
****************************
  What's New In Python 3.12
****************************

:Editor: Adam Turner

.. Rules for maintenance:

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

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

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

   * If you want to draw your new text to the attention of the
   maintainer, add 'XXX' to the beginning of the paragraph or
   section.

   * It's OK to just add a fragmentary note about a change.  For
   example: "XXX Describe the transmogrify() function added to the
   socket module."  The maintainer will research the change and
   write the necessary text.

   * You can comment out your additions if you like, but it's not
   necessary (especially when a final release is some months away).

   * Credit the author of a patch or bugfix.   Just the name is
   sufficient; the e-mail address isn't necessary.

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

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

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

This article explains the new features in Python 3.12, compared to 3.11.
Python 3.12 was released on October 2, 2023.
For full details, see the :ref:`changelog <changelog>`.

.. seealso::

   :pep:`693` -- Python 3.12 Release Schedule

Summary -- Release highlights
=============================

.. This section singles out the most important changes in Python 3.12.
   Brevity is key.

Python 3.12 is the latest stable release of the Python programming language,
with a mix of changes to the language and the standard library.
The library changes focus on cleaning up deprecated APIs, usability, and correctness.
Of note, the :mod:`!distutils` package has been removed from the standard library.
Filesystem support in :mod:`os` and :mod:`pathlib` has seen a number of improvements,
and several modules have better performance.

The language changes focus on usability,
as :term:`f-strings <f-string>` have had many limitations removed
and 'Did you mean ...' suggestions continue to improve.
The new :ref:`type parameter syntax <whatsnew312-pep695>`
and :keyword:`type` statement improve ergonomics for using :term:`generic types
<generic type>` and :term:`type aliases <type alias>` with static type checkers.

This article doesn't attempt to provide a complete specification of all new features,
but instead gives a convenient overview.
For full details, you should refer to the documentation,
such as the  :ref:`Library Reference <library-index>`
and :ref:`Language Reference <reference-index>`.
If you want 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.

--------------

.. PEP-sized items next.

New syntax features:

* :ref:`PEP 695 <whatsnew312-pep695>`, type parameter syntax and the :keyword:`type` statement

New grammar features:

* :ref:`PEP 701 <whatsnew312-pep701>`, :term:`f-strings <f-string>` in the grammar

Interpreter improvements:

* :ref:`PEP 684 <whatsnew312-pep684>`, a unique per-interpreter :term:`GIL
  <global interpreter lock>`
* :ref:`PEP 669 <whatsnew312-pep669>`, low impact monitoring
* `Improved 'Did you mean ...' suggestions <improved error messages_>`_
  for :exc:`NameError`, :exc:`ImportError`, and :exc:`SyntaxError` exceptions

Python data model improvements:

* :ref:`PEP 688 <whatsnew312-pep688>`, using the :ref:`buffer protocol
  <bufferobjects>` from Python

Significant improvements in the standard library:

* The :class:`pathlib.Path` class now supports subclassing
* The :mod:`os` module received several improvements for Windows support
* A :ref:`command-line interface <sqlite3-cli>` has been added to the
  :mod:`sqlite3` module
* :func:`isinstance` checks against :func:`runtime-checkable protocols
  <typing.runtime_checkable>` enjoy a speed up of between two and 20 times
* The :mod:`asyncio` package has had a number of performance improvements,
  with some benchmarks showing a 75% speed up.
* A :ref:`command-line interface <uuid-cli>` has been added to the
  :mod:`uuid` module
* Due to the changes in :ref:`PEP 701 <whatsnew312-pep701>`,
  producing tokens via the :mod:`tokenize` module is up to 64% faster.

Security improvements:

* Replace the builtin :mod:`hashlib` implementations of
  SHA1, SHA3, SHA2-384, SHA2-512, and MD5 with formally verified code from the
  `HACL* <https://github.com/hacl-star/hacl-star/>`__ project.
  These builtin implementations remain as fallbacks that are only used when
  OpenSSL does not provide them.

C API improvements:

* :ref:`PEP 697 <whatsnew312-pep697>`, unstable C API tier
* :ref:`PEP 683 <whatsnew312-pep683>`, immortal objects

CPython implementation improvements:

* :ref:`PEP 709 <whatsnew312-pep709>`, comprehension inlining
* :ref:`CPython support <perf_profiling>` for the Linux ``perf`` profiler
* Implement stack overflow protection on supported platforms

New typing features:

* :ref:`PEP 692 <whatsnew312-pep692>`, using :class:`~typing.TypedDict` to
  annotate :term:`**kwargs <argument>`
* :ref:`PEP 698 <whatsnew312-pep698>`, :func:`typing.override` decorator

Important deprecations, removals or restrictions:

* :pep:`623`: Remove ``wstr`` from Unicode objects in Python's C API,
  reducing the size of every :class:`str` object by at least 8 bytes.

* :pep:`632`: Remove the :mod:`!distutils` package.
  See `the migration guide <https://peps.python.org/pep-0632/#migration-advice>`_
  for advice replacing the APIs it provided.
  The third-party `Setuptools <https://setuptools.pypa.io/en/latest/deprecated/distutils-legacy.html>`__
  package continues to provide :mod:`!distutils`,
  if you still require it in Python 3.12 and beyond.

* :gh:`95299`: Do not pre-install ``setuptools`` in virtual environments
  created with :mod:`venv`.
  This means that ``distutils``, ``setuptools``, ``pkg_resources``,
  and ``easy_install`` will no longer available by default; to access these
  run ``pip install setuptools`` in the :ref:`activated <venv-explanation>`
  virtual environment.

* The :mod:`!asynchat`, :mod:`!asyncore`, and :mod:`!imp` modules have been
  removed, along with several :class:`unittest.TestCase`
  `method aliases <unittest-TestCase-removed-aliases_>`_.


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

.. _whatsnew312-pep695:

PEP 695: Type Parameter Syntax
------------------------------

Generic classes and functions under :pep:`484` were declared using a verbose syntax
that left the scope of type parameters unclear and required explicit declarations of
variance.

:pep:`695` introduces a new, more compact and explicit way to create
:ref:`generic classes <generic-classes>` and :ref:`functions <generic-functions>`::

   def max[T](args: Iterable[T]) -> T:
       ...

   class list[T]:
       def __getitem__(self, index: int, /) -> T:
           ...

       def append(self, element: T) -> None:
           ...

In addition, the PEP introduces a new way to declare :ref:`type aliases <type-aliases>`
using the :keyword:`type` statement, which creates an instance of
:class:`~typing.TypeAliasType`::

   type Point = tuple[float, float]

Type aliases can also be :ref:`generic <generic-type-aliases>`::

   type Point[T] = tuple[T, T]

The new syntax allows declaring :class:`~typing.TypeVarTuple`
and :class:`~typing.ParamSpec` parameters, as well as :class:`~typing.TypeVar`
parameters with bounds or constraints::

   type IntFunc[**P] = Callable[P, int]  # ParamSpec
   type LabeledTuple[*Ts] = tuple[str, *Ts]  # TypeVarTuple
   type HashableSequence[T: Hashable] = Sequence[T]  # TypeVar with bound
   type IntOrStrSequence[T: (int, str)] = Sequence[T]  # TypeVar with constraints

The value of type aliases and the bound and constraints of type variables
created through this syntax are evaluated only on demand (see
:ref:`lazy evaluation <lazy-evaluation>`). This means type aliases are able to
refer to other types defined later in the file.

Type parameters declared through a type parameter list are visible within the
scope of the declaration and any nested scopes, but not in the outer scope. For
example, they can be used in the type annotations for the methods of a generic
class or in the class body. However, they cannot be used in the module scope after
the class is defined. See :ref:`type-params` for a detailed description of the
runtime semantics of type parameters.

In order to support these scoping semantics, a new kind of scope is introduced,
the :ref:`annotation scope <annotation-scopes>`. Annotation scopes behave for the
most part like function scopes, but interact differently with enclosing class scopes.
In Python 3.13, :term:`annotations <annotation>` will also be evaluated in
annotation scopes.

See :pep:`695` for more details.

(PEP written by Eric Traut. Implementation by Jelle Zijlstra, Eric Traut,
and others in :gh:`103764`.)

