What's New In Python 3.13
*************************

Editors:
   Adam Turner and Thomas Wouters

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

See also: **PEP 719** -- Python 3.13 Release Schedule


Summary -- Release Highlights
=============================

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

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

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

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

======================================================================

Interpreter improvements:

* A greatly improved interactive interpreter and improved error
  messages.

* **PEP 667**: The "locals()" builtin now has defined semantics when
  mutating the returned mapping. Python debuggers and similar tools
  may now more reliably update local variables in optimized scopes
  even during concurrent code execution.

* **PEP 703**: CPython 3.13 has experimental support for running with
  the *global interpreter lock* disabled. See Free-threaded CPython
  for more details.

* **PEP 744**: A basic JIT compiler was added. It is currently
  disabled by default (though we may turn it on later). Performance
  improvements are modest -- we expect to improve this over the next
  few releases.

* Color support in the new interactive interpreter, as well as in
  tracebacks and doctest output. This can be disabled through the
  "PYTHON_COLORS" and "NO_COLOR" environment variables.

Python data model improvements:

* "__static_attributes__" stores the names of attributes accessed
  through "self.X" in any function in a class body.

* "__firstlineno__" records the first line number of a class
  definition.

Significant improvements in the standard library:

* Add a new "PythonFinalizationError" exception, raised when an
  operation is blocked during *finalization*.

* The "argparse" module now supports deprecating command-line options,
  positional arguments, and subcommands.

* The new functions "base64.z85encode()" and "base64.z85decode()"
  support encoding and decoding Z85 data.

* The "copy" module now has a "copy.replace()" function, with support
  for many builtin types and any class defining the "__replace__()"
  method.

* The new "dbm.sqlite3" module is now the default "dbm" backend.

* The "os" module has a suite of new functions for working with
  Linux's timer notification file descriptors.

* The "random" module now has a command-line interface.

Security improvements:

* "ssl.create_default_context()" sets "ssl.VERIFY_X509_PARTIAL_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 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 for generating **PEP 669**
  monitoring events in the C API.

New typing features:

* **PEP 696**: Type parameters ("typing.TypeVar", "typing.ParamSpec",
  and "typing.TypeVarTuple") now support defaults.

* **PEP 702**: The new "warnings.deprecated()" decorator adds support
  for marking deprecations in the type system and at runtime.

* **PEP 705**: "typing.ReadOnly" can be used to mark an item of a
  "typing.TypedDict" as read-only for type checkers.

* **PEP 742**: "typing.TypeIs" provides more intuitive type narrowing
  behavior, as an alternative to "typing.TypeGuard".

Platform support:

* **PEP 730**: Apple's iOS is now an officially supported platform, at
  **tier 3**.

* **PEP 738**: Android is now an officially supported platform, at
  **tier 3**.

* "wasm32-wasi" is now supported as a **tier 2** platform.

* "wasm32-emscripten" is no longer an officially supported platform.

Important removals:

* PEP 594: The remaining 19 "dead batteries" (legacy stdlib modules)
  have been removed from the standard library: "aifc", "audioop",
  "cgi", "cgitb", "chunk", "crypt", "imghdr", "mailcap", "msilib",
  "nis", "nntplib", "ossaudiodev", "pipes", "sndhdr", "spwd", "sunau",
  "telnetlib", "uu" and "xdrlib".

* Remove the **2to3** tool and "lib2to3" module (deprecated in Python
  3.11).

* Remove the "tkinter.tix" module (deprecated in Python 3.6).

* Remove the "locale.resetlocale()" function.

* Remove the "typing.io" and "typing.re" namespaces.

* Remove chained "classmethod" descriptors.

Release schedule changes:

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

* Python 3.9--3.12 have one and a half years of full support, followed
  by three and a half years of security fixes.

* Python 3.13 and later have two years of full support, followed by
  three years of security fixes.


New Features
============


A better interactive interpreter
--------------------------------

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

* Multiline editing with history preservation.

* Direct support for REPL-specific commands like "help", "exit", and
  "quit", without the need to call them as functions.

* Prompts and tracebacks with color enabled by default.

* Interactive help browsing using "F1" with a separate command
  history.

* History browsing using "F2" that skips output as well as the *>>>*
  and *...* prompts.

* "Paste mode" with "F3" that makes pasting larger blocks of code
  easier (press "F3" again to return to the regular prompt).

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

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


Improved error messages
-----------------------

* The interpreter now uses color by default when displaying tracebacks
  in the terminal. This feature can be controlled 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 gh-112730.)

* A common mistake is to write a script with the same name as a
  standard library module. When this results in errors, we now display
  a more helpful error message:

     $ python random.py
     Traceback (most recent call last):
       File "/home/me/random.py", line 1, in <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 gh-95754.)

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

     >>> "Better error messages!".split(max_split=1)
     Traceback (most recent call last):
       File "<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
  gh-107944.)


Free-threaded CPython
---------------------

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

See also:

  **PEP 703** "Making the Global Interpreter Lock Optional in CPython"
  contains rationale and information surrounding this work.

  Porting Extension Modules to Support Free-Threading: A community-
  maintained porting guide for extension authors.


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

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

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

* "no": Disable the entire Tier 2 and JIT pipeline.

* "yes": Enable the JIT. To disable the JIT at runtime, pass the
  environment variable "PYTHON_JIT=0".

* "yes-off": Build the JIT but disable it by default. To enable the
  JIT at runtime, pass the environment variable "PYTHON_JIT=1".

* "interpreter": Enable the Tier 2 interpreter but disable the JIT.
  The interpreter can be disabled by running with "PYTHON_JIT=0".

The internal architecture is roughly as follows:

* We start with specialized *Tier 1 bytecode*. See What's new in 3.11
  for details.

* When the Tier 1 bytecode gets hot enough, it gets translated to a
  new purely internal intermediate representation (IR), called the
  *Tier 2 IR*, and sometimes referred to as micro-ops ("uops").

* The Tier 2 IR uses the same stack-based virtual machine as Tier 1,
  but the instruction format is better suited to translation to
  machine code.

* We have several optimization passes for Tier 2 IR, which are applied
  before it is interpreted or translated to machine code.

* There is a Tier 2 interpreter, but it is mostly intended for
  debugging the earlier stages of the optimization pipeline. The Tier
  2 interpreter can be enabled by configuring Python with "--enable-
  experimental-jit=interpreter".

* When the JIT is enabled, the optimized Tier 2 IR is translated to
  machine code, which is then executed.

* The machine code translation process uses a technique called *copy-
  and-patch*. It has no runtime dependencies, but there is a new
  build-time dependency on LLVM.

See also: **PEP 744**

(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, **PEP 667** standardises the
historical behavior of CPython for most code execution scopes, but
changes *optimized scopes* (functions, generators, coroutines,
comprehensions, and generator expressions) to explicitly return
independent snapshots of the currently assigned local variables,
including locally referenced nonlocal variables captured in closures.

This change to the semantics of "locals()" in optimized scopes also
affects the default behavior of code execution functions that
implicitly target "locals()" if no explicit namespace is provided
(such as "exec()" and "eval()"). In previous versions, whether or not
changes could be accessed by 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" now
returns a write-through proxy to the frame's local and locally
referenced nonlocal variables in these scopes, rather than returning
an inconsistently updated shared "dict" instance with undefined
runtime semantics.

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

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


Support for mobile platforms
----------------------------

**PEP 730**: iOS is now a **PEP 11** supported platform, with 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 gh-114099.)

**PEP 738**: Android is now a **PEP 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
gh-116622.)

See also: **PEP 730**, **PEP 738**


Other Language Changes
======================

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

     >>> def spam():
     ...     """
     ...         This is a docstring with
     ...           leading whitespace.
     ...
     ...         It even has multiple paragraphs!
     ...     """
     ...
     >>> spam.__doc__
     '\nThis is a docstring with\n  leading whitespace.\n\nIt even has multiple paragraphs!\n'

  (Contributed by Inada Naoki in gh-81283.)

* Annotation scopes within class scopes can now contain lambdas and
  comprehensions. Comprehensions that are located within class scopes
  are not inlined into their parent scope.

     class C[T]:
         type Alias = lambda: T

  (Contributed by Jelle Zijlstra in gh-109118 and gh-118160.)

* Future statements are no longer triggered by relative imports of the
  "__future__" module, meaning that statements of the form "from
  .__future__ import ..." are now simply standard relative imports,
  with no special features activated. (Contributed by Jeremiah Gabriel
  Pascual in gh-118216.)

* "global" declarations are now permitted in "except" blocks when that
  global is used in the "else" block. Previously this raised an
  erroneous "SyntaxError". (Contributed by Irit Katriel in gh-111123.)

* Add "PYTHON_FROZEN_MODULES", a new environment variable that
  determines whether frozen modules are ignored by the import
  machinery, equivalent to the "-X frozen_modules" command-line
  option. (Contributed by Yilei Yang in gh-111374.)

* Add support for the perf profiler working without frame pointers
  through the new environment variable "PYTHON_PERF_JIT_SUPPORT" and
  command-line option "-X perf_jit". (Contributed by Pablo Galindo in
  gh-118518.)

* The location of a ".python_history" file can be changed via the new
  "PYTHON_HISTORY" environment variable. (Contributed by Levi Sabah,
  Zackery Spytz and Hugo van Kemenade in gh-73965.)

* Classes have a new "__static_attributes__" attribute. This is
  populated by the compiler with a tuple of the class's attribute
  names which are assigned through "self.<name>" from any function in
  its body. (Contributed by Irit Katriel in gh-115775.)

* The compiler now creates a "__firstlineno__" attribute on classes
  with the line number of the first line of the class definition.
  (Contributed by Serhiy Storchaka in gh-118465.)

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

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

* Add a "__name__" attribute on "property" objects. (Contributed by
  Eugene Toder in gh-101860.)

* Add "PythonFinalizationError", a new exception derived from
  "RuntimeError" and used to signal when operations are blocked during
  *finalization*. The following callables now raise
  "PythonFinalizationError", instead of "RuntimeError":

  * "_thread.start_new_thread()"

  * "os.fork()"

  * "os.forkpty()"

  * "subprocess.Popen"

  (Contributed by Victor Stinner in gh-114570.)

* Allow the *count* argument of "str.replace()" to be a keyword.
  (Contributed by Hugo van Kemenade in gh-106487.)

* Many functions now emit a warning if a boolean value is passed as a
  file descriptor argument. This can help catch some errors earlier.
  (Contributed by Serhiy Storchaka in gh-82626.)

* Added "name" and "mode" attributes for compressed and archived file-
  like objects in the "bz2", "lzma", "tarfile", and "zipfile" modules.
  (Contributed by Serhiy Storchaka in gh-115961.)


New Modules
===========

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


Improved Modules
================


argparse
--------

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


array
-----

* Add the "'w'" type code ("Py_UCS4") for Unicode characters. It
  should be used instead of the deprecated "'u'" type code.
  (Contributed by Inada Naoki in gh-80480.)

