dis.get_instructions no longer represents cache entries as separate instructions. Instead, it returns them as part of the ~dis.Instruction, in the new cache_info field. The show_caches argument to ~dis.get_instructions is deprecated and no longer has any effect. (Contributed by Irit Katriel in 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_COLOR| and |FORCE_COLOR| environment variables. See also using-on-controlling-color. (Contributed by Hugo van Kemenade in 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 108794.)

email

• Headers with embedded newlines are now quoted on output. The ~email.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 ~email.policy.Policy.verify_generated_headers. (Contributed by Bas Bloemsaat and Petr Viktorin in 121650.)
• ~email.utils.getaddresses and ~email.utils.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 102988 to improve the 2023-27043 fix.)

enum

• ~enum.EnumDict has been made public to better support subclassing ~enum.EnumType.

fractions

• ~fractions.Fraction objects now support the standard format specification mini-language <formatspec> rules for fill, alignment, sign handling, minimum width, and grouping. (Contributed by Mark Dickinson in 111320.)

glob

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

  • ~importlib.resources.is_resource
  • ~importlib.resources.open_binary
  • ~importlib.resources.open_text
  • ~importlib.resources.path
  • ~importlib.resources.read_binary
  • ~importlib.resources.read_text

  These functions are no longer deprecated and are not scheduled for removal. (Contributed by Petr Viktorin in 116608.)

• ~importlib.resources.contents remains deprecated in favor of the fully-featured ~importlib.resources.abc.Traversable API. However, there is now no plan to remove it. (Contributed by Petr Viktorin in 116608.)

io

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

ipaddress

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

itertools

• ~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 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 113626.)

math

• The new function ~math.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 73468.)

mimetypes

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

mmap

• ~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 118209.)
• ~mmap.mmap has a new ~mmap.mmap.seekable method that can be used when a seekable file-like object is required. The ~mmap.mmap.seek method now returns the new absolute position. (Contributed by Donghee Na and Sylvie Liberman in 111835.)
• The new UNIX-only trackfd parameter for ~mmap.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 78502.)

multiprocessing

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

os

• Add ~os.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 109649.)
• ~os.cpu_count and ~os.process_cpu_count can be overridden through the new environment variable PYTHON_CPU_COUNT or the new command-line option -X cpu_count <-X>. 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 109595.)
• Add a low level interface <os-timerfd> to Linux's timer file descriptors <timerfd_create(2)> via ~os.timerfd_create, ~os.timerfd_settime, ~os.timerfd_settime_ns, ~os.timerfd_gettime, ~os.timerfd_gettime_ns, ~os.TFD_NONBLOCK, ~os.TFD_CLOEXEC, ~os.TFD_TIMER_ABSTIME, and ~os.TFD_TIMER_CANCEL_ON_SET (Contributed by Masaru Tsuchiyama in 108277.)
• ~os.lchmod and the follow_symlinks argument of ~os.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 59616.)
• ~os.fchmod and support for file descriptors in ~os.chmod are both now available on Windows. (Contributed by Serhiy Storchaka in 113191.)
• On Windows, ~os.mkdir and ~os.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 2024-4030. Other values for mode continue to be ignored. (Contributed by Steve Dower in 118486.)
• ~os.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 113119.)
• ~os.posix_spawn can now use the ~os.POSIX_SPAWN_CLOSEFROM attribute in the file_actions parameter on platforms that support !posix_spawn_file_actions_addclosefrom_np. (Contributed by Jakub Kulik in 113117.)

os.path

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

pathlib

• Add ~pathlib.UnsupportedOperation, which is raised instead of NotImplementedError when a path operation isn't supported. (Contributed by Barney Gale in 89812.)
• Add a new constructor for creating ~pathlib.Path objects from 'file' URIs (file:///), .Path.from_uri. (Contributed by Barney Gale in 107465.)
• Add .PurePath.full_match for matching paths with shell-style wildcards, including the recursive wildcard "**". (Contributed by Barney Gale in 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 to .Path.glob and ~pathlib.Path.rglob. (Contributed by Barney Gale in 77609.)
• .Path.glob and ~pathlib.Path.rglob now return files and directories when given a pattern that ends with "**". Previously, only directories were returned. (Contributed by Barney Gale in 70303.)
• Add the follow_symlinks keyword-only argument to Path.is_file <pathlib.Path.is_file>, Path.is_dir <pathlib.Path.is_dir>, .Path.owner, and .Path.group. (Contributed by Barney Gale in 105793 and Kamil Turek in 107962.)

pdb

• breakpoint and ~pdb.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 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 111762.)
• zipapp is now supported as a debugging target. (Contributed by Tian Gao in 118501.)
• Add ability to move between chained exceptions during post-mortem debugging in ~pdb.pm using the new exceptions [exc_number] <exceptions> command for Pdb. (Contributed by Matthias Bussonnier in 106676.)
• Expressions and statements whose prefix is a pdb command are now correctly identified and executed. (Contributed by Tian Gao in 108464.)

queue

• Add Queue.shutdown <queue.Queue.shutdown> and ~queue.ShutDown to manage queue termination. (Contributed by Laurie Opperman and Yves Duprat in 104750.)

random

• Add a command-line interface <random-cli>. (Contributed by Hugo van Kemenade in 118131.)

re

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

shutil

• Support the dir_fd and follow_symlinks keyword arguments in ~shutil.chown. (Contributed by Berker Peksag and Tahia K in 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 117802.)

sqlite3

• A ResourceWarning is now emitted if a ~sqlite3.Connection object is not closed <sqlite3.Connection.close> explicitly. (Contributed by Erlend E. Aasland in 105539.)
• Add the filter keyword-only parameter to .Connection.iterdump for filtering database objects to dump. (Contributed by Mariusz Felisiak in 91602.)

ssl

• The ~ssl.create_default_context API now includes ~ssl.VERIFY_X509_PARTIAL_CHAIN and ~ssl.VERIFY_X509_STRICT in its default flags.