.. _whatsnew312-pep701:

PEP 701: Syntactic formalization of f-strings
---------------------------------------------

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

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

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

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

    >>> f"""{f'''{f'{f"{1+1}"}'}'''}"""
    '2'

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

    >>> f"{f"{f"{f"{f"{f"{1+1}"}"}"}"}"}"
    '2'

* Multi-line expressions and comments: In Python 3.11, f-string expressions
  must be defined in a single line, even if the expression within the f-string
  could normally span multiple lines
  (like literal lists being defined over multiple lines),
  making them harder to read. In Python 3.12 you can now define f-strings
  spanning multiple lines, and add inline comments:

    >>> f"This is the playlist: {", ".join([
    ...     'Take me back to Eden',  # My, my, those eyes like fire
    ...     'Alkaline',              # Not acid nor alkaline
    ...     'Ascensionism'           # Take to the broken skies at last
    ... ])}"
    'This is the playlist: Take me back to Eden, Alkaline, Ascensionism'

* Backslashes and unicode characters: before Python 3.12 f-string expressions
  couldn't contain any ``\`` character. This also affected unicode :ref:`escape
  sequences <escape-sequences>` (such as ``\N{snowman}``) as these contain
  the ``\N`` part that previously could not be part of expression components of
  f-strings. Now, you can define expressions like this:

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

See :pep:`701` for more details.

As a positive side-effect of how this feature has been implemented (by parsing f-strings
with :pep:`the PEG parser <617>`), now error messages for f-strings are more precise
and include the exact location of the error. For example, in Python 3.11, the following
f-string raises a :exc:`SyntaxError`:

.. code-block:: python

    >>> my_string = f"{x z y}" + f"{1 + 1}"
      File "<stdin>", line 1
        (x z y)
         ^^^
    SyntaxError: f-string: invalid syntax. Perhaps you forgot a comma?

but the error message doesn't include the exact location of the error within the line and
also has the expression artificially surrounded by parentheses. In Python 3.12, as f-strings
are parsed with the PEG parser, error messages can be more precise and show the entire line:

.. code-block:: python

    >>> my_string = f"{x z y}" + f"{1 + 1}"
      File "<stdin>", line 1
        my_string = f"{x z y}" + f"{1 + 1}"
                       ^^^
    SyntaxError: invalid syntax. Perhaps you forgot a comma?

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

.. _whatsnew312-pep684:

PEP 684: A Per-Interpreter GIL
------------------------------

:pep:`684` introduces a per-interpreter :term:`GIL <global interpreter lock>`,
so that sub-interpreters may now be created with a unique GIL per interpreter.
This allows Python programs to take full advantage of multiple CPU
cores. This is currently only available through the C-API,
though a Python API is :pep:`anticipated for 3.13 <554>`.

Use the new :c:func:`Py_NewInterpreterFromConfig` function to
create an interpreter with its own GIL:

.. code-block:: c

   PyInterpreterConfig config = {
       .check_multi_interp_extensions = 1,
       .gil = PyInterpreterConfig_OWN_GIL,
   };
   PyThreadState *tstate = NULL;
   PyStatus status = Py_NewInterpreterFromConfig(&tstate, &config);
   if (PyStatus_Exception(status)) {
       return -1;
   }
   /* The new interpreter is now active in the current thread. */

For further examples how to use the C-API for sub-interpreters with a
per-interpreter GIL, see :source:`Modules/_xxsubinterpretersmodule.c`.

(Contributed by Eric Snow in :gh:`104210`, etc.)

.. _whatsnew312-pep669:

PEP 669: Low impact monitoring for CPython
------------------------------------------

:pep:`669` defines a new :mod:`API <sys.monitoring>` for profilers,
debuggers, and other tools to monitor events in CPython.
It covers a wide range of events, including calls,
returns, lines, exceptions, jumps, and more.
This means that you only pay for what you use, providing support
for near-zero overhead debuggers and coverage tools.
See  :mod:`sys.monitoring` for details.

(Contributed by Mark Shannon in :gh:`103082`.)

.. _whatsnew312-pep688:

PEP 688: Making the buffer protocol accessible in Python
--------------------------------------------------------

:pep:`688` introduces a way to use the :ref:`buffer protocol <bufferobjects>`
from Python code. Classes that implement the :meth:`~object.__buffer__` method
are now usable as buffer types.

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

.. _whatsnew312-pep709:

PEP 709: Comprehension inlining
-------------------------------

Dictionary, list, and set comprehensions are now inlined, rather than creating a
new single-use function object for each execution of the comprehension. This
speeds up execution of a comprehension by up to two times.
See :pep:`709` for further details.

Comprehension iteration variables remain isolated and don't overwrite a
variable of the same name in the outer scope, nor are they visible after the
comprehension. Inlining does result in a few visible behavior changes:

* There is no longer a separate frame for the comprehension in tracebacks,
  and tracing/profiling no longer shows the comprehension as a function call.
* The :mod:`symtable` module will no longer produce child symbol tables for each
  comprehension; instead, the comprehension's locals will be included in the
  parent function's symbol table.
* Calling :func:`locals` inside a comprehension now includes variables
  from outside the comprehension, and no longer includes the synthetic ``.0``
  variable for the comprehension "argument".
* A comprehension iterating directly over ``locals()`` (e.g. ``[k for k in
  locals()]``) may see "RuntimeError: dictionary changed size during iteration"
  when run under tracing (e.g. code coverage measurement). This is the same
  behavior already seen in e.g. ``for k in locals():``. To avoid the error, first
  create a list of keys to iterate over: ``keys = list(locals()); [k for k in
  keys]``.

(Contributed by Carl Meyer and Vladimir Matveev in :pep:`709`.)

Improved Error Messages
-----------------------

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

    >>> sys.version_info
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    NameError: name 'sys' is not defined. Did you forget to import 'sys'?

* Improve the error suggestion for :exc:`NameError` exceptions for instances.
  Now if a :exc:`NameError` is raised in a method and the instance has an
  attribute that's exactly equal to the name in the exception, the suggestion
  will include ``self.<NAME>`` instead of the closest match in the method
  scope. (Contributed by Pablo Galindo in :gh:`99139`.)

    >>> class A:
    ...    def __init__(self):
    ...        self.blech = 1
    ...
    ...    def foo(self):
    ...        somethin = blech
    ...
    >>> A().foo()
    Traceback (most recent call last):
      File "<stdin>", line 1
        somethin = blech
                   ^^^^^
    NameError: name 'blech' is not defined. Did you mean: 'self.blech'?

* Improve the :exc:`SyntaxError` error message when the user types ``import x
  from y`` instead of ``from y import x``. (Contributed by Pablo Galindo in :gh:`98931`.)

    >>> import a.y.z from b.y.z
    Traceback (most recent call last):
      File "<stdin>", line 1
        import a.y.z from b.y.z
        ^^^^^^^^^^^^^^^^^^^^^^^
    SyntaxError: Did you mean to use 'from ... import ...' instead?

* :exc:`ImportError` exceptions raised from failed ``from <module> import
  <name>`` statements now include suggestions for the value of ``<name>`` based on the
  available names in ``<module>``. (Contributed by Pablo Galindo in :gh:`91058`.)

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


New Features Related to Type Hints
==================================

This section covers major changes affecting :pep:`type hints <484>` and
the :mod:`typing` module.

.. _whatsnew312-pep692:

PEP 692: Using ``TypedDict`` for more precise ``**kwargs`` typing
-----------------------------------------------------------------

Typing ``**kwargs`` in a function signature as introduced by :pep:`484` allowed
for valid annotations only in cases where all of the ``**kwargs`` were of the
same type.

:pep:`692` specifies a more precise way of typing ``**kwargs`` by relying on
typed dictionaries::

   from typing import TypedDict, Unpack

   class Movie(TypedDict):
     name: str
     year: int

   def foo(**kwargs: Unpack[Movie]): ...

See :pep:`692` for more details.

(Contributed by Franek Magiera in :gh:`103629`.)

.. _whatsnew312-pep698:

PEP 698: Override Decorator for Static Typing
---------------------------------------------

A new decorator :func:`typing.override` has been added to the :mod:`typing`
module. It indicates to type checkers that the method is intended to override
a method in a superclass. This allows type checkers to catch mistakes where
a method that is intended to override something in a base class
does not in fact do so.