* Register "array.array" as a "MutableSequence" by implementing the
  "clear()" method. (Contributed by Mike Zimin in gh-114894.)


ast
---

* The constructors of node types in the "ast" module are now stricter
  in the arguments they accept, with more intuitive behavior when
  arguments are omitted.

  If an optional field on an AST node is not included as an argument
  when constructing an instance, the field will now be set to "None".
  Similarly, if a list field is omitted, that field will now be set to
  an empty list, and if an "expr_context" field is omitted, it
  defaults to "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 gh-105858, gh-117486, and
  gh-118851.)

* "ast.parse()" now accepts an optional argument *optimize* which is
  passed on to "compile()". This makes it possible to obtain an
  optimized AST. (Contributed by Irit Katriel in gh-108113.)


asyncio
-------

* "asyncio.as_completed()" now returns an object that is both an
  *asynchronous iterator* and a plain *iterator* of *awaitables*. The
  awaitables yielded by asynchronous iteration include original task
  or future objects that were passed in, making it easier to associate
  results with the tasks being completed. (Contributed by Justin
  Arthur in gh-77714.)

* "asyncio.loop.create_unix_server()" will now automatically remove
  the Unix socket when the server is closed. (Contributed by Pierre
  Ossman in gh-111246.)

* "DatagramTransport.sendto()" will now send zero-length datagrams if
  called with an empty bytes object. The transport flow control also
  now accounts for the datagram header when calculating the buffer
  size. (Contributed by Jamie Phan in gh-115199.)

* Add "Queue.shutdown" and "QueueShutDown" to manage queue
  termination. (Contributed by Laurie Opperman and Yves Duprat in
  gh-104228.)

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

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

* Improve the behavior of "TaskGroup" when an external cancellation
  collides with an internal cancellation. For example, when two task
  groups are nested and both experience an exception in a child task
  simultaneously, it was possible that the outer task group would
  hang, because its internal cancellation was swallowed by the inner
  task group.

  In the case where a task group is cancelled externally and also must
  raise an "ExceptionGroup", it will now call the parent task's
  "cancel()" method. This ensures that a "CancelledError" will be
  raised at the next "await", so the cancellation is not lost.

  An added benefit of these changes is that task groups now preserve
  the cancellation count ("cancelling()").

  In order to handle some corner cases, "uncancel()" may now reset the
  undocumented "_must_cancel" flag when the cancellation count reaches
  zero.

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

* When "TaskGroup.create_task()" is called on an inactive "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 gh-115957.)

* The function and methods named "create_task" have received a new
  "**kwargs" argument that is passed through to the task constructor.
  This change was accidentally added in 3.13.3, and broke the API
  contract for custom task factories. Several third-party task
  factories implemented workarounds for this. In 3.13.4 and later
  releases the old factory contract is honored once again (until
  3.14). To keep the workarounds working, the extra "**kwargs"
  argument still allows passing additional keyword arguments to "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 gh-128307.)


base64
------

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


compileall
----------

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


concurrent.futures
------------------

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


configparser
------------

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


copy
----

* The new "replace()" function and the "replace protocol" make
  creating modified copies of objects much simpler. This is especially
  useful when working with immutable objects. The following types
  support the "replace()" function and implement the replace protocol:

  * "collections.namedtuple()"

  * "dataclasses.dataclass"

  * "datetime.datetime", "datetime.date", "datetime.time"

  * "inspect.Signature", "inspect.Parameter"

  * "types.SimpleNamespace"

  * code objects

  Any user-defined class can also support "copy.replace()" by defining
  the "__replace__()" method. (Contributed by Serhiy Storchaka in
  gh-108751.)


ctypes
------

* As a consequence of necessary internal refactoring, initialization
  of internal metaclasses now happens in "__init__" rather than in
  "__new__". This affects projects that subclass these internal
  metaclasses to provide custom initialization. Generally:

  * Custom logic that was done in "__new__" after calling
    "super().__new__" should be moved to "__init__".

  * To create a class, call the metaclass, not only the metaclass's
    "__new__" method.

  See gh-124520 for discussion and links to changes in some affected
  projects.

* "ctypes.Structure" objects have a new "_align_" attribute which
  allows the alignment of the structure being packed to/from memory to
  be specified explicitly. (Contributed by Matt Sanderson in
  gh-112433)


dbm
---

* Add "dbm.sqlite3", a new module which implements an SQLite backend,
  and make it the default "dbm" backend. (Contributed by Raymond
  Hettinger and Erlend E. Aasland in gh-100414.)

* Allow removing all items from the database through the new "clear()"
  methods of the GDBM and NDBM database objects. (Contributed by
  Donghee Na in gh-107122.)


dis
---

* Change the output of "dis" module functions to show logical labels
  for jump targets and exception handlers, rather than offsets. The
  offsets can be added with the new "-O" command-line option or the
  *show_offsets* argument. (Contributed by Irit Katriel in gh-112137.)

* "get_instructions()" no longer represents cache entries as separate
  instructions. Instead, it returns them as part of the "Instruction",
  in the new *cache_info* field. The *show_caches* argument to
  "get_instructions()" is deprecated and no longer has any effect.
  (Contributed by Irit Katriel in gh-112962.)


doctest
-------

* "doctest" output is now colored by default. This can be controlled
  via the new "PYTHON_COLORS" environment variable as well as the
  canonical "NO_COLOR" and "FORCE_COLOR" environment variables. See
  also Controlling color. (Contributed by Hugo van Kemenade in
  gh-117225.)

* The "DocTestRunner.run()" method now counts the number of skipped
  tests. Add the "DocTestRunner.skips" and "TestResults.skipped"
  attributes. (Contributed by Victor Stinner in gh-108794.)


email
-----

* Headers with embedded newlines are now quoted on output. The
  "generator" will now refuse to serialize (write) headers that are
  improperly folded or delimited, such that they would be parsed as
  multiple headers or joined with adjacent data. If you need to turn
  this safety feature off, set "verify_generated_headers".
  (Contributed by Bas Bloemsaat and Petr Viktorin in gh-121650.)

* "getaddresses()" and "parseaddr()" now return "('', '')" pairs in
  more situations where invalid email addresses are encountered
  instead of potentially inaccurate values. The two functions have a
  new optional *strict* parameter (default "True"). To get the old
  behavior (accepting malformed input), use "strict=False".
  "getattr(email.utils, 'supports_strict_parsing', False)" can be used
  to check if the *strict* parameter is available. (Contributed by
  Thomas Dwyer and Victor Stinner for gh-102988 to improve the **CVE
  2023-27043** fix.)


enum
----

* "EnumDict" has been made public to better support subclassing
  "EnumType".


fractions
---------

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


glob
----

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


importlib
---------

* The following functions in "importlib.resources" now allow accessing
  a directory (or tree) of resources, using multiple positional
  arguments (the *encoding* and *errors* arguments in the text-reading
  functions are now keyword-only):

  * "is_resource()"

  * "open_binary()"

  * "open_text()"

  * "path()"

  * "read_binary()"

  * "read_text()"

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

* "contents()" remains deprecated in favor of the fully-featured
  "Traversable" API. However, there is now no plan to remove it.
  (Contributed by Petr Viktorin in gh-116608.)


io
--

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


ipaddress
---------

* Add the "IPv4Address.ipv6_mapped" property, which returns the
  IPv4-mapped IPv6 address. (Contributed by Charles Machalow in
  gh-109466.)

* Fix "is_global" and "is_private" behavior in "IPv4Address",
  "IPv6Address", "IPv4Network", and "IPv6Network". (Contributed by
  Jakub Stasiak in gh-113171.)


itertools
---------

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


marshal
-------

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


math
----

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


mimetypes
---------

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


mmap
----

* "mmap" is now protected from crashing on Windows when the mapped
  memory is inaccessible due to file system errors or access
  violations. (Contributed by Jannis Weigend in gh-118209.)

* "mmap" has a new "seekable()" method that can be used when a
  seekable file-like object is required. The "seek()" method now
  returns the new absolute position. (Contributed by Donghee Na and
  Sylvie Liberman in gh-111835.)

* The new UNIX-only *trackfd* parameter for "mmap" controls file
  descriptor duplication; if false, the file descriptor specified by
  *fileno* will not be duplicated. (Contributed by Zackery Spytz and
  Petr Viktorin in gh-78502.)


multiprocessing
---------------

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


os
--

* Add "process_cpu_count()" function to get the number of logical CPU
  cores usable by the calling thread of the current process.
  (Contributed by Victor Stinner in gh-109649.)

* "cpu_count()" and "process_cpu_count()" can be overridden through
  the new environment variable "PYTHON_CPU_COUNT" or the new command-
  line option "-X cpu_count". This option is useful for users who need
  to limit CPU resources of a container system without having to
  modify application code or the container itself. (Contributed by
  Donghee Na in gh-109595.)

* Add a low level interface to Linux's *timer file descriptors* via
  "timerfd_create()", "timerfd_settime()", "timerfd_settime_ns()",
  "timerfd_gettime()", "timerfd_gettime_ns()", "TFD_NONBLOCK",
  "TFD_CLOEXEC", "TFD_TIMER_ABSTIME", and "TFD_TIMER_CANCEL_ON_SET"
  (Contributed by Masaru Tsuchiyama in gh-108277.)

* "lchmod()" and the *follow_symlinks* argument of "chmod()" are both
  now available on Windows. Note that the default value of
  *follow_symlinks* in "lchmod()" is "False" on Windows. (Contributed
  by Serhiy Storchaka in gh-59616.)

* "fchmod()" and support for file descriptors in "chmod()" are both
  now available on Windows. (Contributed by Serhiy Storchaka in
  gh-113191.)

* On Windows, "mkdir()" and "makedirs()" now support passing a *mode*
  value of "0o700" to apply access control to the new directory. This
  implicitly affects "tempfile.mkdtemp()" and is a mitigation for
  **CVE 2024-4030**. Other values for *mode* continue to be ignored.
  (Contributed by Steve Dower in gh-118486.)

* "posix_spawn()" now accepts "None" for the *env* argument, which
  makes the newly spawned process use the current process environment.
  (Contributed by Jakub Kulik in gh-113119.)

* "posix_spawn()" can now use the "POSIX_SPAWN_CLOSEFROM" attribute in
  the *file_actions* parameter on platforms that support
  "posix_spawn_file_actions_addclosefrom_np()". (Contributed by Jakub
  Kulik in gh-113117.)


os.path
-------

* Add "isreserved()" to check if a path is reserved on the current
  system. This function is only available on Windows. (Contributed by
  Barney Gale in gh-88569.)

* On Windows, "isabs()" no longer considers paths starting with
  exactly one slash ("\" or "/") to be absolute. (Contributed by
  Barney Gale and Jon Foster in gh-44626.)