  [!NOTE] ~ssl.VERIFY_X509_STRICT may reject pre-5280 or 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 112389.)

statistics

• Add ~statistics.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 115863.)
• Add ~statistics.kde_random for sampling from an estimated probability density function created by ~statistics.kde. (Contributed by Raymond Hettinger in 115863.)

subprocess

• The subprocess module now uses the ~os.posix_spawn function in more situations.

  Notably, when close_fds is True (the default), ~os.posix_spawn will be used when the C library provides !posix_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 subprocess to never use ~os.posix_spawn. Please report your reason and platform details in the issue tracker <using-the-tracker> if you set this so that we can improve our API selection logic for everyone. (Contributed by Jakub Kulik in 113117.)

sys

• Add the ~sys._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 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 2024-4030. (Contributed by Steve Dower in 118486.)

time

• On Windows, ~time.monotonic now uses the QueryPerformanceCounter() 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 88494.)
• On Windows, ~time.time now uses the GetSystemTimePreciseAsFileTime() 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 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 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 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 43457.)
• !Text.count can now return a simple int when 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 97928.)
• Support the "vsapi" element type in the ~tkinter.ttk.Style.element_create method of tkinter.ttk.Style. (Contributed by Serhiy Storchaka in 68166.)
• Add the !after_info method for Tkinter widgets. (Contributed by Cheryl Sabella in 77020.)
• Add a new !copy_replace method to !PhotoImage to copy a region from one image to another, possibly with pixel zooming, subsampling, or both. (Contributed by Serhiy Storchaka in 118225.)
• Add from_coords parameter to the !PhotoImage methods !copy, !zoom and !subsample. Add zoom and subsample parameters to the !PhotoImage method !copy. (Contributed by Serhiy Storchaka in 118225.)
• Add the !PhotoImage methods !read 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 118271.)

traceback

• Add the ~traceback.TracebackException.exc_type_str attribute to ~traceback.TracebackException, which holds a string display of the exc_type. Deprecate the ~traceback.TracebackException.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 112332.)
• Add a new show_group keyword-only parameter to .TracebackException.format_exception_only to (recursively) format the nested exceptions of a BaseExceptionGroup instance. (Contributed by Irit Katriel in 105292.)

types

• ~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 108191.)

typing

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

unicodedata

• Update the Unicode database to version 15.1.0. (Contributed by James Gerity in 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 (~venv.EnvBuilder and ~venv.create), and opt-out via the CLI, using !--without-scm-ignore-files. (Contributed by Brett Cannon in 108125.)

warnings

• 702: The new warnings.deprecated decorator provides a way to communicate deprecations to a static type checker and 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 104003.)

xml

• Allow controlling Expat >=2.6.0 reparse deferral (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 115623.)

• Add the !close method for the iterator returned by ~xml.etree.ElementTree.iterparse for explicit cleanup. (Contributed by Serhiy Storchaka in 69893.)

zipimport

• Add support for ZIP64 format files. Everybody loves huge data, right? (Contributed by Tim Hatch in 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 include email.utils, enum, functools, importlib.metadata, and threading. (Contributed by Alex Waygood, Shantanu Jain, Adam Turner, Daniel Hollas, and others in 109653.)
• textwrap.indent is now around 30% faster than before for large input. (Contributed by Inada Naoki in 107369.)
• The subprocess module now uses the ~os.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 <whatsnew313-subprocess> section above for details. (Contributed by Jakub Kulik in 113117.)

Removed Modules And APIs

PEP 594: Remove "dead batteries" from the standard library

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 with urllib.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 calling urllib.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.EmailMessage and 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.
  • 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.quote function.
  • 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 104773 and 104780.)

2to3

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

builtins

• Remove support for chained classmethod descriptors (introduced in 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 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 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 104886.)

importlib.metadata

• Remove deprecated subscript (~object.__getitem__) access for EntryPoint <entry-points> objects. (Contributed by Jason R. Coombs in 113175.)

locale

• Remove the !locale.resetlocale function, deprecated in Python 3.11. Use locale.setlocale(locale.LC_ALL, "") instead. (Contributed by Victor Stinner in 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 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 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 126180.)

pathlib

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

re

• Remove the undocumented, deprecated, and broken !re.template function and !re.TEMPLATE / !re.T flag. (Contributed by Serhiy Storchaka and Nikita Sobolev in 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 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 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 92871.)
• Remove the keyword-argument method of creating ~typing.TypedDict types, deprecated in Python 3.11. (Contributed by Tomas Roun in 104786.)

unittest

• Remove the following unittest functions, deprecated in Python 3.11:

  • !unittest.findTestCases
  • !unittest.makeSuite
  • !unittest.getTestCaseNames

  Use ~unittest.TestLoader methods instead:

  • ~unittest.TestLoader.loadTestsFromModule
  • ~unittest.TestLoader.loadTestsFromTestCase
  • ~unittest.TestLoader.getTestCaseNames

  (Contributed by Hugo van Kemenade in 104835.)

• Remove the untested and undocumented !TestProgram.usageExit method, deprecated in Python 3.11. (Contributed by Hugo van Kemenade in 104992.)

urllib

• Remove the cafile, capath, and cadefault parameters of the urllib.request.urlopen function, deprecated in Python 3.6. Use the context parameter instead with an ~ssl.SSLContext instance. The ssl.SSLContext.load_verify_locations method can be used to load specific CA certificates, or let ssl.create_default_context select the operating system's trusted certificate authority (CA) certificates. (Contributed by Victor Stinner in 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 104804.)
• Remove the deprecated !MacOSXOSAScript._name attribute. Use the MacOSXOSAScript.name <webbrowser.controller.name> attribute instead. (Contributed by Nikita Sobolev in 105546.)