Example::

   from typing import override

   class Base:
     def get_color(self) -> str:
       return "blue"

   class GoodChild(Base):
     @override  # ok: overrides Base.get_color
     def get_color(self) -> str:
       return "yellow"

   class BadChild(Base):
     @override  # type checker error: does not override Base.get_color
     def get_colour(self) -> str:
       return "red"

See :pep:`698` for more details.

(Contributed by Steven Troxler in :gh:`101561`.)

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

* The parser now raises :exc:`SyntaxError` when parsing source code containing
  null bytes. (Contributed by Pablo Galindo in :gh:`96670`.)

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

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

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

* Exceptions raised in a class or type's ``__set_name__`` method are no longer
  wrapped by a :exc:`RuntimeError`. Context information is added to the
  exception as a :pep:`678` note. (Contributed by Irit Katriel in :gh:`77757`.)

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

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

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

* :class:`memoryview` now supports the half-float type (the "e" format code).
  (Contributed by Donghee Na and Antoine Pitrou in :gh:`90751`.)

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

* :func:`sum` now uses Neumaier summation to improve accuracy and commutativity
  when summing floats or mixed ints and floats.
  (Contributed by Raymond Hettinger in :gh:`100425`.)

* :func:`ast.parse` now raises :exc:`SyntaxError` instead of :exc:`ValueError`
  when parsing source code containing null bytes. (Contributed by Pablo Galindo
  in :gh:`96670`.)

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

* :class:`types.MappingProxyType` instances are now hashable if the underlying
  mapping is hashable.
  (Contributed by Serhiy Storchaka in :gh:`87995`.)

* Add :ref:`support for the perf profiler <perf_profiling>` through the new
  environment variable :envvar:`PYTHONPERFSUPPORT`
  and command-line option :option:`-X perf <-X>`,
  as well as the new :func:`sys.activate_stack_trampoline`,
  :func:`sys.deactivate_stack_trampoline`,
  and :func:`sys.is_stack_trampoline_active` functions.
  (Design by Pablo Galindo. Contributed by Pablo Galindo and Christian Heimes
  with contributions from Gregory P. Smith [Google] and Mark Shannon
  in :gh:`96123`.)


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

* None.


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

array
-----

* The :class:`array.array` class now supports subscripting, making it a
  :term:`generic type`. (Contributed by Jelle Zijlstra in :gh:`98658`.)

asyncio
-------

* The performance of writing to sockets in :mod:`asyncio` has been
  significantly improved. ``asyncio`` now avoids unnecessary copying when
  writing to sockets and uses :meth:`~socket.socket.sendmsg` if the platform
  supports it. (Contributed by Kumar Aditya in :gh:`91166`.)

* Add :func:`asyncio.eager_task_factory` and :func:`asyncio.create_eager_task_factory`
  functions to allow opting an event loop in to eager task execution,
  making some use-cases 2x to 5x faster.
  (Contributed by Jacob Bower & Itamar Oren in :gh:`102853`, :gh:`104140`, and :gh:`104138`)

* On Linux, :mod:`asyncio` uses :class:`asyncio.PidfdChildWatcher` by default
  if :func:`os.pidfd_open` is available and functional instead of
  :class:`asyncio.ThreadedChildWatcher`.
  (Contributed by Kumar Aditya in :gh:`98024`.)

* The event loop now uses the best available child watcher for each platform
  (:class:`asyncio.PidfdChildWatcher` if supported and
  :class:`asyncio.ThreadedChildWatcher` otherwise), so manually
  configuring a child watcher is not recommended.
  (Contributed by Kumar Aditya in :gh:`94597`.)

* Add *loop_factory* parameter to :func:`asyncio.run` to allow specifying
  a custom event loop factory.
  (Contributed by Kumar Aditya in :gh:`99388`.)

* Add C implementation of :func:`asyncio.current_task` for 4x-6x speedup.
  (Contributed by Itamar Oren and Pranav Thulasiram Bhat in :gh:`100344`.)

* :func:`asyncio.iscoroutine` now returns ``False`` for generators as
  :mod:`asyncio` does not support legacy generator-based coroutines.
  (Contributed by Kumar Aditya in :gh:`102748`.)

* :func:`asyncio.wait` and :func:`asyncio.as_completed` now accepts generators
  yielding tasks.
  (Contributed by Kumar Aditya in :gh:`78530`.)

calendar
--------

* Add enums :data:`calendar.Month` and :data:`calendar.Day`
  defining months of the year and days of the week.
  (Contributed by Prince Roshan in :gh:`103636`.)

csv
---

* Add :const:`csv.QUOTE_NOTNULL` and :const:`csv.QUOTE_STRINGS` flags to
  provide finer grained control of ``None`` and empty strings by
  :class:`csv.writer` objects.

dis
---

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

* Add the :data:`dis.hasexc` collection to signify instructions that set
  an exception handler. (Contributed by Irit Katriel in :gh:`94216`.)

fractions
---------

* Objects of type :class:`fractions.Fraction` now support float-style
  formatting. (Contributed by Mark Dickinson in :gh:`100161`.)

importlib.resources
-------------------

* :func:`importlib.resources.as_file` now supports resource directories.
  (Contributed by Jason R. Coombs in :gh:`97930`.)

* Rename first parameter of :func:`importlib.resources.files` to *anchor*.
  (Contributed by Jason R. Coombs in :gh:`100598`.)

inspect
-------

* Add :func:`inspect.markcoroutinefunction` to mark sync functions that return
  a :term:`coroutine` for use with :func:`inspect.iscoroutinefunction`.
  (Contributed by Carlton Gibson in :gh:`99247`.)

* Add :func:`inspect.getasyncgenstate` and :func:`inspect.getasyncgenlocals`
  for determining the current state of asynchronous generators.
  (Contributed by Thomas Krennwallner in :gh:`79940`.)

* The performance of :func:`inspect.getattr_static` has been considerably
  improved. Most calls to the function should be at least 2x faster than they
  were in Python 3.11. (Contributed by Alex Waygood in :gh:`103193`.)

itertools
---------

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

math
----

* Add :func:`math.sumprod` for computing a sum of products.
  (Contributed by Raymond Hettinger in :gh:`100485`.)

* Extend :func:`math.nextafter` to include a *steps* argument
  for moving up or down multiple steps at a time. (Contributed by
  Matthias Goergens, Mark Dickinson, and Raymond Hettinger in :gh:`94906`.)

os
--

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

* :class:`os.DirEntry` now includes an :meth:`os.DirEntry.is_junction`
  method to check if the entry is a junction.
  (Contributed by Charles Machalow in :gh:`99547`.)

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

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

* As of 3.12.4, :func:`os.mkdir` and :func:`os.makedirs` on Windows
  now support passing a *mode* value of ``0o700`` to apply access
  control to the new directory. This implicitly affects
  :func:`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`.)

os.path
-------

* Add :func:`os.path.isjunction` to check if a given path is a junction.
  (Contributed by Charles Machalow in :gh:`99547`.)

* Add :func:`os.path.splitroot` to split a path into a triad
  ``(drive, root, tail)``. (Contributed by Barney Gale in :gh:`101000`.)

pathlib
-------

* Add support for subclassing :class:`pathlib.PurePath` and
  :class:`pathlib.Path`, plus their Posix- and Windows-specific variants.
  Subclasses may override the :meth:`pathlib.PurePath.with_segments` method
  to pass information between path instances.

* Add :meth:`pathlib.Path.walk` for walking the directory trees and generating
  all file or directory names within them, similar to :func:`os.walk`.
  (Contributed by Stanislav Zmiev in :gh:`90385`.)

* Add *walk_up* optional parameter to :meth:`pathlib.PurePath.relative_to`
  to allow the insertion of ``..`` entries in the result; this behavior is
  more consistent with :func:`os.path.relpath`.
  (Contributed by Domenico Ragusa in :gh:`84538`.)

* Add :meth:`pathlib.Path.is_junction` as a proxy to :func:`os.path.isjunction`.
  (Contributed by Charles Machalow in :gh:`99547`.)