* "realpath()" now resolves MS-DOS style file names even if the file
  is not accessible. (Contributed by Moonsik Park in gh-82367.)


pathlib
-------

* Add "UnsupportedOperation", which is raised instead of
  "NotImplementedError" when a path operation isn't supported.
  (Contributed by Barney Gale in gh-89812.)

* Add a new constructor for creating "Path" objects from 'file' URIs
  ("file:///"), "Path.from_uri()". (Contributed by Barney Gale in
  gh-107465.)

* Add "PurePath.full_match()" for matching paths with shell-style
  wildcards, including the recursive wildcard ""**"". (Contributed by
  Barney Gale in gh-73435.)

* Add the "PurePath.parser" class attribute to store the
  implementation of "os.path" used for low-level path parsing and
  joining. This will be either "posixpath" or "ntpath".

* Add *recurse_symlinks* keyword-only argument to "Path.glob()" and
  "rglob()". (Contributed by Barney Gale in gh-77609.)

* "Path.glob()" and "rglob()" now return files and directories when
  given a pattern that ends with ""**"". Previously, only directories
  were returned. (Contributed by Barney Gale in gh-70303.)

* Add the *follow_symlinks* keyword-only argument to "Path.is_file",
  "Path.is_dir", "Path.owner()", and "Path.group()". (Contributed by
  Barney Gale in gh-105793 and Kamil Turek in gh-107962.)


pdb
---

* "breakpoint()" and "set_trace()" now enter the debugger immediately
  rather than on the next line of code to be executed. This change
  prevents the debugger from breaking outside of the context when
  "breakpoint()" is positioned at the end of the context. (Contributed
  by Tian Gao in gh-118579.)

* "sys.path[0]" is no longer replaced by the directory of the script
  being debugged when "sys.flags.safe_path" is set. (Contributed by
  Tian Gao and Christian Walther in gh-111762.)

* "zipapp" is now supported as a debugging target. (Contributed by
  Tian Gao in gh-118501.)

* Add ability to move between chained exceptions during post-mortem
  debugging in "pm()" using the new "exceptions [exc_number]" command
  for Pdb. (Contributed by Matthias Bussonnier in gh-106676.)

* Expressions and statements whose prefix is a pdb command are now
  correctly identified and executed. (Contributed by Tian Gao in
  gh-108464.)


queue
-----

* Add "Queue.shutdown" and "ShutDown" to manage queue termination.
  (Contributed by Laurie Opperman and Yves Duprat in gh-104750.)


random
------

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


re
--

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


shutil
------

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


site
----

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


sqlite3
-------

* A "ResourceWarning" is now emitted if a "Connection" object is not
  "closed" explicitly. (Contributed by Erlend E. Aasland in
  gh-105539.)

* Add the *filter* keyword-only parameter to "Connection.iterdump()"
  for filtering database objects to dump. (Contributed by Mariusz
  Felisiak in gh-91602.)


ssl
---

* The "create_default_context()" API now includes
  "VERIFY_X509_PARTIAL_CHAIN" and "VERIFY_X509_STRICT" in its default
  flags.

  Note:

    "VERIFY_X509_STRICT" may reject pre-**RFC 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 gh-112389.)


statistics
----------

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

* Add "kde_random()" for sampling from an estimated probability
  density function created by "kde()". (Contributed by Raymond
  Hettinger in gh-115863.)


subprocess
----------

* The "subprocess" module now uses the "posix_spawn()" function in
  more situations.

  Notably, when *close_fds* is "True" (the default), "posix_spawn()"
  will be used when the C library 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
  "posix_spawn()". Please report your reason and platform details in
  the issue tracker if you set this so that we can improve our API
  selection logic for everyone. (Contributed by Jakub Kulik in
  gh-113117.)


sys
---

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


tempfile
--------

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


time
----

* On Windows, "monotonic()" now uses 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 gh-88494.)

* On Windows, "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 gh-63207.)


tkinter
-------

* Add "tkinter" widget methods: "tk_busy_hold()",
  "tk_busy_configure()", "tk_busy_cget()", "tk_busy_forget()",
  "tk_busy_current()", and "tk_busy_status()". (Contributed by Miguel,
  klappnase and Serhiy Storchaka in gh-72684.)

* The "tkinter" widget method "wm_attributes()" now accepts the
  attribute name without the minus prefix to get window attributes,
  for example "w.wm_attributes('alpha')" and allows specifying
  attributes and values to set as keyword arguments, for example
  "w.wm_attributes(alpha=0.5)". (Contributed by Serhiy Storchaka in
  gh-43457.)

* "wm_attributes()" can now return attributes as a "dict", by using
  the new optional keyword-only parameter *return_python_dict*.
  (Contributed by Serhiy Storchaka in gh-43457.)

* "Text.count()" can now return a simple "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 gh-97928.)

* Support the "vsapi" element type in the "element_create()" method of
  "tkinter.ttk.Style". (Contributed by Serhiy Storchaka in gh-68166.)

* Add the "after_info()" method for Tkinter widgets. (Contributed by
  Cheryl Sabella in gh-77020.)

* Add a new "copy_replace()" method to "PhotoImage" to copy a region
  from one image to another, possibly with pixel zooming, subsampling,
  or both. (Contributed by Serhiy Storchaka in gh-118225.)

* Add *from_coords* parameter to the "PhotoImage" methods "copy()",
  "zoom()" and "subsample()". Add *zoom* and *subsample* parameters to
  the "PhotoImage" method "copy()". (Contributed by Serhiy Storchaka
  in gh-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 gh-118271.)


traceback
---------

* Add the "exc_type_str" attribute to "TracebackException", which
  holds a string display of the *exc_type*. Deprecate the "exc_type"
  attribute, which holds the type object itself. Add parameter
  *save_exc_type* (default "True") to indicate whether "exc_type"
  should be saved. (Contributed by Irit Katriel in gh-112332.)

* Add a new *show_group* keyword-only parameter to
  "TracebackException.format_exception_only()" to (recursively) format
  the nested exceptions of a "BaseExceptionGroup" instance.
  (Contributed by Irit Katriel in gh-105292.)


types
-----

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


typing
------

* **PEP 705**: Add "ReadOnly", a special typing construct to mark a
  "TypedDict" item as read-only for type checkers.

* **PEP 742**: Add "TypeIs", a typing construct that can be used to
  instruct a type checker how to narrow a type.

* Add "NoDefault", a sentinel object used to represent the defaults of
  some parameters in the "typing" module. (Contributed by Jelle
  Zijlstra in gh-116126.)

* Add "get_protocol_members()" to return the set of members defining a
  "typing.Protocol". (Contributed by Jelle Zijlstra in gh-104873.)

* Add "is_protocol()" to check whether a class is a "Protocol".
  (Contributed by Jelle Zijlstra in gh-104873.)

* "ClassVar" can now be nested in "Final", and vice versa.
  (Contributed by Mehdi Drissi in gh-89547.)


unicodedata
-----------

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


venv
----

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


warnings
--------

* **PEP 702**: The new "warnings.deprecated()" decorator provides a
  way to communicate deprecations to a *static type 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
  gh-104003.)


xml
---

* Allow controlling Expat >=2.6.0 reparse deferral (**CVE
  2023-52425**) by adding five new methods:

  * "xml.etree.ElementTree.XMLParser.flush()"

  * "xml.etree.ElementTree.XMLPullParser.flush()"

  * "xml.parsers.expat.xmlparser.GetReparseDeferralEnabled()"

  * "xml.parsers.expat.xmlparser.SetReparseDeferralEnabled()"

  * "xml.sax.expatreader.ExpatParser.flush()"

  (Contributed by Sebastian Pipping in gh-115623.)

* Add the "close()" method for the iterator returned by "iterparse()"
  for explicit cleanup. (Contributed by Serhiy Storchaka in gh-69893.)


zipimport
---------

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


Optimizations
=============

* Several standard library modules have had their import times
  significantly improved. For example, the import time of the "typing"
  module has been reduced by around a third by removing dependencies
  on "re" and "contextlib". Other modules to enjoy import-time
  speedups include "email.utils", "enum", "functools",
  "importlib.metadata", and "threading". (Contributed by Alex Waygood,
  Shantanu Jain, Adam Turner, Daniel Hollas, and others in gh-109653.)

* "textwrap.indent()" is now around 30% faster than before for large
  input. (Contributed by Inada Naoki in gh-107369.)

* The "subprocess" module now uses the "posix_spawn()" function in
  more situations, including when *close_fds* is "True" (the default)
  on many modern platforms. This should provide a notable performance
  increase when launching processes on FreeBSD and Solaris. See the
  subprocess section above for details. (Contributed by Jakub Kulik in
  gh-113117.)


Removed Modules And APIs
========================


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

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

* "aifc"

  * standard-aifc: Use the redistribution of "aifc" library from PyPI.

* "audioop"

  * audioop-lts: Use "audioop-lts" library from PyPI.

* "chunk"

  * standard-chunk: Use the redistribution of "chunk" library from
    PyPI.

* "cgi" and "cgitb"

  * "cgi.FieldStorage" can typically be replaced 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 gh-104773 and
gh-104780.)


2to3
----

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


builtins
--------

* Remove support for chained "classmethod" descriptors (introduced in
  gh-63272). These can no longer be used to wrap other descriptors,
  such as "property". The core design of this feature was flawed and
  led to several problems. To "pass-through" a "classmethod", consider
  using the "__wrapped__" attribute that was added in Python 3.10.
  (Contributed by Raymond Hettinger in gh-89519.)

* Raise a "RuntimeError" when calling "frame.clear()" on a suspended
  frame (as has always been the case for an executing frame).
  (Contributed by Irit Katriel in gh-79932.)


configparser
------------

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


importlib.metadata
------------------

* Remove deprecated subscript ("__getitem__()") access for EntryPoint
  objects. (Contributed by Jason R. Coombs in gh-113175.)


locale
------

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


opcode
------

* Move "opcode.ENABLE_SPECIALIZATION" to
  "_opcode.ENABLE_SPECIALIZATION". This field was added in 3.12, it
  was never documented, and is not intended for external use.
  (Contributed by Irit Katriel in gh-105481.)

* Remove "opcode.is_pseudo()", "opcode.MIN_PSEUDO_OPCODE", and
  "opcode.MAX_PSEUDO_OPCODE", which were added in Python 3.12, but
  were neither documented nor exposed through "dis", and were not
  intended to be used externally. (Contributed by Irit Katriel in
  gh-105481.)


optparse
--------

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


pathlib
-------

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


re
--

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


tkinter.tix
-----------

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


turtle
------

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


typing
------

* Remove the "typing.io" and "typing.re" namespaces, deprecated since
  Python 3.8. The items in those namespaces can be imported directly
  from the "typing" module. (Contributed by Sebastian Rittau in
  gh-92871.)