New Deprecations

• User-defined functions <user-defined-funcs>:
  • Deprecate assignment to a function's ~function.__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 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 80480.)
• ctypes:
  • Deprecate the undocumented !SetPointerType function, to be removed in Python 3.15. (Contributed by Victor Stinner in 105733.)
  • Soft-deprecate <soft deprecated> the ~ctypes.ARRAY function in favour of type * length multiplication. (Contributed by Victor Stinner in 105733.)
• decimal:
  • Deprecate the non-standard and undocumented ~decimal.Decimal format specifier 'N', which is only supported in the !decimal module's C implementation. Scheduled to be removed in Python 3.18. (Contributed by Serhiy Storchaka in 89902.)
• dis:
  • Deprecate the !HAVE_ARGUMENT separator. Check membership in ~dis.hasarg instead. (Contributed by Irit Katriel in 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 88434.)
• glob:
  • Deprecate the undocumented !glob0 and !glob1 functions. Use ~glob.glob and pass a path-like object specifying the root directory to the root_dir parameter instead. (Contributed by Barney Gale in 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 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 109096.)
• mimetypes:
  • Soft-deprecate <soft deprecated> file path arguments to ~mimetypes.guess_type, use ~mimetypes.guess_file_type instead. (Contributed by Serhiy Storchaka in 66543.)
• re:
  • Deprecate passing the optional maxsplit, count, or flags arguments as positional arguments to the module-level ~re.split, ~re.sub, and ~re.subn functions. These parameters will become keyword-only <keyword-only_parameter> in a future version of Python. (Contributed by Serhiy Storchaka in 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 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 116349.)
• pydoc:
  • Deprecate the undocumented !ispackage function. (Contributed by Zackery Spytz in 64020.)
• sqlite3:
  • Deprecate passing more than one positional argument to the ~sqlite3.connect function and the ~sqlite3.Connection constructor. The remaining parameters will become keyword-only in Python 3.15. (Contributed by Erlend E. Aasland in 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 108278.)
  • Deprecate passing the callback callable by keyword for the ~sqlite3.Connection.set_authorizer, ~sqlite3.Connection.set_progress_handler, and ~sqlite3.Connection.set_trace_callback ~sqlite3.Connection methods. The callback callables will become positional-only in Python 3.15. (Contributed by Erlend E. Aasland in 108278.)
• sys:
  • Deprecate the !_enablelegacywindowsfsencoding function, to be removed in Python 3.16. Use the PYTHONLEGACYWINDOWSFSENCODING environment variable instead. (Contributed by Inada Naoki in 73427.)
• tarfile:
  • Deprecate the undocumented and unused !TarInfo.tarfile attribute, to be removed in Python 3.16. (Contributed in 115256.)
• traceback:
  • Deprecate the .TracebackException.exc_type attribute. Use .TracebackException.exc_type_str instead. (Contributed by Irit Katriel in 112332.)
• typing:
  • Deprecate the undocumented keyword argument syntax for creating ~typing.NamedTuple 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 105566.)
  • Deprecate omitting the fields parameter when creating a ~typing.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 105566 and 105570.)
  • Deprecate the !typing.no_type_check_decorator decorator function, to be removed 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 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 <type-params> instead. (Contributed by Michael The in 107116.)
• wave:
  • Deprecate the getmark(), setmark() and getmarkers() methods of the ~wave.Wave_read and ~wave.Wave_write classes, to be removed in Python 3.15. (Contributed by Victor Stinner in 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 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 90953.)

• asyncio:

  • The child watcher classes !asyncio.MultiLoopChildWatcher, !asyncio.FastChildWatcher, !asyncio.AbstractChildWatcher and !asyncio.SafeChildWatcher are deprecated and will be removed in Python 3.14. (Contributed by Kumar Aditya in 94597.)
  • !asyncio.set_child_watcher, !asyncio.get_child_watcher, !asyncio.AbstractEventLoopPolicy.set_child_watcher and !asyncio.AbstractEventLoopPolicy.get_child_watcher are deprecated and will be removed in Python 3.14. (Contributed by Kumar Aditya in 94597.)
  • The ~asyncio.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 100160.)

• email: Deprecated the isdst parameter in email.utils.localtime. (Contributed by Alan Williams in 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 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 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 (84559). Adding a runtime warning about this was deemed too disruptive as the majority of code is not expected to care. Use the ~multiprocessing.get_context or ~multiprocessing.set_start_method APIs to explicitly specify when your code requires 'fork'. See multiprocessing-start-methods.

• pathlib: ~pathlib.PurePath.is_relative_to and ~pathlib.PurePath.relative_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 97850.)

• pty:

  • master_open(): use pty.openpty.
  • slave_open(): use pty.openpty.

• sqlite3:

  • !version and !version_info.
  • ~sqlite3.Cursor.execute and ~sqlite3.Cursor.executemany if named placeholders <sqlite3-placeholders> are used and parameters is a sequence instead of a dict.

• urllib: !urllib.parse.Quoter is deprecated: it was not intended to be a public API. (Contributed by Gregory P. Smith in 88168.)