* Add *case_sensitive* optional parameter to :meth:`pathlib.Path.glob`,
  :meth:`pathlib.Path.rglob` and :meth:`pathlib.PurePath.match` for matching
  the path's case sensitivity, allowing for more precise control over the matching process.

pdb
---

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

random
------

* Add :func:`random.binomialvariate`.
  (Contributed by Raymond Hettinger in :gh:`81620`.)

* Add a default of ``lambd=1.0`` to :func:`random.expovariate`.
  (Contributed by Raymond Hettinger in :gh:`100234`.)

shutil
------

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

* :func:`shutil.rmtree` now accepts a new argument *onexc* which is an
  error handler like *onerror* but which expects an exception instance
  rather than a *(typ, val, tb)* triplet. *onerror* is deprecated.
  (Contributed by Irit Katriel in :gh:`102828`.)

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

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

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

sqlite3
-------

* Add a :ref:`command-line interface <sqlite3-cli>`.
  (Contributed by Erlend E. Aasland in :gh:`77617`.)

* Add the :attr:`sqlite3.Connection.autocommit` attribute
  to :class:`sqlite3.Connection`
  and the *autocommit* parameter to :func:`sqlite3.connect`
  to control :pep:`249`-compliant
  :ref:`transaction handling <sqlite3-transaction-control-autocommit>`.
  (Contributed by Erlend E. Aasland in :gh:`83638`.)

* Add *entrypoint* keyword-only parameter to
  :meth:`sqlite3.Connection.load_extension`,
  for overriding the SQLite extension entry point.
  (Contributed by Erlend E. Aasland in :gh:`103015`.)

* Add :meth:`sqlite3.Connection.getconfig` and
  :meth:`sqlite3.Connection.setconfig` to :class:`sqlite3.Connection`
  to make configuration changes to a database connection.
  (Contributed by Erlend E. Aasland in :gh:`103489`.)

statistics
----------

* Extend :func:`statistics.correlation` to include as a ``ranked`` method
  for computing the Spearman correlation of ranked data.
  (Contributed by Raymond Hettinger in :gh:`95861`.)

sys
---

* Add the :mod:`sys.monitoring` namespace to expose the new :ref:`PEP 669
  <whatsnew312-pep669>` monitoring API.
  (Contributed by Mark Shannon in :gh:`103082`.)

* Add :func:`sys.activate_stack_trampoline` and
  :func:`sys.deactivate_stack_trampoline` for activating and deactivating
  stack profiler trampolines,
  and :func:`sys.is_stack_trampoline_active` for querying if stack profiler
  trampolines are active.
  (Contributed by Pablo Galindo and Christian Heimes
  with contributions from Gregory P. Smith [Google] and Mark Shannon
  in :gh:`96123`.)

* Add :data:`sys.last_exc` which holds the last unhandled exception that
  was raised (for post-mortem debugging use cases). Deprecate the
  three fields that have the same information in its legacy form:
  :data:`sys.last_type`, :data:`sys.last_value` and :data:`sys.last_traceback`.
  (Contributed by Irit Katriel in :gh:`102778`.)

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

* :func:`sys.setrecursionlimit` and :func:`sys.getrecursionlimit`.
  The recursion limit now applies only to Python code. Builtin functions do
  not use the recursion limit, but are protected by a different mechanism
  that prevents recursion from causing a virtual machine crash.

tempfile
--------

* The :class:`tempfile.NamedTemporaryFile` function has a new optional parameter
  *delete_on_close* (Contributed by Evgeny Zorin in :gh:`58451`.)
* :func:`tempfile.mkdtemp` now always returns an absolute path, even if the
  argument provided to the *dir* parameter is a relative path.
* As of 3.12.4 on Windows, the default mode ``0o700`` used by
  :func:`tempfile.mkdtemp` now limits access to the new directory due to
  changes to :func:`os.mkdir`. This is a mitigation for :cve:`2024-4030`.
  (Contributed by Steve Dower in :gh:`118486`.)

threading
---------

* Add :func:`threading.settrace_all_threads` and
  :func:`threading.setprofile_all_threads` that allow to set tracing and
  profiling functions in all running threads in addition to the calling one.
  (Contributed by Pablo Galindo in :gh:`93503`.)

tkinter
-------

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

tokenize
--------

* The :mod:`tokenize` module includes the changes introduced in :pep:`701`.
  (Contributed by Marta Gómez Macías and Pablo Galindo in :gh:`102856`.)
  See :ref:`whatsnew312-porting-to-python312` for more information on the
  changes to the :mod:`tokenize` module.

types
-----

* Add :func:`types.get_original_bases` to allow for further introspection of
  :ref:`user-defined-generics` when subclassed. (Contributed by
  James Hilton-Balfe and Alex Waygood in :gh:`101827`.)

.. _whatsnew-typing-py312:

typing
------

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

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

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

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

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

* All :data:`typing.TypedDict` and :data:`typing.NamedTuple` classes now have the
  ``__orig_bases__`` attribute. (Contributed by Adrian Garcia Badaracco in
  :gh:`103699`.)

* Add ``frozen_default`` parameter to :func:`typing.dataclass_transform`.
  (Contributed by Erik De Bonte in :gh:`99957`.)

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

* The Unicode database has been updated to version 15.0.0. (Contributed by
  Benjamin Peterson in :gh:`96734`).

unittest
--------

Add a ``--durations`` command line option, showing the N slowest test cases::

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

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

  OK (skipped=3)

(Contributed by Giampaolo Rodola in :gh:`48330`)

uuid
----

* Add a :ref:`command-line interface <uuid-cli>`.
  (Contributed by Adam Chhina in :gh:`88597`.)


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

* Remove ``wstr`` and ``wstr_length`` members from Unicode objects.
  It reduces object size by 8 or 16 bytes on 64bit platform. (:pep:`623`)
  (Contributed by Inada Naoki in :gh:`92536`.)

* Add experimental support for using the BOLT binary optimizer in the build
  process, which improves performance by 1-5%.
  (Contributed by Kevin Modzelewski in :gh:`90536` and tuned by Donghee Na in :gh:`101525`)

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

* Speed up :class:`asyncio.Task` creation by deferring expensive string formatting.
  (Contributed by Itamar Oren in :gh:`103793`.)

* The :func:`tokenize.tokenize` and :func:`tokenize.generate_tokens` functions are
  up to 64% faster as a side effect of the changes required to cover :pep:`701` in
  the :mod:`tokenize` module. (Contributed by Marta Gómez Macías and Pablo Galindo
  in :gh:`102856`.)

* Speed up :func:`super` method calls and attribute loads via the
  new :opcode:`LOAD_SUPER_ATTR` instruction. (Contributed by Carl Meyer and
  Vladimir Matveev in :gh:`103497`.)


CPython bytecode changes
========================

* Remove the :opcode:`!LOAD_METHOD` instruction. It has been merged into
  :opcode:`LOAD_ATTR`. :opcode:`LOAD_ATTR` will now behave like the old
  :opcode:`!LOAD_METHOD` instruction if the low bit of its oparg is set.
  (Contributed by Ken Jin in :gh:`93429`.)

* Remove the :opcode:`!JUMP_IF_FALSE_OR_POP` and :opcode:`!JUMP_IF_TRUE_OR_POP`
  instructions. (Contributed by Irit Katriel in :gh:`102859`.)

* Remove the :opcode:`!PRECALL` instruction. (Contributed by Mark Shannon in
  :gh:`92925`.)

* Add the :opcode:`BINARY_SLICE` and :opcode:`STORE_SLICE` instructions.
  (Contributed by Mark Shannon in :gh:`94163`.)

* Add the :opcode:`CALL_INTRINSIC_1` instructions.
  (Contributed by Mark Shannon in :gh:`99005`.)

* Add the :opcode:`CALL_INTRINSIC_2` instruction.
  (Contributed by Irit Katriel in :gh:`101799`.)

* Add the :opcode:`CLEANUP_THROW` instruction.
  (Contributed by Brandt Bucher in :gh:`90997`.)

* Add the :opcode:`!END_SEND` instruction.
  (Contributed by Mark Shannon in :gh:`103082`.)

* Add the :opcode:`LOAD_FAST_AND_CLEAR` instruction as part of the
  implementation of :pep:`709`. (Contributed by Carl Meyer in :gh:`101441`.)

* Add the :opcode:`LOAD_FAST_CHECK` instruction.
  (Contributed by Dennis Sweeney in :gh:`93143`.)