* Remove the keyword-argument method of creating "TypedDict" types,
  deprecated in Python 3.11. (Contributed by Tomas Roun in gh-104786.)


unittest
--------

* Remove the following "unittest" functions, deprecated in Python
  3.11:

  * "unittest.findTestCases()"

  * "unittest.makeSuite()"

  * "unittest.getTestCaseNames()"

  Use "TestLoader" methods instead:

  * "loadTestsFromModule()"

  * "loadTestsFromTestCase()"

  * "getTestCaseNames()"

  (Contributed by Hugo van Kemenade in gh-104835.)

* Remove the untested and undocumented "TestProgram.usageExit()"
  method, deprecated in Python 3.11. (Contributed by Hugo van Kemenade
  in gh-104992.)


urllib
------

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


webbrowser
----------

* Remove the untested and undocumented "MacOSX" class, deprecated in
  Python 3.11. Use the "MacOSXOSAScript" class (introduced in Python
  3.2) instead. (Contributed by Hugo van Kemenade in gh-104804.)

* Remove the deprecated "MacOSXOSAScript._name" attribute. Use the
  "MacOSXOSAScript.name" attribute instead. (Contributed by Nikita
  Sobolev in gh-105546.)


New Deprecations
================

* User-defined functions:

  * Deprecate assignment to a function's "__code__" attribute, where
    the new code object's type does not match the function's type. The
    different types are: plain function, generator, async generator,
    and coroutine. (Contributed by Irit Katriel in gh-81137.)

* "array":

  * Deprecate the "'u'" format code ("wchar_t") at runtime. This
    format code has been deprecated in documentation since Python 3.3,
    and will be removed in Python 3.16. Use the "'w'" format code
    ("Py_UCS4") for Unicode characters instead. (Contributed by Hugo
    van Kemenade in gh-80480.)

* "ctypes":

  * Deprecate the undocumented "SetPointerType()" function, to be
    removed in Python 3.15. (Contributed by Victor Stinner in
    gh-105733.)

  * *Soft-deprecate* the "ARRAY()" function in favour of "type *
    length" multiplication. (Contributed by Victor Stinner in
    gh-105733.)

* "decimal":

  * Deprecate the non-standard and undocumented "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 gh-89902.)

* "dis":

  * Deprecate the "HAVE_ARGUMENT" separator. Check membership in
    "hasarg" instead. (Contributed by Irit Katriel in gh-109319.)

* "gettext":

  * Deprecate non-integer numbers as arguments to functions and
    methods that consider plural forms in the "gettext" module, even
    if no translation was found. (Contributed by Serhiy Storchaka in
    gh-88434.)

* "glob":

  * Deprecate the undocumented "glob0()" and "glob1()" functions. Use
    "glob()" and pass a *path-like object* specifying the root
    directory to the *root_dir* parameter instead. (Contributed by
    Barney Gale in gh-117337.)

* "http.server":

  * Deprecate "CGIHTTPRequestHandler", to be removed in Python 3.15.
    Process-based CGI HTTP servers have been out of favor for a very
    long time. This code was outdated, unmaintained, and rarely used.
    It has a high potential for both security and functionality bugs.
    (Contributed by Gregory P. Smith in gh-109096.)

  * Deprecate the "--cgi" flag to the **python -m http.server**
    command-line interface, to be removed in Python 3.15. (Contributed
    by Gregory P. Smith in gh-109096.)

* "mimetypes":

  * *Soft-deprecate* file path arguments to "guess_type()", use
    "guess_file_type()" instead. (Contributed by Serhiy Storchaka in
    gh-66543.)

* "re":

  * Deprecate passing the optional *maxsplit*, *count*, or *flags*
    arguments as positional arguments to the module-level "split()",
    "sub()", and "subn()" functions. These parameters will become
    keyword-only in a future version of Python. (Contributed by Serhiy
    Storchaka in gh-56166.)

* "pathlib":

  * Deprecate "PurePath.is_reserved()", to be removed in Python 3.15.
    Use "os.path.isreserved()" to detect reserved paths on Windows.
    (Contributed by Barney Gale in gh-88569.)

* "platform":

  * Deprecate "java_ver()", to be removed in Python 3.15. This
    function is only useful for Jython support, has a confusing API,
    and is largely untested. (Contributed by Nikita Sobolev in
    gh-116349.)

* "pydoc":

  * Deprecate the undocumented "ispackage()" function. (Contributed by
    Zackery Spytz in gh-64020.)

* "sqlite3":

  * Deprecate passing more than one positional argument to the
    "connect()" function and the "Connection" constructor. The
    remaining parameters will become keyword-only in Python 3.15.
    (Contributed by Erlend E. Aasland in gh-107948.)

  * Deprecate passing name, number of arguments, and the callable as
    keyword arguments for "Connection.create_function()" and
    "Connection.create_aggregate()" These parameters will become
    positional-only in Python 3.15. (Contributed by Erlend E. Aasland
    in gh-108278.)

  * Deprecate passing the callback callable by keyword for the
    "set_authorizer()", "set_progress_handler()", and
    "set_trace_callback()" "Connection" methods. The callback
    callables will become positional-only in Python 3.15. (Contributed
    by Erlend E. Aasland in gh-108278.)

* "sys":

  * Deprecate the "_enablelegacywindowsfsencoding()" function, to be
    removed in Python 3.16. Use the "PYTHONLEGACYWINDOWSFSENCODING"
    environment variable instead. (Contributed by Inada Naoki in
    gh-73427.)

* "tarfile":

  * Deprecate the undocumented and unused "TarFile.tarfile" attribute,
    to be removed in Python 3.16. (Contributed in gh-115256.)

* "traceback":

  * Deprecate the "TracebackException.exc_type" attribute. Use
    "TracebackException.exc_type_str" instead. (Contributed by Irit
    Katriel in gh-112332.)

* "typing":

  * Deprecate the undocumented keyword argument syntax for creating
    "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
    gh-105566.)

  * Deprecate omitting the *fields* parameter when creating a
    "NamedTuple" or "typing.TypedDict" class, and deprecate passing
    "None" to the *fields* parameter of both types. Python 3.15 will
    require a valid sequence for the *fields* parameter. To create a
    NamedTuple class with zero fields, use "class NT(NamedTuple):
    pass" or "NT = NamedTuple("NT", ())". To create a TypedDict class
    with zero fields, use "class TD(TypedDict): pass" or "TD =
    TypedDict("TD", {})". (Contributed by Alex Waygood in gh-105566
    and gh-105570.)

  * Deprecate the "typing.no_type_check_decorator()" decorator
    function, to be removed in Python 3.15. After eight years in the
    "typing" module, it has yet to be supported by any major type
    checker. (Contributed by Alex Waygood in gh-106309.)

  * Deprecate "typing.AnyStr". In Python 3.16, it will be removed from
    "typing.__all__", and a "DeprecationWarning" will be emitted at
    runtime when it is imported or accessed. It will be removed
    entirely in Python 3.18. Use the new type parameter syntax
    instead. (Contributed by Michael The in gh-107116.)

* "wave":

  * Deprecate the "getmark()", "setmark()", and "getmarkers()" methods
    of the "Wave_read" and "Wave_write" classes, to be removed in
    Python 3.15. (Contributed by Victor Stinner in gh-105096.)


Pending removal in Python 3.14
------------------------------

* "argparse": The *type*, *choices*, and *metavar* parameters of
  "argparse.BooleanOptionalAction" are deprecated and will be removed
  in 3.14. (Contributed by Nikita Sobolev in gh-92248.)

* "ast": The following features have been deprecated in documentation
  since Python 3.8, now cause a "DeprecationWarning" to be emitted at
  runtime when they are accessed or used, and will be removed in
  Python 3.14:

  * "ast.Num"

  * "ast.Str"

  * "ast.Bytes"

  * "ast.NameConstant"

  * "ast.Ellipsis"

  Use "ast.Constant" instead. (Contributed by Serhiy Storchaka in
  gh-90953.)

* "asyncio":

  * The child watcher classes "asyncio.MultiLoopChildWatcher",
    "asyncio.FastChildWatcher", "asyncio.AbstractChildWatcher" and
    "asyncio.SafeChildWatcher" are deprecated and will be removed in
    Python 3.14. (Contributed by Kumar Aditya in gh-94597.)

  * "asyncio.set_child_watcher()", "asyncio.get_child_watcher()",
    "asyncio.AbstractEventLoopPolicy.set_child_watcher()" and
    "asyncio.AbstractEventLoopPolicy.get_child_watcher()" are
    deprecated and will be removed in Python 3.14. (Contributed by
    Kumar Aditya in gh-94597.)

  * The "get_event_loop()" method of the default event loop policy now
    emits a "DeprecationWarning" if there is no current event loop set
    and it decides to create one. (Contributed by Serhiy Storchaka and
    Guido van Rossum in gh-100160.)

* "email": Deprecated the *isdst* parameter in
  "email.utils.localtime()". (Contributed by Alan Williams in
  gh-72346.)

* "importlib.abc" deprecated classes:

  * "importlib.abc.ResourceReader"

  * "importlib.abc.Traversable"

  * "importlib.abc.TraversableResources"

  Use "importlib.resources.abc" classes instead:

  * "importlib.resources.abc.Traversable"

  * "importlib.resources.abc.TraversableResources"

  (Contributed by Jason R. Coombs and Hugo van Kemenade in gh-93963.)

* "itertools" had undocumented, inefficient, historically buggy, and
  inconsistent support for copy, deepcopy, and pickle operations. This
  will be removed in 3.14 for a significant reduction in code volume
  and maintenance burden. (Contributed by Raymond Hettinger in
  gh-101588.)

* "multiprocessing": The default start method will change to a safer
  one on Linux, BSDs, and other non-macOS POSIX platforms where
  "'fork'" is currently the default (gh-84559). Adding a runtime
  warning about this was deemed too disruptive as the majority of code
  is not expected to care. Use the "get_context()" or
  "set_start_method()" APIs to explicitly specify when your code
  *requires* "'fork'".  See Contexts and start methods.

* "pathlib": "is_relative_to()" and "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 gh-97850.)

* "pty":

  * "master_open()": use "pty.openpty()".

  * "slave_open()": use "pty.openpty()".

* "sqlite3":

  * "version" and "version_info".

  * "execute()" and "executemany()" if named placeholders are used and
    *parameters* is a sequence instead of a "dict".

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


Pending removal in Python 3.15
------------------------------

* The import system:

  * Setting "__cached__" on a module while failing to set
    "__spec__.cached" is deprecated. In Python 3.15, "__cached__" will
    cease to be set or take into consideration by the import system or
    standard library. (gh-97879)

  * Setting "__package__" on a module while failing to set
    "__spec__.parent" is deprecated. In Python 3.15, "__package__"
    will cease to be set or take into consideration by the import
    system or standard library. (gh-97879)

* "ctypes":

  * The undocumented "ctypes.SetPointerType()" function has been
    deprecated since Python 3.13.