Pending removal in Python 3.15

• The import system:
  • Setting __cached__ on a module while failing to set __spec__.cached <importlib.machinery.ModuleSpec.cached> is deprecated. In Python 3.15, __cached__ will cease to be set or take into consideration by the import system or standard library. (97879)
• ctypes:
  • The undocumented !ctypes.SetPointerType function has been deprecated since Python 3.13.
• http.server:
  • The obsolete and rarely used !CGIHTTPRequestHandler has 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.server command-line interface has been deprecated since Python 3.13.
• importlib:
  • load_module() method: use exec_module() instead.
• 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:
  • ~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 !codeobject.co_lnotab was deprecated in 626 since 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 101866.)
• typing:
  • The undocumented keyword argument syntax for creating ~typing.NamedTuple 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 ~typing.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.
• !sre_compile, !sre_constants and !sre_parse modules.
• wave:
  • The getmark(), setmark() and getmarkers() methods of the ~wave.Wave_read and ~wave.Wave_write classes have been deprecated since Python 3.13.
• zipimport:
  • !zipimport.zipimporter.load_module has been deprecated since Python 3.10. Use ~zipimport.zipimporter.exec_module instead. (125746.)

Pending removal in Python 3.16

• The import system:
  • Setting ~module.__loader__ on a module while failing to set __spec__.loader <importlib.machinery.ModuleSpec.loader> is deprecated. In Python 3.16, !__loader__ will cease to be set or taken into consideration by the import system or the standard library.
  • Setting ~module.__package__ on a module while failing to set __spec__.parent <importlib.machinery.ModuleSpec.parent> is deprecated. In Python 3.16, !__package__ will cease to be taken into consideration by the import system or standard library. (97879)
• The bundled copy of libmpdec.
• 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 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 127949.)

• builtins:
  • Bitwise inversion on boolean types, ~True or ~False has 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 115032.)
• mimetypes:
  • Valid extensions start with a '.' or are empty for mimetypes.MimeTypes.add_type. Undotted extensions are deprecated and will raise a ValueError in Python 3.16. (Contributed by Hugo van Kemenade in 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 !symtable.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 !TarInfo.tarfile attribute has been deprecated since Python 3.13.

Pending removal in Python 3.17

• datetime:
  • ~datetime.datetime.strptime calls using a format string containing %e (day of month) without a year. This has been deprecated since Python 3.15. (Contributed by Stan Ulbrych in 70647.)
• collections.abc:

  • collections.abc.ByteString is scheduled for removal in Python 3.17.

    Use isinstance(obj, collections.abc.Buffer) to test if obj implements the buffer protocol <bufferobjects> at runtime. For use in type annotations, either use ~collections.abc.Buffer or a union that explicitly specifies the types your code supports (e.g., bytes | bytearray | memoryview).

    !ByteString was originally intended to be an abstract class that would serve as a supertype of both bytes and bytearray. However, since the ABC never had any methods, knowing that an object was an instance of !ByteString never actually told you anything useful about the object. Other common buffer types such as memoryview were also never understood as subtypes of !ByteString (either at runtime or by static type checkers).

    See PEP 688 <688#current-options> for more details. (Contributed by Shantanu Jain in 91896.)

• encodings:
  • Passing non-ascii encoding names to encodings.normalize_encoding is deprecated and scheduled for removal in Python 3.17. (Contributed by Stan Ulbrych in 136702.)
• profile:
  • The !profile module is deprecated and will be removed in Python 3.17. Use profiling.tracing instead, which provides a compatible API. See 799 for details. (Contributed by Pablo Galindo and László Kiss Kollár in 138122.)
• webbrowser:
  • !webbrowser.MacOSXOSAScript is deprecated in favour of !webbrowser.MacOS. (137586)
• typing:

  • Before Python 3.14, old-style unions were implemented using the private class typing._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.

  • typing.ByteString, deprecated since Python 3.9, is scheduled for removal in Python 3.17.

    Use isinstance(obj, collections.abc.Buffer) to test if obj implements the buffer protocol <bufferobjects> at runtime. For use in type annotations, either use ~collections.abc.Buffer or a union that explicitly specifies the types your code supports (e.g., bytes | bytearray | memoryview).

    !ByteString was originally intended to be an abstract class that would serve as a supertype of both bytes and bytearray. However, since the ABC never had any methods, knowing that an object was an instance of !ByteString never actually told you anything useful about the object. Other common buffer types such as memoryview were also never understood as subtypes of !ByteString (either at runtime or by static type checkers).

    See PEP 688 <688#current-options> for more details. (Contributed by Shantanu Jain in 91896.)

• tkinter:
  • The !tkinter.Variable methods !trace_variable, !trace (an alias of !trace_variable), !trace_vdelete and !trace_vinfo, deprecated since Python 3.14, are scheduled for removal in Python 3.17. Use !trace_add, !trace_remove and !trace_info instead. (Contributed by Serhiy Storchaka in 120220.)

Pending removal in Python 3.18

• No longer accept a boolean value when a file descriptor is expected. (Contributed by Serhiy Storchaka in 82626.)

• decimal:

  • The non-standard and undocumented ~decimal.Decimal format specifier 'N', which is only supported in the !decimal module's C implementation, has been deprecated since Python 3.13. (Contributed by Serhiy Storchaka in 89902.)

• Deprecations defined by 829:

  • import lines in {name}.pth files are silently ignored.

  (Contributed by Barry Warsaw in 148641.)

Pending removal in Python 3.19

• builtins:
  • Passing a complex number as the real or imag argument in the complex constructor is now deprecated; it should only be passed as a single positional argument. (Contributed by Serhiy Storchaka in 109218.)
• ctypes:
  • Implicitly switching to the MSVC-compatible struct layout by setting ~ctypes.Structure._pack_ but not ~ctypes.Structure._layout_ on non-Windows platforms.
• hashlib:

  • In hash function constructors such as ~hashlib.new or the direct hash-named constructors such as ~hashlib.md5 and ~hashlib.sha256, their optional initial data parameter could also be passed a keyword argument named data= or string= in various !hashlib implementations.

    Support for the string keyword argument name is now deprecated and slated for removal in Python 3.19.