* Add the :opcode:`LOAD_FROM_DICT_OR_DEREF`, :opcode:`LOAD_FROM_DICT_OR_GLOBALS`,
  and :opcode:`LOAD_LOCALS` opcodes as part of the implementation of :pep:`695`.
  Remove the :opcode:`!LOAD_CLASSDEREF` opcode, which can be replaced with
  :opcode:`LOAD_LOCALS` plus :opcode:`LOAD_FROM_DICT_OR_DEREF`. (Contributed
  by Jelle Zijlstra in :gh:`103764`.)

* Add the :opcode:`LOAD_SUPER_ATTR` instruction. (Contributed by Carl Meyer and
  Vladimir Matveev in :gh:`103497`.)

* Add the :opcode:`RETURN_CONST` instruction. (Contributed by Wenyang Wang in :gh:`101632`.)

Demos and Tools
===============

* Remove the ``Tools/demo/`` directory which contained old demo scripts. A copy
  can be found in the `old-demos project
  <https://github.com/gvanrossum/old-demos>`_.
  (Contributed by Victor Stinner in :gh:`97681`.)

* Remove outdated example scripts of the ``Tools/scripts/`` directory.
  A copy can be found in the `old-demos project
  <https://github.com/gvanrossum/old-demos>`_.
  (Contributed by Victor Stinner in :gh:`97669`.)


Deprecated
==========

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

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

  * :class:`!ast.Num`
  * :class:`!ast.Str`
  * :class:`!ast.Bytes`
  * :class:`!ast.NameConstant`
  * :class:`!ast.Ellipsis`

  Use :class:`ast.Constant` instead.
  (Contributed by Serhiy Storchaka in :gh:`90953`.)

* :mod:`asyncio`:

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

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

  * The :meth:`~asyncio.get_event_loop` method of the
    default event loop policy now emits a :exc:`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`.)

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

* :mod:`collections.abc`: Deprecated :class:`collections.abc.ByteString`.
  Prefer :class:`Sequence` or :class:`collections.abc.Buffer`.
  For use in typing, prefer a union, like ``bytes | bytearray``, or :class:`collections.abc.Buffer`.
  (Contributed by Shantanu Jain in :gh:`91896`.)

* :mod:`datetime`: :class:`datetime.datetime`'s :meth:`~datetime.datetime.utcnow` and
  :meth:`~datetime.datetime.utcfromtimestamp` are deprecated and will be
  removed in a future version. Instead, use timezone-aware objects to represent
  datetimes in UTC: respectively, call :meth:`~datetime.datetime.now` and
  :meth:`~datetime.datetime.fromtimestamp`  with the *tz* parameter set to
  :const:`datetime.UTC`.
  (Contributed by Paul Ganssle in :gh:`103857`.)

* :mod:`email`: Deprecate the *isdst* parameter in :func:`email.utils.localtime`.
  (Contributed by Alan Williams in :gh:`72346`.)

* :mod:`importlib.abc`: Deprecated the following classes, scheduled for removal in
  Python 3.14:

  * :class:`!importlib.abc.ResourceReader`
  * :class:`!importlib.abc.Traversable`
  * :class:`!importlib.abc.TraversableResources`

  Use :mod:`importlib.resources.abc` classes instead:

  * :class:`importlib.resources.abc.Traversable`
  * :class:`importlib.resources.abc.TraversableResources`

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

* :mod:`itertools`: Deprecate the support for copy, deepcopy, and pickle operations,
  which is undocumented, inefficient, historically buggy, and inconsistent.
  This will be removed in 3.14 for a significant reduction in code
  volume and maintenance burden.
  (Contributed by Raymond Hettinger in :gh:`101588`.)

* :mod:`multiprocessing`: In Python 3.14, the default :mod:`multiprocessing`
  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
  :func:`~multiprocessing.get_context` or
  :func:`~multiprocessing.set_start_method` APIs to explicitly specify when
  your code *requires* ``'fork'``.  See :ref:`contexts and start methods
  <multiprocessing-start-methods>`.

* :mod:`pkgutil`: :func:`pkgutil.find_loader` and :func:`pkgutil.get_loader`
  are deprecated and will be removed in Python 3.14;
  use :func:`importlib.util.find_spec` instead.
  (Contributed by Nikita Sobolev in :gh:`97850`.)

* :mod:`pty`: The module has two undocumented ``master_open()`` and ``slave_open()``
  functions that have been deprecated since Python 2 but only gained a
  proper :exc:`DeprecationWarning` in 3.12. Remove them in 3.14.
  (Contributed by Soumendra Ganguly and Gregory P. Smith in :gh:`85984`.)

* :mod:`os`:

  * The ``st_ctime`` fields return by :func:`os.stat` and :func:`os.lstat` on
    Windows are deprecated. In a future release, they will contain the last
    metadata change time, consistent with other platforms. For now, they still
    contain the creation time, which is also available in the new ``st_birthtime``
    field. (Contributed by Steve Dower in :gh:`99726`.)

  * On POSIX platforms, :func:`os.fork` can now raise a
    :exc:`DeprecationWarning` when it can detect being called from a
    multithreaded process. There has always been a fundamental incompatibility
    with the POSIX platform when doing so. Even if such code *appeared* to work.
    We added the warning to raise awareness as issues encountered by code doing
    this are becoming more frequent. See the :func:`os.fork` documentation for
    more details along with `this discussion on fork being incompatible with threads
    <https://discuss.python.org/t/33555>`_ for *why* we're now surfacing this
    longstanding platform compatibility problem to developers.

  When this warning appears due to usage of :mod:`multiprocessing` or
  :mod:`concurrent.futures` the fix is to use a different
  :mod:`multiprocessing` start method such as ``"spawn"`` or ``"forkserver"``.

* :mod:`shutil`: The *onerror* argument of :func:`shutil.rmtree` is deprecated;
  use *onexc* instead. (Contributed by Irit Katriel in :gh:`102828`.)

* :mod:`sqlite3`:

  * :ref:`default adapters and converters
    <sqlite3-default-converters>` are now deprecated.
    Instead, use the :ref:`sqlite3-adapter-converter-recipes`
    and tailor them to your needs.
    (Contributed by Erlend E. Aasland in :gh:`90016`.)

  * In :meth:`~sqlite3.Cursor.execute`, :exc:`DeprecationWarning` is now emitted
    when :ref:`named placeholders <sqlite3-placeholders>` are used together with
    parameters supplied as a :term:`sequence` instead of as a :class:`dict`.
    Starting from Python 3.14, using named placeholders with parameters supplied
    as a sequence will raise a :exc:`~sqlite3.ProgrammingError`.
    (Contributed by Erlend E. Aasland in :gh:`101698`.)

* :mod:`sys`: The :data:`sys.last_type`, :data:`sys.last_value` and :data:`sys.last_traceback`
  fields are deprecated. Use :data:`sys.last_exc` instead.
  (Contributed by Irit Katriel in :gh:`102778`.)

* :mod:`tarfile`: Extracting tar archives without specifying *filter* is deprecated until
  Python 3.14, when ``'data'`` filter will become the default.
  See :ref:`tarfile-extraction-filter` for details.

* :mod:`typing`:

  * :class:`typing.Hashable` and :class:`typing.Sized`, aliases for
    :class:`collections.abc.Hashable` and :class:`collections.abc.Sized` respectively, are
    deprecated. (:gh:`94309`.)

  * :class:`typing.ByteString`, deprecated since Python 3.9, now causes a
    :exc:`DeprecationWarning` to be emitted when it is used.
    (Contributed by Alex Waygood in :gh:`91896`.)

* :mod:`xml.etree.ElementTree`: The module now emits :exc:`DeprecationWarning`
  when testing the truth value of an :class:`xml.etree.ElementTree.Element`.
  Before, the Python implementation emitted :exc:`FutureWarning`, and the C
  implementation emitted nothing.
  (Contributed by Jacob Walls in :gh:`83122`.)

* The 3-arg signatures (type, value, traceback) of :meth:`coroutine throw()
  <coroutine.throw>`, :meth:`generator throw() <generator.throw>` and
  :meth:`async generator throw() <agen.athrow>` are deprecated and
  may be removed in a future version of Python. Use the single-arg versions
  of these functions instead. (Contributed by Ofey Chan in :gh:`89874`.)