* "http.server":

  * The obsolete and rarely used "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.

* "locale":

  * The "getdefaultlocale()" function has been deprecated since Python
    3.11. Its removal was originally planned for Python 3.13
    (gh-90817), but has been postponed to Python 3.15. Use
    "getlocale()", "setlocale()", and "getencoding()" instead.
    (Contributed by Hugo van Kemenade in gh-111187.)

* "pathlib":

  * "PurePath.is_reserved()" has been deprecated since Python 3.13.
    Use "os.path.isreserved()" to detect reserved paths on Windows.

* "platform":

  * "java_ver()" has been deprecated since Python 3.13. This function
    is only useful for Jython support, has a confusing API, and is
    largely untested.

* "sysconfig":

  * The *check_home* argument of "sysconfig.is_python_build()" has
    been deprecated since Python 3.12.

* "threading":

  * "RLock()" will take no arguments in Python 3.15. Passing any
    arguments has been deprecated since Python 3.14, as the Python
    version does not permit any arguments, but the C version allows
    any number of positional or keyword arguments, ignoring every
    argument.

* "types":

  * "types.CodeType": Accessing "co_lnotab" was deprecated in **PEP
    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 gh-101866.)

* "typing":

  * The undocumented keyword argument syntax for creating "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 "TypedDict"s, failing to pass
    a value to the *fields* parameter ("TD = TypedDict("TD")") or
    passing "None" ("TD = TypedDict("TD", None)") has been deprecated
    since Python 3.13. Use "class TD(TypedDict): pass" or "TD =
    TypedDict("TD", {})" to create a TypedDict with zero field.

  * The "typing.no_type_check_decorator()" decorator function has been
    deprecated since Python 3.13. After eight years in the "typing"
    module, it has yet to be supported by any major type checker.

* "wave":

  * The "getmark()", "setmark()", and "getmarkers()" methods of the
    "Wave_read" and "Wave_write" classes have been deprecated since
    Python 3.13.

* "zipimport":

  * "load_module()" has been deprecated since Python 3.10. Use
    "exec_module()" instead. (Contributed by Jiahao Li in gh-125746.)


Pending removal in Python 3.16
------------------------------

* The import system:

  * Setting "__loader__" on a module while failing to set
    "__spec__.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.

* "array":

  * The "'u'" format code ("wchar_t") has been deprecated in
    documentation since Python 3.3 and at runtime since Python 3.13.
    Use the "'w'" format code ("Py_UCS4") for Unicode characters
    instead.

* "asyncio":

  * "asyncio.iscoroutinefunction()" is deprecated and will be removed
    in Python 3.16; use "inspect.iscoroutinefunction()" instead.
    (Contributed by Jiahao Li and Kumar Aditya in gh-122875.)

  * "asyncio" policy system is deprecated and will be removed in
    Python 3.16. In particular, the following classes and functions
    are deprecated:

    * "asyncio.AbstractEventLoopPolicy"

    * "asyncio.DefaultEventLoopPolicy"

    * "asyncio.WindowsSelectorEventLoopPolicy"

    * "asyncio.WindowsProactorEventLoopPolicy"

    * "asyncio.get_event_loop_policy()"

    * "asyncio.set_event_loop_policy()"

    Users should use "asyncio.run()" or "asyncio.Runner" with
    *loop_factory* to use the desired event loop implementation.

    For example, to use "asyncio.SelectorEventLoop" on Windows:

       import asyncio

       async def main():
           ...

       asyncio.run(main(), loop_factory=asyncio.SelectorEventLoop)

    (Contributed by Kumar Aditya in gh-127949.)

* "builtins":

  * Bitwise inversion on boolean types, "~True" or "~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 gh-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 gh-75223.)

* "shutil":

  * The "ExecError" exception has been deprecated since Python 3.14.
    It has not been used by any function in "shutil" since Python 3.4,
    and is now an alias of "RuntimeError".

* "symtable":

  * The "Class.get_methods" method has been deprecated since Python
    3.14.

* "sys":

  * The "_enablelegacywindowsfsencoding()" function has been
    deprecated since Python 3.13. Use the
    "PYTHONLEGACYWINDOWSFSENCODING" environment variable instead.

* "sysconfig":

  * The "sysconfig.expand_makefile_vars()" function has been
    deprecated since Python 3.14. Use the "vars" argument of
    "sysconfig.get_paths()" instead.

* "tarfile":

  * The undocumented and unused "TarFile.tarfile" attribute has been
    deprecated since Python 3.13.


Pending removal in Python 3.17
------------------------------

* "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 at runtime. For use in type
    annotations, either use "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** for more details. (Contributed by Shantanu Jain in
    gh-91896.)

* "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 at runtime. For use in type
    annotations, either use "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** for more details. (Contributed by Shantanu Jain in
    gh-91896.)


Pending removal in Python 3.18
------------------------------

* "decimal":

  * The non-standard and undocumented "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 gh-89902.)


Pending removal in Python 3.19
------------------------------

* "ctypes":

  * Implicitly switching to the MSVC-compatible struct layout by
    setting "_pack_" but not "_layout_" on non-Windows platforms.


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
    "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. (gh-87999)

  * Support for "__index__()" and "__int__()" method returning non-int
    type: these methods will be required to return an instance of a
    strict subclass 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".

  * 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 gh-109218.)

* "calendar": "calendar.January" and "calendar.February" constants are
  deprecated and replaced by "calendar.JANUARY" and
  "calendar.FEBRUARY". (Contributed by Prince Roshan in gh-103636.)

* "codecs": use "open()" instead of "codecs.open()". (gh-133038)

* "codeobject.co_lnotab": use the "codeobject.co_lines()" method
  instead.

* "datetime":

  * "utcnow()": use "datetime.datetime.now(tz=datetime.UTC)".

  * "utcfromtimestamp()": use
    "datetime.datetime.fromtimestamp(timestamp, tz=datetime.UTC)".

* "gettext": Plural value must be an integer.

* "importlib":

  * "cache_from_source()" *debug_override* parameter is deprecated:
    use the *optimization* parameter instead.

* "importlib.metadata":

  * "EntryPoints" tuple interface.

  * Implicit "None" on return values.

* "logging": the "warn()" method has been deprecated since Python 3.3,
  use "warning()" instead.

* "mailbox": Use of StringIO input and text mode is deprecated, use
  BytesIO and binary mode instead.

* "os": Calling "os.register_at_fork()" in multi-threaded process.

* "pydoc.ErrorDuringImport": A tuple value for *exc_info* parameter is
  deprecated, use an exception instance.

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

* "sre_compile", "sre_constants" and "sre_parse" modules.

* "shutil": "rmtree()"'s *onerror* parameter is deprecated in Python
  3.12; use the *onexc* parameter instead.

* "ssl" options and protocols:

  * "ssl.SSLContext" without protocol argument is deprecated.

  * "ssl.SSLContext": "set_npn_protocols()" 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 "notify_all()".

  * "threading.Event.isSet()": use "is_set()".

  * "threading.Thread.isDaemon()", "threading.Thread.setDaemon()": use
    "threading.Thread.daemon" attribute.

  * "threading.Thread.getName()", "threading.Thread.setName()": use
    "threading.Thread.name" attribute.

  * "threading.currentThread()": use "threading.current_thread()".

  * "threading.activeCount()": use "threading.active_count()".

* "typing.Text" (gh-92332).

* The internal class "typing._UnionGenericAlias" is no longer used to
  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 gh-105499.)

* "unittest.IsolatedAsyncioTestCase": it is deprecated to return a
  value that is not "None" from a test case.

* "urllib.parse" deprecated functions: "urlparse()" instead

  * "splitattr()"

  * "splithost()"

  * "splitnport()"

  * "splitpasswd()"

  * "splitport()"

  * "splitquery()"

  * "splittag()"

  * "splittype()"

  * "splituser()"

  * "splitvalue()"

  * "to_bytes()"

* "wsgiref": "SimpleHandler.stdout.write()" should not do partial
  writes.

* "xml.etree.ElementTree": Testing the truth value of an "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 gh-111354.)


C API Changes
=============


New Features
------------

* Add the PyMonitoring C API for generating **PEP 669** monitoring
  events:

  * "PyMonitoringState"

  * "PyMonitoring_FirePyStartEvent()"

  * "PyMonitoring_FirePyResumeEvent()"

  * "PyMonitoring_FirePyReturnEvent()"

  * "PyMonitoring_FirePyYieldEvent()"

  * "PyMonitoring_FireCallEvent()"

  * "PyMonitoring_FireLineEvent()"

  * "PyMonitoring_FireJumpEvent()"

  * "PyMonitoring_FireBranchEvent"

  * "PyMonitoring_FireCReturnEvent()"

  * "PyMonitoring_FirePyThrowEvent()"

  * "PyMonitoring_FireRaiseEvent()"

  * "PyMonitoring_FireCRaiseEvent()"

  * "PyMonitoring_FireReraiseEvent()"

  * "PyMonitoring_FireExceptionHandledEvent()"

  * "PyMonitoring_FirePyUnwindEvent()"

  * "PyMonitoring_FireStopIterationEvent()"

  * "PyMonitoring_EnterScope()"

  * "PyMonitoring_ExitScope()"

  (Contributed by Irit Katriel in gh-111997).

* Add "PyMutex", a lightweight mutex that occupies a single byte, and
  the new "PyMutex_Lock()" and "PyMutex_Unlock()" functions.
  "PyMutex_Lock()" will release the *GIL* (if currently held) if the
  operation needs to block. (Contributed by Sam Gross in gh-108724.)

* Add the PyTime C API to provide access to system clocks:

  * "PyTime_t".

  * "PyTime_MIN" and "PyTime_MAX".

  * "PyTime_AsSecondsDouble()".

  * "PyTime_Monotonic()".

  * "PyTime_MonotonicRaw()".

  * "PyTime_PerfCounter()".

  * "PyTime_PerfCounterRaw()".

  * "PyTime_Time()".

  * "PyTime_TimeRaw()".

  (Contributed by Victor Stinner and Petr Viktorin in gh-110850.)

* Add the "PyDict_ContainsString()" function with the same behavior as
  "PyDict_Contains()", but *key* is specified as a const char* UTF-8
  encoded bytes string, rather than a PyObject*. (Contributed by
  Victor Stinner in gh-108314.)

* Add the "PyDict_GetItemRef()" and "PyDict_GetItemStringRef()"
  functions, which behave similarly to "PyDict_GetItemWithError()",
  but return a  *strong reference* instead of a *borrowed reference*.
  Moreover, these functions return "-1" on error, removing the need to
  check "PyErr_Occurred()". (Contributed by Victor Stinner in
  gh-106004.)

* Add the "PyDict_SetDefaultRef()" function, which behaves similarly
  to "PyDict_SetDefault()", but returns a *strong reference* instead
  of a *borrowed reference*. This function returns "-1" on error, "0"
  on insertion, and "1" if the key was already present in the
  dictionary. (Contributed by Sam Gross in gh-112066.)