    Before Python 3.13, the string keyword parameter was not correctly supported depending on the backend implementation of hash functions. Prefer passing the initial data as a positional argument for maximum backwards compatibility.

• http.cookies:
  • http.cookies.Morsel.js_output is deprecated and will be removed in Python 3.19.
  • http.cookies.BaseCookie.js_output is deprecated and will be removed in Python 3.19.
• imaplib:

  • Altering IMAP4.file <imaplib.IMAP4.file> is now deprecated and slated for removal in Python 3.19. This property is now unused and changing its value does not automatically close the current file.

    Before Python 3.14, this property was used to implement the corresponding read() and readline() methods for ~imaplib.IMAP4 but this is no longer the case since then.

• tkinter:
  • tkinter.filedialog.askopenfiles has been deprecated since Python 3.16. Iterate over the names returned by ~tkinter.filedialog.askopenfilenames and open them one by one instead. (Contributed by Serhiy Storchaka in 152638.)

Pending removal in Python 3.20

• Calling the __new__() method of struct.Struct without the format argument is deprecated and will be removed in Python 3.20. Calling ~object.__init__ method on initialized ~struct.Struct objects is deprecated and will be removed in Python 3.20.

  (Contributed by Sergey B Kirpichev and Serhiy Storchaka in 143715.)

• The __version__, version and VERSION attributes have been deprecated in these standard library modules and will be removed in Python 3.20. Use sys.version_info instead.

  • argparse
  • csv
  • ctypes
  • !ctypes.macholib
  • decimal (use decimal.SPEC_VERSION instead)
  • http.server
  • imaplib
  • ipaddress
  • json
  • logging (__date__ also deprecated)
  • optparse
  • pickle
  • platform
  • re
  • socketserver
  • tabnanny
  • tarfile
  • tkinter.font
  • tkinter.ttk
  • wsgiref.simple_server
  • xml.etree.ElementTree
  • !xml.sax.expatreader
  • xml.sax.handler
  • zlib

  (Contributed by Hugo van Kemenade and Stan Ulbrych in 76007.)

• The __author__, __credits__, __copyright__ and __date__ attributes have been deprecated in these standard library modules and will be removed in Python 3.20. Attribution is preserved in the source code and the version control history.

  • bz2
  • concurrent.futures
  • inspect
  • io
  • json
  • logging
  • optparse
  • platform
  • pydoc
  • tarfile
  • tkinter.ttk
  • tokenize
  • uuid

  (Contributed by Stan Ulbrych in 159240.)

• Deprecations defined by 829:

  • Warnings are produced for import lines found in {name}.pth files.
  • {name}.pth files are no longer decoded in the locale encoding by default. They MUST be encoded in utf-8-sig.

  (Contributed by Barry Warsaw in 148641.)

• ast:

  • Creating instances of abstract AST nodes (such as ast.AST or !ast.expr) is deprecated and will raise an error in Python 3.20.

• typing:

  • It is deprecated to call isinstance and issubclass checks on protocol classes that were not explicitly decorated with !runtime_checkable but that inherit from a runtime-checkable protocol class. This will raise a TypeError in Python 3.20.

    (Contributed by Bartosz Sławecki in 132604.)

Pending removal in Python 3.21

• abc

  • Soft-deprecated since Python 3.3 abc.abstractclassmethod, abc.abstractstaticmethod, and abc.abstractproperty now raise a DeprecationWarning. These classes will be removed in Python 3.21, instead use abc.abstractmethod with classmethod, staticmethod, and property respectively.

• ast:

  • Classes slice, Index, ExtSlice, Suite, Param, AugLoad and AugStore, will be removed in Python 3.21. These types are not generated by the parser or accepted by the code generator.
  • The dims property of ast.Tuple will be removed in Python 3.21. Use the ast.Tuple.elts property instead.

• functools:

  • Using a return annotation to infer the dispatch type for functools.singledispatch or functools.singledispatchmethod is deprecated since Python 3.16 and will raise TypeError in Python 3.21. Annotate the dispatch parameter or pass the dispatch type explicitly instead. (Contributed by Bartosz Sławecki in 143465.)

• struct:

  • Soft-deprecated since Python 3.15, using 'F' and 'D' type codes are now deprecated. These codes will be removed in Python 3.21. Use instead two-letter forms 'Zf' and 'Zd'.

• tempfile:

  • tempfile._TemporaryFileWrapper will be removed in Python 3.21. Use the public tempfile.TemporaryFileWrapper instead.

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 to ~argparse.ArgumentParser.add_argument_group is now deprecated.
  • The argparse.FileType type converter is deprecated.
• builtins:
  • 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 keywords and, else, for, if, in, is and or. In a future release it will be changed to a syntax error. (87999)
  • Support for __index__() and __int__() method returning non-int type: these methods will be required to return an instance of a strict subclass of int.
  • Support for __float__() method returning a strict subclass of float: these methods will be required to return an instance of float.
  • Support for __complex__() method returning a strict subclass of complex: these methods will be required to return an instance of complex.
• calendar: calendar.January and calendar.February constants are deprecated and replaced by calendar.JANUARY and calendar.FEBRUARY. (Contributed by Prince Roshan in 103636.)
• codecs: use open instead of codecs.open. (133038)
• !codeobject.co_lnotab: use the codeobject.co_lines method instead.
• datetime:
  • ~datetime.datetime.utcnow: use datetime.datetime.now(tz=datetime.UTC).
  • ~datetime.datetime.utcfromtimestamp: use datetime.datetime.fromtimestamp(timestamp, tz=datetime.UTC).
• gettext: Plural value must be an integer.
• importlib:
  • ~importlib.util.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 ~logging.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 a multi-threaded process.
• os.path: os.path.commonprefix is deprecated, use os.path.commonpath for path prefixes. The os.path.commonprefix function is being deprecated due to having a misleading name and module. The function is not safe to use for path prefixes despite being included in a module about path manipulation, meaning it is easy to accidentally introduce path traversal vulnerabilities into Python programs by using this function.
• !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 91760.)
• shutil: ~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: ~ssl.SSLContext.set_npn_protocols and !selected_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 ~threading.Condition.notify_all.
  • !threading.Event.isSet: use ~threading.Event.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 (92332).
• The internal class typing._UnionGenericAlias is no longer used to implement typing.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 105499.)
• unittest.IsolatedAsyncioTestCase: it is deprecated to return a value that is not None from a test case.
• urllib.parse deprecated functions: ~urllib.parse.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 an ~xml.etree.ElementTree.Element is deprecated. In a future release it will always return True. Prefer explicit len(elem) or elem 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 now 1 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 111354.)