* :exc:`DeprecationWarning` is now raised when ``__package__`` on a
  module differs from ``__spec__.parent`` (previously it was
  :exc:`ImportWarning`).
  (Contributed by Brett Cannon in :gh:`65961`.)

* Setting ``__package__`` or ``__cached__`` on a module is deprecated,
  and will cease to be set or taken into consideration by the import system in Python 3.14.
  (Contributed by Brett Cannon in :gh:`65961`.)

* The bitwise inversion operator (``~``) on bool is deprecated. It will throw an
  error in Python 3.16. Use ``not`` for logical negation of bools instead.
  In the rare case that you really need the bitwise inversion of the underlying
  ``int``, convert to int explicitly: ``~int(x)``. (Contributed by Tim Hoffmann
  in :gh:`103487`.)

* Accessing :attr:`~codeobject.co_lnotab` on code objects was deprecated in
  Python 3.10 via :pep:`626`,
  but it only got a proper :exc:`DeprecationWarning` in 3.12,
  therefore it will be removed in 3.14.
  (Contributed by Nikita Sobolev in :gh:`101866`.)

.. include:: ../deprecations/pending-removal-in-3.13.rst

.. include:: ../deprecations/pending-removal-in-3.14.rst

.. include:: ../deprecations/pending-removal-in-3.15.rst

.. include:: ../deprecations/pending-removal-in-3.16.rst

.. include:: ../deprecations/pending-removal-in-future.rst

Removed
=======

asynchat and asyncore
---------------------

* These two modules have been removed
  according to the schedule in :pep:`594`,
  having been deprecated in Python 3.6.
  Use :mod:`asyncio` instead.
  (Contributed by Nikita Sobolev in :gh:`96580`.)

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

* Several names deprecated in the :mod:`configparser` way back in 3.2 have
  been removed per :gh:`89336`:

  * :class:`configparser.ParsingError` no longer has a ``filename`` attribute
    or argument. Use the ``source`` attribute and argument instead.
  * :mod:`configparser` no longer has a ``SafeConfigParser`` class. Use the
    shorter :class:`~configparser.ConfigParser` name instead.
  * :class:`configparser.ConfigParser` no longer has a ``readfp`` method.
    Use :meth:`~configparser.ConfigParser.read_file` instead.

distutils
---------

* Remove the :py:mod:`!distutils` package. It was deprecated in Python 3.10 by
  :pep:`632` "Deprecate distutils module". For projects still using
  ``distutils`` and cannot be updated to something else, the ``setuptools``
  project can be installed: it still provides ``distutils``.
  (Contributed by Victor Stinner in :gh:`92584`.)

ensurepip
---------

* Remove the bundled setuptools wheel from :mod:`ensurepip`,
  and stop installing setuptools in environments created by :mod:`venv`.

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

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

  (Contributed by Pradyun Gedam in :gh:`95299`.)

enum
----

* Remove :mod:`enum`'s ``EnumMeta.__getattr__``, which is no longer needed for
  enum attribute access.
  (Contributed by Ethan Furman in :gh:`95083`.)

ftplib
------

* Remove :mod:`ftplib`'s ``FTP_TLS.ssl_version`` class attribute: use the
  *context* parameter instead.
  (Contributed by Victor Stinner in :gh:`94172`.)

gzip
----

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

hashlib
-------

* Remove the pure Python implementation of :mod:`hashlib`'s
  :func:`hashlib.pbkdf2_hmac`, deprecated in Python 3.10. Python 3.10 and
  newer requires OpenSSL 1.1.1 (:pep:`644`): this OpenSSL version provides
  a C implementation of :func:`~hashlib.pbkdf2_hmac` which is faster.
  (Contributed by Victor Stinner in :gh:`94199`.)

importlib
---------

* Many previously deprecated cleanups in :mod:`importlib` have now been
  completed:

  * References to, and support for :meth:`!module_repr` has been removed.
    (Contributed by Barry Warsaw in :gh:`97850`.)

  * ``importlib.util.set_package``, ``importlib.util.set_loader`` and
    ``importlib.util.module_for_loader`` have all been removed. (Contributed by
    Brett Cannon and Nikita Sobolev in :gh:`65961` and :gh:`97850`.)

  * Support for ``find_loader()`` and ``find_module()`` APIs have been
    removed.  (Contributed by Barry Warsaw in :gh:`98040`.)

  * ``importlib.abc.Finder``, ``pkgutil.ImpImporter``, and ``pkgutil.ImpLoader``
    have been removed.  (Contributed by Barry Warsaw in :gh:`98040`.)

imp
---

* The :mod:`!imp` module has been removed.  (Contributed by Barry Warsaw in
  :gh:`98040`.)

  To migrate, consult the following correspondence table:

    =================================  =======================================
       imp                                importlib
    =================================  =======================================
    ``imp.NullImporter``               Insert ``None`` into ``sys.path_importer_cache``
    ``imp.cache_from_source()``        :func:`importlib.util.cache_from_source`
    ``imp.find_module()``              :func:`importlib.util.find_spec`
    ``imp.get_magic()``                :attr:`importlib.util.MAGIC_NUMBER`
    ``imp.get_suffixes()``             :attr:`importlib.machinery.SOURCE_SUFFIXES`, :attr:`importlib.machinery.EXTENSION_SUFFIXES`, and :attr:`importlib.machinery.BYTECODE_SUFFIXES`
    ``imp.get_tag()``                  :attr:`sys.implementation.cache_tag <sys.implementation>`
    ``imp.load_module()``              :func:`importlib.import_module`
    ``imp.new_module(name)``           ``types.ModuleType(name)``
    ``imp.reload()``                   :func:`importlib.reload`
    ``imp.source_from_cache()``        :func:`importlib.util.source_from_cache`
    ``imp.load_source()``              *See below*
    =================================  =======================================

  Replace ``imp.load_source()`` with::

        import importlib.util
        import importlib.machinery

        def load_source(modname, filename):
            loader = importlib.machinery.SourceFileLoader(modname, filename)
            spec = importlib.util.spec_from_file_location(modname, filename, loader=loader)
            module = importlib.util.module_from_spec(spec)
            # The module is always executed and not cached in sys.modules.
            # Uncomment the following line to cache the module.
            # sys.modules[module.__name__] = module
            loader.exec_module(module)
            return module

* Remove :mod:`!imp` functions and attributes with no replacements:

  * Undocumented functions:

    * ``imp.init_builtin()``
    * ``imp.load_compiled()``
    * ``imp.load_dynamic()``
    * ``imp.load_package()``

  * ``imp.lock_held()``, ``imp.acquire_lock()``, ``imp.release_lock()``:
    the locking scheme has changed in Python 3.3 to per-module locks.
  * ``imp.find_module()`` constants: ``SEARCH_ERROR``, ``PY_SOURCE``,
    ``PY_COMPILED``, ``C_EXTENSION``, ``PY_RESOURCE``, ``PKG_DIRECTORY``,
    ``C_BUILTIN``, ``PY_FROZEN``, ``PY_CODERESOURCE``, ``IMP_HOOK``.

io
--

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

locale
------

* Remove :mod:`locale`'s :func:`!locale.format` function, deprecated in Python 3.7:
  use :func:`locale.format_string` instead.
  (Contributed by Victor Stinner in :gh:`94226`.)

smtpd
-----

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

sqlite3
-------

* The following undocumented :mod:`sqlite3` features, deprecated in Python
  3.10, are now removed:

  * ``sqlite3.enable_shared_cache()``
  * ``sqlite3.OptimizedUnicode``

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

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

  (Contributed by Erlend E. Aasland in :gh:`92548`.)

ssl
---

* Remove :mod:`ssl`'s :func:`!ssl.RAND_pseudo_bytes` function, deprecated in Python 3.6:
  use :func:`os.urandom` or :func:`ssl.RAND_bytes` instead.
  (Contributed by Victor Stinner in :gh:`94199`.)