* Add the "PyDict_Pop()" and "PyDict_PopString()" functions to remove
  a key from a dictionary and optionally return the removed value.
  This is similar to "dict.pop()", though there is no default value,
  and "KeyError" is not raised for missing keys. (Contributed by
  Stefan Behnel and Victor Stinner in gh-111262.)

* Add the "PyMapping_GetOptionalItem()" and
  "PyMapping_GetOptionalItemString()" functions as alternatives to
  "PyObject_GetItem()" and "PyMapping_GetItemString()" respectively.
  The new functions do not raise "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 gh-106307.)

* Add the "PyObject_GetOptionalAttr()" and
  "PyObject_GetOptionalAttrString()" functions as alternatives to
  "PyObject_GetAttr()" and "PyObject_GetAttrString()" respectively.
  The new functions do not raise "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 gh-106521.)

* Add the "PyErr_FormatUnraisable()" function as an extension to
  "PyErr_WriteUnraisable()" that allows customizing the warning
  message. (Contributed by Serhiy Storchaka in gh-108082.)

* Add new functions that return a *strong reference* instead of a
  *borrowed reference* for frame locals, globals, and builtins, as
  part of PEP 667:

  * "PyEval_GetFrameBuiltins()" replaces "PyEval_GetBuiltins()"

  * "PyEval_GetFrameGlobals()" replaces "PyEval_GetGlobals()"

  * "PyEval_GetFrameLocals()" replaces "PyEval_GetLocals()"

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

* Add the "Py_GetConstant()" and "Py_GetConstantBorrowed()" functions
  to get *strong* or *borrowed* references to constants. For example,
  "Py_GetConstant(Py_CONSTANT_ZERO)" returns a strong reference to the
  constant zero. (Contributed by Victor  Stinner in gh-115754.)

* Add the "PyImport_AddModuleRef()" function as a replacement for
  "PyImport_AddModule()" that returns a *strong reference* instead of
  a *borrowed reference*. (Contributed by Victor Stinner in
  gh-105922.)

* Add the "Py_IsFinalizing()" function to check whether the main
  Python interpreter is *shutting down*. (Contributed by Victor
  Stinner in gh-108014.)

* Add the "PyList_GetItemRef()" function as a replacement for
  "PyList_GetItem()" that returns a *strong reference* instead of a
  *borrowed reference*. (Contributed by Sam Gross in gh-114329.)

* Add the "PyList_Extend()" and "PyList_Clear()" functions, mirroring
  the Python "list.extend()" and "list.clear()" methods. (Contributed
  by Victor Stinner in gh-111138.)

* Add the "PyLong_AsInt()" function. It behaves similarly to
  "PyLong_AsLong()", but stores the result in a C int instead of a C
  long. (Contributed by Victor Stinner in gh-108014.)

* Add the "PyLong_AsNativeBytes()", "PyLong_FromNativeBytes()", and
  "PyLong_FromUnsignedNativeBytes()" functions to simplify converting
  between native integer types and Python "int" objects. (Contributed
  by Steve Dower in gh-111140.)

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

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

* Add the "Py_HashPointer()" function to hash a raw pointer.
  (Contributed by Victor Stinner in gh-111545.)

* Add the "PyObject_VisitManagedDict()" 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 gh-107073.)

* Add the "PyRefTracer_SetTracer()" and "PyRefTracer_GetTracer()"
  functions, which enable tracking object creation and destruction in
  the same way that the "tracemalloc" module does. (Contributed by
  Pablo Galindo in gh-93502.)

* Add the "PySys_AuditTuple()" function as an alternative to
  "PySys_Audit()" that takes event arguments as a Python "tuple"
  object. (Contributed by Victor Stinner in gh-85283.)

* Add the "PyThreadState_GetUnchecked()" function as an alternative to
  "PyThreadState_Get()" that doesn't kill the process with a fatal
  error if it is "NULL". The caller is responsible for checking if the
  result is "NULL". (Contributed by Victor Stinner in gh-108867.)

* Add the "PyType_GetFullyQualifiedName()" function to get the type's
  fully qualified name. The module name is prepended if
  "type.__module__" is a string and is not equal to either
  "'builtins'" or "'__main__'". (Contributed by Victor Stinner in
  gh-111696.)

* Add the "PyType_GetModuleName()" function to get the type's module
  name. This is equivalent to getting the "type.__module__" attribute.
  (Contributed by Eric Snow and Victor Stinner in gh-111696.)

* Add the "PyUnicode_EqualToUTF8AndSize()" and
  "PyUnicode_EqualToUTF8()" functions to compare a Unicode object with
  a const char* UTF-8 encoded string and "1" if they are equal or "0"
  otherwise. These functions do not raise exceptions. (Contributed by
  Serhiy Storchaka in gh-110289.)

* Add the "PyWeakref_GetRef()" function as an alternative to
  "PyWeakref_GetObject()" that returns a *strong reference* or "NULL"
  if the referent is no longer live. (Contributed by Victor Stinner in
  gh-105927.)

* Add fixed variants of functions which silently ignore errors:

  * "PyObject_HasAttrWithError()" replaces "PyObject_HasAttr()".

  * "PyObject_HasAttrStringWithError()" replaces
    "PyObject_HasAttrString()".

  * "PyMapping_HasKeyWithError()" replaces "PyMapping_HasKey()".

  * "PyMapping_HasKeyStringWithError()" replaces
    "PyMapping_HasKeyString()".

  The new functions return "-1" for errors and the standard "1" for
  true and "0" for false.

  (Contributed by Serhiy Storchaka in gh-108511.)


Changed C APIs
--------------

* The *keywords* parameter of "PyArg_ParseTupleAndKeywords()" and
  "PyArg_VaParseTupleAndKeywords()" now has type char *const* in C and
  const char *const* in C++, instead of char**. In C++, this makes
  these functions compatible with arguments of type const char
  *const*, const char**, or char *const* without an explicit type
  cast. In C, the functions only support arguments of type char
  *const*. This can be overridden with the "PY_CXX_CONST" macro.
  (Contributed by Serhiy Storchaka in gh-65210.)

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

* The "PyCode_GetFirstFree()" function is now unstable API and is now
  named "PyUnstable_Code_GetFirstFree()". (Contributed by Bogdan
  Romanyuk in gh-115781.)

* The "PyDict_GetItem()", "PyDict_GetItemString()",
  "PyMapping_HasKey()", "PyMapping_HasKeyString()",
  "PyObject_HasAttr()", "PyObject_HasAttrString()", and
  "PySys_GetObject()" functions, each of which clears all errors which
  occurred when calling them now reports these errors using
  "sys.unraisablehook()". You may replace them with other functions as
  recommended in the documentation. (Contributed by Serhiy Storchaka
  in gh-106672.)

* Add support for the "%T", "%#T", "%N" and "%#N" formats to
  "PyUnicode_FromFormat()":

  * "%T": Get the fully qualified name of an object type

  * "%#T": As above, but use a colon as the separator

  * "%N": Get the fully qualified name of a type

  * "%#N": As above, but use a colon as the separator

  See **PEP 737** for more information. (Contributed by Victor Stinner
  in gh-111696.)

* You no longer have to define the "PY_SSIZE_T_CLEAN" macro before
  including "Python.h" when using "#" formats in format codes. APIs
  accepting the format codes always use "Py_ssize_t" for "#" formats.
  (Contributed by Inada Naoki in gh-104922.)

* If Python is built in debug mode or "with assertions",
  "PyTuple_SET_ITEM()" and "PyList_SET_ITEM()" now check the index
  argument with an assertion. (Contributed by Victor Stinner in
  gh-106168.)


Limited C API Changes
---------------------

* The following functions are now included in the Limited C API:

  * "PyMem_RawMalloc()"

  * "PyMem_RawCalloc()"

  * "PyMem_RawRealloc()"

  * "PyMem_RawFree()"

  * "PySys_Audit()"

  * "PySys_AuditTuple()"

  * "PyType_GetModuleByDef()"

  (Contributed by Victor Stinner in gh-85283 and gh-116936.)

* Python built with "--with-trace-refs" (tracing references) now
  supports the Limited API. (Contributed by Victor Stinner in
  gh-108634.)


Removed C APIs
--------------

* Remove several functions, macros, variables, etc with names prefixed
  by "_Py" or "_PY" (which are considered private). If your project is
  affected  by one of these removals and you believe that the removed
  API should remain available, please open a new issue to request a
  public C API and add "cc: @vstinner" to the issue to notify Victor
  Stinner. (Contributed by Victor Stinner in gh-106320.)

* Remove old buffer protocols deprecated in Python 3.0. Use Buffer
  Protocol instead.

  * "PyObject_CheckReadBuffer()": Use "PyObject_CheckBuffer()" to test
    whether the object supports the buffer protocol. Note that
    "PyObject_CheckBuffer()" doesn't guarantee that
    "PyObject_GetBuffer()" will succeed. To test if the object is
    actually readable, see the next example of "PyObject_GetBuffer()".

  * "PyObject_AsCharBuffer()", "PyObject_AsReadBuffer()": Use
    "PyObject_GetBuffer()" and "PyBuffer_Release()" instead:

       Py_buffer view;
       if (PyObject_GetBuffer(obj, &view, PyBUF_SIMPLE) < 0) {
           return NULL;
       }
       // Use `view.buf` and `view.len` to read from the buffer.
       // You may need to cast buf as `(const char*)view.buf`.
       PyBuffer_Release(&view);

  * "PyObject_AsWriteBuffer()": Use "PyObject_GetBuffer()" and
    "PyBuffer_Release()" instead:

       Py_buffer view;
       if (PyObject_GetBuffer(obj, &view, PyBUF_WRITABLE) < 0) {
           return NULL;
       }
       // Use `view.buf` and `view.len` to write to the buffer.
       PyBuffer_Release(&view);

  (Contributed by Inada Naoki in gh-85275.)

* Remove various functions deprecated in Python 3.9:

  * "PyEval_CallObject()", "PyEval_CallObjectWithKeywords()": Use
    "PyObject_CallNoArgs()" or "PyObject_Call()" instead.

    Warning:

      In "PyObject_Call()", positional arguments must be a "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)".

  * "PyEval_CallFunction()": Use "PyObject_CallFunction()" instead.

  * "PyEval_CallMethod()": Use "PyObject_CallMethod()" instead.

  * "PyCFunction_Call()": Use "PyObject_Call()" instead.

  (Contributed by Victor Stinner in gh-105107.)

* Remove the following old functions to configure the Python
  initialization, deprecated in Python 3.11:

  * "PySys_AddWarnOptionUnicode()": Use "PyConfig.warnoptions"
    instead.

  * "PySys_AddWarnOption()": Use "PyConfig.warnoptions" instead.