C API Changes

New Features

• Add the PyMonitoring C API <c-api-monitoring> for generating 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 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 108724.)

• Add the PyTime C API <c-api-time> 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 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 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 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 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 111262.)

• Add the PyMapping_GetOptionalItem and PyMapping_GetOptionalItemString functions as alternatives to PyObject_GetItem and PyMapping_GetItemString respectively. The new functions do not raise KeyError if 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 106307.)

• Add the PyObject_GetOptionalAttr and PyObject_GetOptionalAttrString functions as alternatives to PyObject_GetAttr and PyObject_GetAttrString respectively. The new functions do not raise AttributeError if 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 106521.)

• Add the PyErr_FormatUnraisable function as an extension to PyErr_WriteUnraisable that allows customizing the warning message. (Contributed by Serhiy Storchaka in 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 <whatsnew313-locals-semantics>:

  • PyEval_GetFrameBuiltins replaces PyEval_GetBuiltins
  • PyEval_GetFrameGlobals replaces PyEval_GetGlobals
  • PyEval_GetFrameLocals replaces PyEval_GetLocals

  (Contributed by Mark Shannon and Tian Gao in 74929.)

• Add the Py_GetConstant and Py_GetConstantBorrowed functions to get strong <strong reference> or borrowed <borrowed reference> references to constants. For example, Py_GetConstant(Py_CONSTANT_ZERO) returns a strong reference to the constant zero. (Contributed by Victor Stinner in 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 105922.)

• Add the Py_IsFinalizing function to check whether the main Python interpreter is shutting down <interpreter shutdown>. (Contributed by Victor Stinner in 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 114329.)

• Add the PyList_Extend and PyList_Clear functions, mirroring the Python list.extend and list.clear methods. (Contributed by Victor Stinner in 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 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 111140.)

• Add PyModule_Add function, which is similar to PyModule_AddObjectRef and PyModule_AddObject, but always steals a reference to the value. (Contributed by Serhiy Storchaka in 86493.)

• Add the PyObject_GenericHash function that implements the default hashing function of a Python object. (Contributed by Serhiy Storchaka in 113024.)

• Add the Py_HashPointer function to hash a raw pointer. (Contributed by Victor Stinner in 111545.)

• Add the PyObject_VisitManagedDict and PyObject_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 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 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 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 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 111696.)

• Add the PyType_GetModuleName function to get the type's module name. This is equivalent to getting the type.__module__ attribute. (Contributed by Eric Snow and Victor Stinner in 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 110289.)

• Add the PyWeakref_GetRef function as an alternative to !PyWeakref_GetObject that returns a strong reference or NULL if the referent is no longer live. (Contributed by Victor Stinner in 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 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 65210.)

• PyArg_ParseTupleAndKeywords now supports non-ASCII keyword parameter names. (Contributed by Serhiy Storchaka in 110815.)

• The !PyCode_GetFirstFree function is now unstable API and is now named PyUnstable_Code_GetFirstFree. (Contributed by Bogdan Romanyuk in 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 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 737 for more information. (Contributed by Victor Stinner in 111696.)

• You no longer have to define the PY_SSIZE_T_CLEAN macro before including Python.h when using # formats in format codes <arg-parsing-string-and-buffers>. APIs accepting the format codes always use Py_ssize_t for # formats. (Contributed by Inada Naoki in 104922.)

• If Python is built in debug mode <debug-build> or with assertions <--with-assertions>, PyTuple_SET_ITEM and PyList_SET_ITEM now check the index argument with an assertion. (Contributed by Victor Stinner in 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 85283 and 116936.)

• Python built with --with-trace-refs (tracing references) now supports the Limited API <limited-c-api>. (Contributed by Victor Stinner in 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 <using-the-tracker> to request a public C API and add cc: @vstinner to the issue to notify Victor Stinner. (Contributed by Victor Stinner in 106320.)

• Remove old buffer protocols deprecated in Python 3.0. Use bufferobjects 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 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 tuple and 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) with PyObject_Call, pass an empty tuple as positional arguments using PyTuple_New(0) <PyTuple_New>.

  • !PyEval_CallFunction: Use PyObject_CallFunction instead.

  • !PyEval_CallMethod: Use PyObject_CallMethod instead.

  • !PyCFunction_Call: Use PyObject_Call instead.

  (Contributed by Victor Stinner in 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.warnoptions 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 <init-config> instead (587), added to Python 3.8. (Contributed by Victor Stinner in 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_ReleaseThread;
  • or PyGILState_Ensure and PyGILState_Release.

  (Contributed by Victor Stinner in 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 and !PyEval_ThreadsInitialized always returns non-zero. (Contributed by Victor Stinner in 105182.)