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

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

unittest
--------

* Remove many long-deprecated :mod:`unittest` features:

  .. _unittest-TestCase-removed-aliases:

  * A number of :class:`~unittest.TestCase` method aliases:

    ============================ =============================== ===============
       Deprecated alias           Method Name                     Deprecated in
    ============================ =============================== ===============
     ``failUnless``               :meth:`.assertTrue`             3.1
     ``failIf``                   :meth:`.assertFalse`            3.1
     ``failUnlessEqual``          :meth:`.assertEqual`            3.1
     ``failIfEqual``              :meth:`.assertNotEqual`         3.1
     ``failUnlessAlmostEqual``    :meth:`.assertAlmostEqual`      3.1
     ``failIfAlmostEqual``        :meth:`.assertNotAlmostEqual`   3.1
     ``failUnlessRaises``         :meth:`.assertRaises`           3.1
     ``assert_``                  :meth:`.assertTrue`             3.2
     ``assertEquals``             :meth:`.assertEqual`            3.2
     ``assertNotEquals``          :meth:`.assertNotEqual`         3.2
     ``assertAlmostEquals``       :meth:`.assertAlmostEqual`      3.2
     ``assertNotAlmostEquals``    :meth:`.assertNotAlmostEqual`   3.2
     ``assertRegexpMatches``      :meth:`.assertRegex`            3.2
     ``assertRaisesRegexp``       :meth:`.assertRaisesRegex`      3.2
     ``assertNotRegexpMatches``   :meth:`.assertNotRegex`         3.5
    ============================ =============================== ===============

    You can use https://github.com/isidentical/teyit to automatically modernise
    your unit tests.

  * Undocumented and broken :class:`~unittest.TestCase` method
    ``assertDictContainsSubset`` (deprecated in Python 3.2).

  * Undocumented :meth:`TestLoader.loadTestsFromModule
    <unittest.TestLoader.loadTestsFromModule>` parameter *use_load_tests*
    (deprecated and ignored since Python 3.5).

  * An alias of the :class:`~unittest.TextTestResult` class:
    ``_TextTestResult`` (deprecated in Python 3.2).

  (Contributed by Serhiy Storchaka in :gh:`89325`.)

webbrowser
----------

* Remove support for obsolete browsers from :mod:`webbrowser`.
  The removed browsers include: Grail, Mosaic, Netscape, Galeon, Skipstone,
  Iceape, Firebird, and Firefox versions 35 and below (:gh:`102871`).

xml.etree.ElementTree
---------------------

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

zipimport
---------

* Remove :mod:`zipimport`'s ``find_loader()`` and ``find_module()`` methods,
  deprecated in Python 3.10: use the ``find_spec()`` method instead.  See
  :pep:`451` for the rationale.
  (Contributed by Victor Stinner in :gh:`94379`.)

Others
------

* Remove the ``suspicious`` rule from the documentation :file:`Makefile` and
  :file:`Doc/tools/rstlint.py`, both in favor of `sphinx-lint
  <https://github.com/sphinx-contrib/sphinx-lint>`_.
  (Contributed by Julien Palard in :gh:`98179`.)

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

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

* Remove ``_use_broken_old_ctypes_structure_semantics_`` flag
  from :mod:`ctypes` module.
  (Contributed by Nikita Sobolev in :gh:`99285`.)


.. _whatsnew312-porting-to-python312:

Porting to Python 3.12
======================

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

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

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

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

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

* Remove the ``asyncore``-based ``smtpd`` module deprecated in Python 3.4.7
  and 3.5.4.  A recommended replacement is the
  :mod:`asyncio`-based :pypi:`aiosmtpd` PyPI module.

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

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

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

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

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

* When extracting tar files using :mod:`tarfile` or
  :func:`shutil.unpack_archive`, pass the *filter* argument to limit features
  that may be surprising or dangerous.
  See :ref:`tarfile-extraction-filter` for details.

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

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

  while the new version emits::

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

  Additionally, there may be some minor behavioral changes as a consequence of the
  changes required to support :pep:`701`. Some of these changes include:

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

  * Incomplete single-line strings now also raise :exc:`tokenize.TokenError` as incomplete
    multiline strings do.

  * Some incomplete or invalid Python code now raises :exc:`tokenize.TokenError` instead of
    returning arbitrary ``ERRORTOKEN`` tokens when tokenizing it.

  * Mixing tabs and spaces as indentation in the same file is not supported anymore and will
    raise a :exc:`TabError`.

* The :mod:`threading` module now expects the :mod:`!_thread` module to have
  an ``_is_main_interpreter`` attribute.  It is a function with no
  arguments that returns ``True`` if the current interpreter is the
  main interpreter.

  Any library or application that provides a custom ``_thread`` module
  should provide ``_is_main_interpreter()``.
  (See :gh:`112826`.)

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

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

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

* CPython now uses the ThinLTO option as the default link time optimization policy
  if the Clang compiler accepts the flag.
  (Contributed by Donghee Na in :gh:`89536`.)

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

* Add platform triplets for 64-bit LoongArch:

  * loongarch64-linux-gnusf
  * loongarch64-linux-gnuf32
  * loongarch64-linux-gnu

  (Contributed by Zhang Na in :gh:`90656`.)

* ``PYTHON_FOR_REGEN`` now require Python 3.10 or newer.

* Autoconf 2.71 and aclocal 1.16.4 is now required to regenerate
  :file:`!configure`.
  (Contributed by Christian Heimes in :gh:`89886`.)

* Windows builds and macOS installers from python.org now use OpenSSL 3.0.


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

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

.. _whatsnew312-pep697:

* :pep:`697`: Introduce the :ref:`Unstable C API tier <unstable-c-api>`,
  intended for low-level tools like debuggers and JIT compilers.
  This API may change in each minor release of CPython without deprecation
  warnings.
  Its contents are marked by the ``PyUnstable_`` prefix in names.

  Code object constructors:

  - ``PyUnstable_Code_New()`` (renamed from ``PyCode_New``)
  - ``PyUnstable_Code_NewWithPosOnlyArgs()`` (renamed from ``PyCode_NewWithPosOnlyArgs``)

  Extra storage for code objects (:pep:`523`):

  - ``PyUnstable_Eval_RequestCodeExtraIndex()`` (renamed from ``_PyEval_RequestCodeExtraIndex``)
  - ``PyUnstable_Code_GetExtra()`` (renamed from ``_PyCode_GetExtra``)
  - ``PyUnstable_Code_SetExtra()`` (renamed from ``_PyCode_SetExtra``)

  The original names will continue to be available until the respective
  API changes.

  (Contributed by Petr Viktorin in :gh:`101101`.)

* :pep:`697`: Add an API for extending types whose instance memory layout is
  opaque:

  - :c:member:`PyType_Spec.basicsize` can be zero or negative to specify
    inheriting or extending the base class size.
  - :c:func:`PyObject_GetTypeData` and :c:func:`PyType_GetTypeDataSize`
    added to allow access to subclass-specific instance data.
  - :c:macro:`Py_TPFLAGS_ITEMS_AT_END` and :c:func:`PyObject_GetItemData`
    added to allow safely extending certain variable-sized types, including
    :c:var:`PyType_Type`.
  - :c:macro:`Py_RELATIVE_OFFSET` added to allow defining
    :c:type:`members <PyMemberDef>` in terms of a subclass-specific struct.

  (Contributed by Petr Viktorin in :gh:`103509`.)

* Add the new :ref:`limited C API <limited-c-api>` function :c:func:`PyType_FromMetaclass`,
  which generalizes the existing :c:func:`PyType_FromModuleAndSpec` using
  an additional metaclass argument.
  (Contributed by Wenzel Jakob in :gh:`93012`.)

* API for creating objects that can be called using
  :ref:`the vectorcall protocol <vectorcall>` was added to the
  :ref:`Limited API <stable>`:

  * :c:macro:`Py_TPFLAGS_HAVE_VECTORCALL`
  * :c:func:`PyVectorcall_NARGS`
  * :c:func:`PyVectorcall_Call`
  * :c:type:`vectorcallfunc`

  The :c:macro:`Py_TPFLAGS_HAVE_VECTORCALL` flag is now removed from a class
  when the class's :py:meth:`~object.__call__` method is reassigned.
  This makes vectorcall safe to use with mutable types (i.e. heap types
  without the immutable flag, :c:macro:`Py_TPFLAGS_IMMUTABLETYPE`).
  Mutable types that do not override :c:member:`~PyTypeObject.tp_call` now
  inherit the ``Py_TPFLAGS_HAVE_VECTORCALL`` flag.
  (Contributed by Petr Viktorin in :gh:`93274`.)