  * "PySys_AddXOption()": Use "PyConfig.xoptions" instead.

  * "PySys_HasWarnOptions()": Use "PyConfig.xoptions" instead.

  * "PySys_SetPath()": Set "PyConfig.module_search_paths" instead.

  * "Py_SetPath()": Set "PyConfig.module_search_paths" instead.

  * "Py_SetStandardStreamEncoding()": Set "PyConfig.stdio_encoding"
    instead, and set also maybe "PyConfig.legacy_windows_stdio" (on
    Windows).

  * "_Py_SetProgramFullPath()": Set "PyConfig.executable" instead.

  Use the new "PyConfig" API of the Python Initialization
  Configuration instead (**PEP 587**), added to Python 3.8.
  (Contributed by Victor Stinner in gh-105145.)

* Remove "PyEval_AcquireLock()" and "PyEval_ReleaseLock()" functions,
  deprecated in Python 3.2. They didn't update the current thread
  state. They can be replaced with:

  * "PyEval_SaveThread()" and "PyEval_RestoreThread()";

  * low-level "PyEval_AcquireThread()" and "PyEval_RestoreThread()";

  * or "PyGILState_Ensure()" and "PyGILState_Release()".

  (Contributed by Victor Stinner in gh-105182.)

* Remove the "PyEval_ThreadsInitialized()" function, deprecated in
  Python 3.9. Since Python 3.7, "Py_Initialize()" always creates the
  GIL: calling "PyEval_InitThreads()" does nothing and
  "PyEval_ThreadsInitialized()" always returns non-zero. (Contributed
  by Victor Stinner in gh-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 gh-106320.)

* Remove the private "_PyObject_FastCall()" function: use
  "PyObject_Vectorcall()" which is available since Python 3.8 (**PEP
  590**). (Contributed by Victor Stinner in gh-106023.)

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

* Remove the undocumented "PY_TIMEOUT_MAX" constant from the limited C
  API. (Contributed by Victor Stinner in gh-110014.)

* Remove the old trashcan macros "Py_TRASHCAN_SAFE_BEGIN" and
  "Py_TRASHCAN_SAFE_END". Replace both with the new macros
  "Py_TRASHCAN_BEGIN" and "Py_TRASHCAN_END". (Contributed by Irit
  Katriel in gh-105111.)


Deprecated C APIs
-----------------

* Deprecate old Python initialization functions:

  * "PySys_ResetWarnOptions()": Clear "sys.warnoptions" and
    "warnings.filters" instead.

  * "Py_GetExecPrefix()": Get "sys.exec_prefix" instead.

  * "Py_GetPath()": Get "sys.path" instead.

  * "Py_GetPrefix()": Get "sys.prefix" instead.

  * "Py_GetProgramFullPath()": Get "sys.executable" instead.

  * "Py_GetProgramName()": Get "sys.executable" instead.

  * "Py_GetPythonHome()": Get "PyConfig.home" or the "PYTHONHOME"
    environment variable instead.

  (Contributed by Victor Stinner in gh-105145.)

* *Soft deprecate* the "PyEval_GetBuiltins()", "PyEval_GetGlobals()",
  and "PyEval_GetLocals()" functions, which return a *borrowed
  reference*. (Soft deprecated as part of **PEP 667**.)

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

* *Soft deprecate* the "PyModule_AddObject()" function. It should be
  replaced with "PyModule_Add()" or "PyModule_AddObjectRef()".
  (Contributed by Serhiy Storchaka in gh-86493.)

* Deprecate the old "Py_UNICODE" and "PY_UNICODE_TYPE" types and the
  "Py_UNICODE_WIDE" define. Use the "wchar_t" type directly instead.
  Since Python 3.3, "Py_UNICODE" and "PY_UNICODE_TYPE" are just
  aliases to "wchar_t". (Contributed by Victor Stinner in gh-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 gh-105927.)


Pending removal in Python 3.14
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* The "ma_version_tag" field in "PyDictObject" for extension modules
  (**PEP 699**; gh-101193).

* Creating "immutable types" with mutable bases (gh-95388).


Pending removal in Python 3.15
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* The "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.

* "Py_UNICODE" type and the "Py_UNICODE_WIDE" macro: Use "wchar_t"
  instead.

* "PyUnicode_AsDecodedObject()": Use "PyCodec_Decode()" instead.

* "PyUnicode_AsDecodedUnicode()": Use "PyCodec_Decode()" instead; Note
  that some codecs (for example, "base64") may return a type other
  than "str", such as "bytes".

* "PyUnicode_AsEncodedObject()": Use "PyCodec_Encode()" instead.

* "PyUnicode_AsEncodedUnicode()": Use "PyCodec_Encode()" instead; Note
  that some codecs (for example, "base64") may return a type other
  than "bytes", such as "str".

* Python initialization functions, deprecated in Python 3.13:

  * "Py_GetPath()": Use "PyConfig_Get("module_search_paths")"
    ("sys.path") instead.

  * "Py_GetPrefix()": Use "PyConfig_Get("base_prefix")"
    ("sys.base_prefix") instead. Use "PyConfig_Get("prefix")"
    ("sys.prefix") if virtual environments need to be handled.

  * "Py_GetExecPrefix()": Use "PyConfig_Get("base_exec_prefix")"
    ("sys.base_exec_prefix") instead. Use
    "PyConfig_Get("exec_prefix")" ("sys.exec_prefix") if virtual
    environments need to be handled.

  * "Py_GetProgramFullPath()": Use "PyConfig_Get("executable")"
    ("sys.executable") instead.

  * "Py_GetProgramName()": Use "PyConfig_Get("executable")"
    ("sys.executable") instead.

  * "Py_GetPythonHome()": Use "PyConfig_Get("home")" or the
    "PYTHONHOME" environment variable instead.

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

* Functions to configure Python's initialization, deprecated in Python
  3.11:

  * "PySys_SetArgvEx()": Set "PyConfig.argv" instead.

  * "PySys_SetArgv()": Set "PyConfig.argv" instead.

  * "Py_SetProgramName()": Set "PyConfig.program_name" instead.

  * "Py_SetPythonHome()": Set "PyConfig.home" instead.

  * "PySys_ResetWarnOptions()": Clear "sys.warnoptions" and
    "warnings.filters" instead.

  The "Py_InitializeFromConfig()" API should be used with "PyConfig"
  instead.

* Global configuration variables:

  * "Py_DebugFlag": Use "PyConfig.parser_debug" or
    "PyConfig_Get("parser_debug")" instead.

  * "Py_VerboseFlag": Use "PyConfig.verbose" or
    "PyConfig_Get("verbose")" instead.

  * "Py_QuietFlag": Use "PyConfig.quiet" or "PyConfig_Get("quiet")"
    instead.

  * "Py_InteractiveFlag": Use "PyConfig.interactive" or
    "PyConfig_Get("interactive")" instead.

  * "Py_InspectFlag": Use "PyConfig.inspect" or
    "PyConfig_Get("inspect")" instead.

  * "Py_OptimizeFlag": Use "PyConfig.optimization_level" or
    "PyConfig_Get("optimization_level")" instead.

  * "Py_NoSiteFlag": Use "PyConfig.site_import" or
    "PyConfig_Get("site_import")" instead.

  * "Py_BytesWarningFlag": Use "PyConfig.bytes_warning" or
    "PyConfig_Get("bytes_warning")" instead.

  * "Py_FrozenFlag": Use "PyConfig.pathconfig_warnings" or
    "PyConfig_Get("pathconfig_warnings")" instead.

  * "Py_IgnoreEnvironmentFlag": Use "PyConfig.use_environment" or
    "PyConfig_Get("use_environment")" instead.

  * "Py_DontWriteBytecodeFlag": Use "PyConfig.write_bytecode" or
    "PyConfig_Get("write_bytecode")" instead.

  * "Py_NoUserSiteDirectory": Use "PyConfig.user_site_directory" or
    "PyConfig_Get("user_site_directory")" instead.

  * "Py_UnbufferedStdioFlag": Use "PyConfig.buffered_stdio" or
    "PyConfig_Get("buffered_stdio")" instead.

  * "Py_HashRandomizationFlag": Use "PyConfig.use_hash_seed" and
    "PyConfig.hash_seed" or "PyConfig_Get("hash_seed")" instead.

  * "Py_IsolatedFlag": Use "PyConfig.isolated" or
    "PyConfig_Get("isolated")" instead.

  * "Py_LegacyWindowsFSEncodingFlag": Use
    "PyPreConfig.legacy_windows_fs_encoding" or
    "PyConfig_Get("legacy_windows_fs_encoding")" instead.

  * "Py_LegacyWindowsStdioFlag": Use "PyConfig.legacy_windows_stdio"
    or "PyConfig_Get("legacy_windows_stdio")" instead.

  * "Py_FileSystemDefaultEncoding", "Py_HasFileSystemDefaultEncoding":
    Use "PyConfig.filesystem_encoding" or
    "PyConfig_Get("filesystem_encoding")" instead.

  * "Py_FileSystemDefaultEncodeErrors": Use
    "PyConfig.filesystem_errors" or
    "PyConfig_Get("filesystem_errors")" instead.

  * "Py_UTF8Mode": Use "PyPreConfig.utf8_mode" or
    "PyConfig_Get("utf8_mode")" 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.


Pending removal in Python 3.16
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* The bundled copy of "libmpdec".


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_Finish()": replace
    "_PyUnicodeWriter_Finish(&writer)" with
    "PyUnicodeWriter_Finish(writer)".

  * "_PyUnicodeWriter_Dealloc()": replace
    "_PyUnicodeWriter_Dealloc(&writer)" with
    "PyUnicodeWriter_Discard(writer)".

  * "_PyUnicodeWriter_WriteChar()": replace
    "_PyUnicodeWriter_WriteChar(&writer, ch)" with
    "PyUnicodeWriter_WriteChar(writer, ch)".

  * "_PyUnicodeWriter_WriteStr()": replace
    "_PyUnicodeWriter_WriteStr(&writer, str)" with
    "PyUnicodeWriter_WriteStr(writer, str)".

  * "_PyUnicodeWriter_WriteSubstring()": replace
    "_PyUnicodeWriter_WriteSubstring(&writer, str, start, end)" with
    "PyUnicodeWriter_WriteSubstring(writer, str, start, end)".

  * "_PyUnicodeWriter_WriteASCIIString()": replace
    "_PyUnicodeWriter_WriteASCIIString(&writer, str)" with
    "PyUnicodeWriter_WriteASCII(writer, str)".

  * "_PyUnicodeWriter_WriteLatin1String()": replace
    "_PyUnicodeWriter_WriteLatin1String(&writer, str)" with
    "PyUnicodeWriter_WriteUTF8(writer, str)".

  * "_PyUnicodeWriter_Prepare()": (no replacement).

  * "_PyUnicodeWriter_PrepareKind()": (no replacement).