• Remove the !_PyInterpreterState_Get alias to PyInterpreterState_Get() which was kept for backward compatibility with Python 3.8. The pythoncapi-compat project can be used to get PyInterpreterState_Get() on Python 3.8 and older. (Contributed by Victor Stinner in 106320.)

• Remove the private !_PyObject_FastCall function: use !PyObject_Vectorcall which is available since Python 3.8 (590). (Contributed by Victor Stinner in 106023.)

• Remove the cpython/pytime.h header file, which only contained private functions. (Contributed by Victor Stinner in 106316.)

• Remove the undocumented PY_TIMEOUT_MAX constant from the limited C API. (Contributed by Victor Stinner in 110014.)

• Remove the old trashcan macros Py_TRASHCAN_SAFE_BEGIN and Py_TRASHCAN_SAFE_END. Replace both with the new macros Py_TRASHCAN_BEGIN and Py_TRASHCAN_END. (Contributed by Irit Katriel in 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.home or the PYTHONHOME environment variable instead.

  (Contributed by Victor Stinner in 105145.)

• Soft deprecate <soft deprecated> the PyEval_GetBuiltins, PyEval_GetGlobals, and PyEval_GetLocals functions, which return a borrowed reference. (Soft deprecated as part of 667.)

• Deprecate the !PyImport_ImportModuleNoBlock function, which is just an alias to PyImport_ImportModule since Python 3.3. (Contributed by Victor Stinner in 105396.)

• Soft deprecate <soft deprecated> the PyModule_AddObject function. It should be replaced with PyModule_Add or PyModule_AddObjectRef. (Contributed by Serhiy Storchaka in 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_TYPE are just aliases to !wchar_t. (Contributed by Victor Stinner in 105156.)

• Deprecate the !PyWeakref_GetObject and !PyWeakref_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 get PyWeakref_GetRef on Python 3.12 and older. (Contributed by Victor Stinner in 105927.)

Pending removal in Python 3.14

• The ma_version_tag field in PyDictObject for extension modules (699; 101193).
• Creating immutable types <Py_TPFLAGS_IMMUTABLETYPE> with mutable bases (95388).

Pending removal in Python 3.15

• 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 get PyWeakref_GetRef on Python 3.12 and older.

• !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") <PyConfig_Get> (sys.path) instead.
  • !Py_GetPrefix: Use PyConfig_Get("base_prefix") <PyConfig_Get> (sys.base_prefix) instead. Use PyConfig_Get("prefix") <PyConfig_Get> (sys.prefix) if virtual environments <venv-def> need to be handled.
  • !Py_GetExecPrefix: Use PyConfig_Get("base_exec_prefix") <PyConfig_Get> (sys.base_exec_prefix) instead. Use PyConfig_Get("exec_prefix") <PyConfig_Get> (sys.exec_prefix) if virtual environments <venv-def> need to be handled.
  • !Py_GetProgramFullPath: Use PyConfig_Get("executable") <PyConfig_Get> (sys.executable) instead.
  • !Py_GetProgramName: Use PyConfig_Get("executable") <PyConfig_Get> (sys.executable) instead.
  • !Py_GetPythonHome: Use PyConfig_Get("home") <PyConfig_Get> or the PYTHONHOME environment variable instead.

  The pythoncapi-compat project can be used to get PyConfig_Get on Python 3.13 and older.

Pending removal in Python 3.16

• 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.

  The Py_InitializeFromConfig API should be used with PyConfig instead.

• Global configuration variables:

  • !Py_DebugFlag: Use PyConfig.parser_debug or PyConfig_Get("parser_debug") <PyConfig_Get> instead.
  • !Py_VerboseFlag: Use PyConfig.verbose or PyConfig_Get("verbose") <PyConfig_Get> instead.
  • !Py_QuietFlag: Use PyConfig.quiet or PyConfig_Get("quiet") <PyConfig_Get> instead.
  • !Py_InteractiveFlag: Use PyConfig.interactive or PyConfig_Get("interactive") <PyConfig_Get> instead.
  • !Py_InspectFlag: Use PyConfig.inspect or PyConfig_Get("inspect") <PyConfig_Get> instead.
  • !Py_OptimizeFlag: Use PyConfig.optimization_level or PyConfig_Get("optimization_level") <PyConfig_Get> instead.
  • !Py_NoSiteFlag: Use PyConfig.site_import or PyConfig_Get("site_import") <PyConfig_Get> instead.
  • !Py_BytesWarningFlag: Use PyConfig.bytes_warning or PyConfig_Get("bytes_warning") <PyConfig_Get> instead.
  • !Py_FrozenFlag: Use PyConfig.pathconfig_warnings or PyConfig_Get("pathconfig_warnings") <PyConfig_Get> instead.
  • !Py_IgnoreEnvironmentFlag: Use PyConfig.use_environment or PyConfig_Get("use_environment") <PyConfig_Get> instead.
  • !Py_DontWriteBytecodeFlag: Use PyConfig.write_bytecode or PyConfig_Get("write_bytecode") <PyConfig_Get> instead.
  • !Py_NoUserSiteDirectory: Use PyConfig.user_site_directory or PyConfig_Get("user_site_directory") <PyConfig_Get> instead.
  • !Py_UnbufferedStdioFlag: Use PyConfig.buffered_stdio or PyConfig_Get("buffered_stdio") <PyConfig_Get> instead.
  • !Py_HashRandomizationFlag: Use PyConfig.use_hash_seed and PyConfig.hash_seed or PyConfig_Get("hash_seed") <PyConfig_Get> instead.
  • !Py_IsolatedFlag: Use PyConfig.isolated or PyConfig_Get("isolated") <PyConfig_Get> instead.
  • !Py_LegacyWindowsFSEncodingFlag: Use PyPreConfig.legacy_windows_fs_encoding or PyConfig_Get("legacy_windows_fs_encoding") <PyConfig_Get> instead.
  • !Py_LegacyWindowsStdioFlag: Use PyConfig.legacy_windows_stdio or PyConfig_Get("legacy_windows_stdio") <PyConfig_Get> instead.
  • !Py_FileSystemDefaultEncoding, !Py_HasFileSystemDefaultEncoding: Use PyConfig.filesystem_encoding or PyConfig_Get("filesystem_encoding") <PyConfig_Get> instead.
  • !Py_FileSystemDefaultEncodeErrors: Use PyConfig.filesystem_errors or PyConfig_Get("filesystem_errors") <PyConfig_Get> instead.
  • !Py_UTF8Mode: Use PyPreConfig.utf8_mode or PyConfig_Get("utf8_mode") <PyConfig_Get> instead. (see Py_PreInitialize)

  The Py_InitializeFromConfig API should be used with PyConfig to set these options. Or PyConfig_Get can be used to get these options at runtime.

• Py_UNICODE which was deprecated by 393.

Pending removal in Python 3.18

• The following private functions are deprecated and planned for removal in Python 3.18:

  • !_PyBytes_Join: use PyBytes_Join.
  • !_PyDict_GetItemStringWithError: use PyDict_GetItemStringRef.
  • !_PyDict_Pop(): use 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) with writer = PyUnicodeWriter_Create(0) <PyUnicodeWriter_Create>.
  • !_PyUnicodeWriter_Finish: replace _PyUnicodeWriter_Finish(&writer) with PyUnicodeWriter_Finish(writer) <PyUnicodeWriter_Finish>.
  • !_PyUnicodeWriter_Dealloc: replace _PyUnicodeWriter_Dealloc(&writer) with PyUnicodeWriter_Discard(writer) <PyUnicodeWriter_Discard>.
  • !_PyUnicodeWriter_WriteChar: replace _PyUnicodeWriter_WriteChar(&writer, ch) with PyUnicodeWriter_WriteChar(writer, ch) <PyUnicodeWriter_WriteChar>.
  • !_PyUnicodeWriter_WriteStr: replace _PyUnicodeWriter_WriteStr(&writer, str) with PyUnicodeWriter_WriteStr(writer, str) <PyUnicodeWriter_WriteStr>.
  • !_PyUnicodeWriter_WriteSubstring: replace _PyUnicodeWriter_WriteSubstring(&writer, str, start, end) with PyUnicodeWriter_WriteSubstring(writer, str, start, end) <PyUnicodeWriter_WriteSubstring>.
  • !_PyUnicodeWriter_WriteASCIIString: replace _PyUnicodeWriter_WriteASCIIString(&writer, str, size) with PyUnicodeWriter_WriteASCII(writer, str, size) <PyUnicodeWriter_WriteASCII>.
  • !_PyUnicodeWriter_WriteLatin1String: replace _PyUnicodeWriter_WriteLatin1String(&writer, str, size) by decoding the string with PyUnicode_DecodeLatin1, writing the result with PyUnicodeWriter_WriteStr, and releasing the result with Py_DECREF.
  • !_PyUnicodeWriter_Prepare: (no replacement).
  • !_PyUnicodeWriter_PrepareKind: (no replacement).
  • !_Py_HashPointer: use Py_HashPointer.
  • !_Py_fopen_obj: use Py_fopen.
  • PyGen_New: (no replacement).
  • PyGen_NewWithQualName: (no replacement).
  • PyCoro_New: (no replacement).
  • PyAsyncGen_New: (no replacement).

  The pythoncapi-compat project can be used to get these new public functions on Python 3.13 and older. (Contributed by Victor Stinner in 128863.)

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.
• 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 11 tier 3 platforms. (PEP 730 <whatsnew313-platform-support> written and implementation contributed by Russell Keith-Magee in 114099.)
• aarch64-linux-android and x86_64-linux-android are both now 11 tier 3 platforms. (PEP 738 <whatsnew313-platform-support> written and implementation contributed by Malcolm Smith in 116622.)
• wasm32-wasi is now a 11 tier 2 platform. (Contributed by Brett Cannon in 115192.)
• wasm32-emscripten is no longer a 11 supported platform. (Contributed by Brett Cannon in 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 89886 and by Victor Stinner in 112090.)
• SQLite 3.15.2 or newer is required to build the sqlite3 extension module. (Contributed by Erlend Aasland in 105875.)
• CPython now bundles the mimalloc library by default. It is licensed under the MIT license; see mimalloc license <mimalloc-license>. The bundled mimalloc has custom changes, see 113141 for details. (Contributed by Dino Viehland in 109914.)
• The configure option !--with-system-libmpdec now defaults to yes. The bundled copy of libmpdec will be removed in Python 3.16.
• Python built with configure --with-trace-refs (tracing references) is now ABI compatible with the Python release build and debug build <debug-build>. (Contributed by Victor Stinner in 108634.)
• On POSIX systems, the pkg-config (.pc) filenames now include the ABI flags. For example, the free-threaded build generates python-3.13t.pc and 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 _uuid C extensions are now built with the limited C API <limited-c-api>. (Contributed by Victor Stinner in 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

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 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 and !gmtime functions, <sys/select.h> provides the !select function, and <sys/time.h> provides the !futimes, !gettimeofday and !setitimer functions. (Contributed by Victor Stinner in 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 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 85283.)

• The old trashcan macros Py_TRASHCAN_SAFE_BEGIN and Py_TRASHCAN_SAFE_END were removed. They should be replaced by the new macros Py_TRASHCAN_BEGIN and 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(p)
  }
  

  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 105111.)

Regression Test Changes

• Python built with configure --with-pydebug now supports a -X presite=package.module <-X> 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 110769.)