  * "_Py_HashPointer()": use "Py_HashPointer()".

  * "_Py_fopen_obj()": use "Py_fopen()".

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

* "PyModule_GetFilename()": Use "PyModule_GetFilenameObject()"
  instead.

* "PyOS_AfterFork()": Use "PyOS_AfterFork_Child()" instead.

* "PySlice_GetIndicesEx()": Use "PySlice_Unpack()" and
  "PySlice_AdjustIndices()" instead.

* "PyUnicode_READY()": Unneeded since Python 3.12

* "PyErr_Display()": Use "PyErr_DisplayException()" instead.

* "_PyErr_ChainExceptions()": Use "_PyErr_ChainExceptions1()" instead.

* "PyBytesObject.ob_shash" member: call "PyObject_Hash()" instead.

* Thread Local Storage (TLS) API:

  * "PyThread_create_key()": Use "PyThread_tss_alloc()" instead.

  * "PyThread_delete_key()": Use "PyThread_tss_free()" instead.

  * "PyThread_set_key_value()": Use "PyThread_tss_set()" instead.

  * "PyThread_get_key_value()": Use "PyThread_tss_get()" instead.

  * "PyThread_delete_key_value()": Use "PyThread_tss_delete()"
    instead.

  * "PyThread_ReInitTLS()": Unneeded since Python 3.7.


Build Changes
=============

* "arm64-apple-ios" and "arm64-apple-ios-simulator" are both now **PEP
  11** tier 3 platforms. (PEP 730 written and implementation
  contributed by Russell Keith-Magee in gh-114099.)

* "aarch64-linux-android" and "x86_64-linux-android" are both now
  **PEP 11** tier 3 platforms. (PEP 738 written and implementation
  contributed by Malcolm Smith in gh-116622.)

* "wasm32-wasi" is now a **PEP 11** tier 2 platform. (Contributed by
  Brett Cannon in gh-115192.)

* "wasm32-emscripten" is no longer a **PEP 11** supported platform.
  (Contributed by Brett Cannon in gh-115192.)

* Building CPython now requires a compiler with support for the C11
  atomic library, GCC built-in atomic functions, or MSVC interlocked
  intrinsics.

* Autoconf 2.71 and aclocal 1.16.5 are now required to regenerate the
  "configure" script. (Contributed by Christian Heimes in gh-89886 and
  by Victor Stinner in gh-112090.)

* SQLite 3.15.2 or newer is required to build the "sqlite3" extension
  module. (Contributed by Erlend Aasland in gh-105875.)

* CPython now bundles the mimalloc library by default. It is licensed
  under the MIT license; see mimalloc license. The bundled mimalloc
  has custom changes, see gh-113141 for details. (Contributed by Dino
  Viehland in gh-109914.)

* The "configure" option "--with-system-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. (Contributed by Victor Stinner in gh-108634.)

* On POSIX systems, the pkg-config (".pc") filenames now include the
  ABI flags.  For example, the free-threaded build generates
  "python-3.13t.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. (Contributed by Victor Stinner in gh-85283.)


Porting to Python 3.13
======================

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


Changes in the Python API
-------------------------

* PEP 667 introduces several changes to the semantics of "locals()"
  and "f_locals":

  * Calling "locals()" in an *optimized scope* now produces an
    independent snapshot on each call, and hence no longer implicitly
    updates previously returned references. Obtaining the legacy
    CPython behavior now requires explicit calls to update the
    initially returned dictionary with the results of subsequent calls
    to "locals()". Code execution functions that implicitly target
    "locals()" (such as "exec" and "eval") must be passed an explicit
    namespace to access their results in an optimized scope. (Changed
    as part of **PEP 667**.)

  * Calling "locals()" from a comprehension at module or class scope
    (including via "exec" or "eval") once more behaves as if the
    comprehension were running as an independent nested function (i.e.
    the local variables from the containing scope are not included).
    In Python 3.12, this had changed to include the local variables
    from the containing scope when implementing **PEP 709**. (Changed
    as part of **PEP 667**.)

  * Accessing "FrameType.f_locals" in an *optimized scope* now returns
    a write-through proxy rather than a snapshot that gets updated at
    ill-specified times. If a snapshot is desired, it must be created
    explicitly with "dict" or the proxy's ".copy()" method. (Changed
    as part of **PEP 667**.)

* "functools.partial" now emits a "FutureWarning" when used as a
  method. The behavior will change in future Python versions. Wrap it
  in "staticmethod()" if you want to preserve the old behavior.
  (Contributed by Serhiy Storchaka in gh-121027.)

* An "OSError" is now raised by "getpass.getuser()" for any failure to
  retrieve a username, instead of "ImportError" on non-Unix platforms
  or "KeyError" on Unix platforms where the password database is
  empty.

* The value of the "mode" attribute of "gzip.GzipFile" is now a string
  ("'rb'" or "'wb'") instead of an integer ("1" or "2"). The value of
  the "mode" attribute of the readable file-like object returned by
  "zipfile.ZipFile.open()" is now "'rb'" instead of "'r'".
  (Contributed by Serhiy Storchaka in gh-115961.)

* "mailbox.Maildir" now ignores files with a leading dot (".").
  (Contributed by Zackery Spytz in gh-65559.)

* "pathlib.Path.glob()" and "rglob()" now return both files and
  directories if a pattern that ends with ""**"" is given, rather than
  directories only. Add a trailing slash to keep the previous behavior
  and only match directories.

* The "threading" module now expects the "_thread" module to have an
  "_is_main_interpreter()" function. This function takes no arguments
  and returns "True" if the current interpreter is the main
  interpreter.

  Any library or application that provides a custom "_thread" module
  must provide "_is_main_interpreter()", just like the module's other
  "private" attributes. (gh-112826.)


Changes in the C API
--------------------

* "Python.h" no longer includes the "<ieeefp.h>" standard header. It
  was included for the "finite()" function which is now provided by
  the "<math.h>" header. It should now be included explicitly if
  needed. Remove also the "HAVE_IEEEFP_H" macro. (Contributed by
  Victor Stinner in gh-108765.)

* "Python.h" no longer includes these standard header files:
  "<time.h>", "<sys/select.h>" and "<sys/time.h>". If needed, they
  should now be included explicitly. For example, "<time.h>" provides
  the "clock()" 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 gh-108765.)

* On Windows, "Python.h" no longer includes the "<stddef.h>" standard
  header file. If needed, it should now be included explicitly. For
  example, it provides "offsetof()" function, and "size_t" and
  "ptrdiff_t" types. Including "<stddef.h>" explicitly was already
  needed by all other platforms, the "HAVE_STDDEF_H" macro is only
  defined on Windows. (Contributed by Victor Stinner in gh-108765.)

* If the "Py_LIMITED_API" macro is defined, "Py_BUILD_CORE",
  "Py_BUILD_CORE_BUILTIN" and "Py_BUILD_CORE_MODULE" macros are now
  undefined by "<Python.h>". (Contributed by Victor Stinner in
  gh-85283.)

* The old trashcan macros "Py_TRASHCAN_SAFE_BEGIN" and
  "Py_TRASHCAN_SAFE_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
     }

  should migrate to the new macros as follows:

     static void
     mytype_dealloc(mytype *p)
     {
         PyObject_GC_UnTrack(p);
         Py_TRASHCAN_BEGIN(p, mytype_dealloc)
         ...
         Py_TRASHCAN_END
     }

  Note that "Py_TRASHCAN_BEGIN" has a second argument which should be
  the deallocation function it is in. The new macros were added in
  Python 3.8 and the old macros were deprecated in Python 3.11.
  (Contributed by Irit Katriel in gh-105111.)

* PEP 667 introduces several changes to frame-related functions:

  * The effects of mutating the dictionary returned from
    "PyEval_GetLocals()" in an *optimized scope* have changed. New
    dict entries added this way will now *only* be visible to
    subsequent "PyEval_GetLocals()" calls in that frame, as
    "PyFrame_GetLocals()", "locals()", and "FrameType.f_locals" no
    longer access the same underlying cached dictionary. Changes made
    to entries for actual variable names and names added via the
    write-through proxy interfaces will be overwritten on subsequent
    calls to "PyEval_GetLocals()" in that frame. The recommended code
    update depends on how the function was being used, so refer to the
    deprecation notice on the function for details.

  * Calling "PyFrame_GetLocals()" in an *optimized scope* now returns
    a write-through proxy rather than a snapshot that gets updated at
    ill-specified times. If a snapshot is desired, it must be created
    explicitly (e.g. with "PyDict_Copy()"), or by calling the new
    "PyEval_GetFrameLocals()" API.

  * "PyFrame_FastToLocals()" and "PyFrame_FastToLocalsWithError()" no
    longer have any effect. Calling these functions has been redundant
    since Python 3.11, when "PyFrame_GetLocals()" was first
    introduced.

  * "PyFrame_LocalsToFast()" no longer has any effect. Calling this
    function is redundant now that "PyFrame_GetLocals()" returns a
    write-through proxy for *optimized scopes*.

* Python 3.13 removed many private functions. Some of them can be
  replaced using these alternatives:

  * "_PyDict_Pop()": "PyDict_Pop()" or "PyDict_PopString()";

  * "_PyDict_GetItemWithError()": "PyDict_GetItemRef()";

  * "_PyErr_WriteUnraisableMsg()":  "PyErr_FormatUnraisable()";

  * "_PyEval_SetTrace()": "PyEval_SetTrace()" or
    "PyEval_SetTraceAllThreads()";

  * "_PyList_Extend()": "PyList_Extend()";

  * "_PyLong_AsInt()": "PyLong_AsInt()";

  * "_PyMem_RawStrdup()": "strdup()";

  * "_PyMem_Strdup()": "strdup()";

  * "_PyObject_ClearManagedDict()": "PyObject_ClearManagedDict()";

  * "_PyObject_VisitManagedDict()": "PyObject_VisitManagedDict()";

  * "_PyThreadState_UncheckedGet()": "PyThreadState_GetUnchecked()";

  * "_PyTime_AsSecondsDouble()": "PyTime_AsSecondsDouble()";

  * "_PyTime_GetMonotonicClock()": "PyTime_Monotonic()" or
    "PyTime_MonotonicRaw()";

  * "_PyTime_GetPerfCounter()": "PyTime_PerfCounter()" or
    "PyTime_PerfCounterRaw()";

  * "_PyTime_GetSystemClock()": "PyTime_Time()" or "PyTime_TimeRaw()";

  * "_PyTime_MAX": "PyTime_MAX";

  * "_PyTime_MIN": "PyTime_MIN";

  * "_PyTime_t": "PyTime_t";

  * "_Py_HashPointer()": "Py_HashPointer()";

  * "_Py_IsFinalizing()": "Py_IsFinalizing()".

  The pythoncapi-compat project can be used to get most of these new
  functions on Python 3.12 and older.


Regression Test Changes
=======================

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