  The :c:macro:`Py_TPFLAGS_MANAGED_DICT` and :c:macro:`Py_TPFLAGS_MANAGED_WEAKREF`
  flags have been added. This allows extensions classes to support object
  ``__dict__`` and weakrefs with less bookkeeping,
  using less memory and with faster access.

* API for performing calls using
  :ref:`the vectorcall protocol <vectorcall>` was added to the
  :ref:`Limited API <stable>`:

  * :c:func:`PyObject_Vectorcall`
  * :c:func:`PyObject_VectorcallMethod`
  * :c:macro:`PY_VECTORCALL_ARGUMENTS_OFFSET`

  This means that both the incoming and outgoing ends of the vector call
  protocol are now available in the :ref:`Limited API <stable>`. (Contributed
  by Wenzel Jakob in :gh:`98586`.)

* Add two new public functions,
  :c:func:`PyEval_SetProfileAllThreads` and
  :c:func:`PyEval_SetTraceAllThreads`, that allow to set tracing and profiling
  functions in all running threads in addition to the calling one. (Contributed
  by Pablo Galindo in :gh:`93503`.)

* Add new function :c:func:`PyFunction_SetVectorcall` to the C API
  which sets the vectorcall field of a given :c:type:`PyFunctionObject`.
  (Contributed by Andrew Frost in :gh:`92257`.)

* The C API now permits registering callbacks via :c:func:`PyDict_AddWatcher`,
  :c:func:`PyDict_Watch` and related APIs to be called whenever a dictionary
  is modified. This is intended for use by optimizing interpreters, JIT
  compilers, or debuggers.
  (Contributed by Carl Meyer in :gh:`91052`.)

* Add :c:func:`PyType_AddWatcher` and :c:func:`PyType_Watch` API to register
  callbacks to receive notification on changes to a type.
  (Contributed by Carl Meyer in :gh:`91051`.)

* Add :c:func:`PyCode_AddWatcher` and :c:func:`PyCode_ClearWatcher`
  APIs to register callbacks to receive notification on creation and
  destruction of code objects.
  (Contributed by Itamar Oren in :gh:`91054`.)

* Add :c:func:`PyFrame_GetVar` and :c:func:`PyFrame_GetVarString` functions to
  get a frame variable by its name.
  (Contributed by Victor Stinner in :gh:`91248`.)

* Add :c:func:`PyErr_GetRaisedException` and :c:func:`PyErr_SetRaisedException`
  for saving and restoring the current exception.
  These functions return and accept a single exception object,
  rather than the triple arguments of the now-deprecated
  :c:func:`PyErr_Fetch` and :c:func:`PyErr_Restore`.
  This is less error prone and a bit more efficient.
  (Contributed by Mark Shannon in :gh:`101578`.)

* Add ``_PyErr_ChainExceptions1``, which takes an exception instance,
  to replace the legacy-API ``_PyErr_ChainExceptions``, which is now
  deprecated. (Contributed by Mark Shannon in :gh:`101578`.)

* Add :c:func:`PyException_GetArgs` and :c:func:`PyException_SetArgs`
  as convenience functions for retrieving and modifying
  the :attr:`~BaseException.args` passed to the exception's constructor.
  (Contributed by Mark Shannon in :gh:`101578`.)

* Add :c:func:`PyErr_DisplayException`, which takes an exception instance,
  to replace the legacy-api :c:func:`!PyErr_Display`. (Contributed by
  Irit Katriel in :gh:`102755`).

.. _whatsnew312-pep683:

* :pep:`683`: Introduce *Immortal Objects*, which allows objects
  to bypass reference counts, and related changes to the C-API:

  - ``_Py_IMMORTAL_REFCNT``: The reference count that defines an object
      as immortal.
  - ``_Py_IsImmortal`` Checks if an object has the immortal reference count.
  - ``PyObject_HEAD_INIT`` This will now initialize reference count to
      ``_Py_IMMORTAL_REFCNT`` when used with ``Py_BUILD_CORE``.
  - ``SSTATE_INTERNED_IMMORTAL`` An identifier for interned unicode objects
       that are immortal.
  - ``SSTATE_INTERNED_IMMORTAL_STATIC`` An identifier for interned unicode
       objects that are immortal and static
  - ``sys.getunicodeinternedsize`` This returns the total number of unicode
      objects that have been interned. This is now needed for :file:`refleak.py` to
      correctly track reference counts and allocated blocks

  (Contributed by Eddie Elizondo in :gh:`84436`.)

* :pep:`684`: Add the new :c:func:`Py_NewInterpreterFromConfig`
  function and :c:type:`PyInterpreterConfig`, which may be used
  to create sub-interpreters with their own GILs.
  (See :ref:`whatsnew312-pep684` for more info.)
  (Contributed by Eric Snow in :gh:`104110`.)

* In the limited C API version 3.12, :c:func:`Py_INCREF` and
  :c:func:`Py_DECREF` functions are now implemented as opaque function calls to
  hide implementation details.
  (Contributed by Victor Stinner in :gh:`105387`.)

Porting to Python 3.12
----------------------

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

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

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

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

  To get a list of subclasses, call the Python method
  :py:meth:`~class.__subclasses__` (using :c:func:`PyObject_CallMethod`,
  for example).

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

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

* Fix wrong sign placement in :c:func:`PyUnicode_FromFormat` and
  :c:func:`PyUnicode_FromFormatV`.
  (Contributed by Philip Georgi in :gh:`95504`.)

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

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

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

* The interpreter's error indicator is now always normalized. This means
  that :c:func:`PyErr_SetObject`, :c:func:`PyErr_SetString` and the other
  functions that set the error indicator now normalize the exception
  before storing it. (Contributed by Mark Shannon in :gh:`101578`.)

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

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

  * :c:func:`PyType_FromSpec`
  * :c:func:`PyType_FromSpecWithBases`
  * :c:func:`PyType_FromModuleAndSpec`

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

  Note that :c:func:`PyType_FromMetaclass` (added in Python 3.12)
  already disallows creating classes whose metaclass overrides ``tp_new``
  (:meth:`~object.__new__` in Python).

  Since ``tp_new`` overrides almost everything ``PyType_From*`` functions do,
  the two are incompatible with each other.
  The existing behavior -- ignoring the metaclass for several steps
  of type creation -- is unsafe in general, since (meta)classes assume that
  ``tp_new`` was called.
  There is no simple general workaround. One of the following may work for you:

  - If you control the metaclass, avoid using ``tp_new`` in it:

    - If initialization can be skipped, it can be done in
      :c:member:`~PyTypeObject.tp_init` instead.
    - If the metaclass doesn't need to be instantiated from Python,
      set its ``tp_new`` to ``NULL`` using
      the :c:macro:`Py_TPFLAGS_DISALLOW_INSTANTIATION` flag.
      This makes it acceptable for ``PyType_From*`` functions.

  - Avoid ``PyType_From*`` functions: if you don't need C-specific features
    (slots or setting the instance size), create types by :ref:`calling <call>`
    the metaclass.

  - If you *know* the ``tp_new`` can be skipped safely, filter the deprecation
    warning out using :func:`warnings.catch_warnings` from Python.

* :c:var:`PyOS_InputHook` and :c:var:`PyOS_ReadlineFunctionPointer` are no
  longer called in :ref:`subinterpreters <sub-interpreter-support>`. This is
  because clients generally rely on process-wide global state (since these
  callbacks have no way of recovering extension module state).

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

* :c:struct:`PyLongObject` has had its internals changed for better performance.
  Although the internals of :c:struct:`PyLongObject` are private, they are used
  by some extension modules.
  The internal fields should no longer be accessed directly, instead the API
  functions beginning ``PyLong_...`` should be used instead.
  Two new *unstable* API functions are provided for efficient access to the
  value of :c:struct:`PyLongObject`\s which fit into a single machine word:

  * :c:func:`PyUnstable_Long_IsCompact`
  * :c:func:`PyUnstable_Long_CompactValue`

* Custom allocators, set via :c:func:`PyMem_SetAllocator`, are now
  required to be thread-safe, regardless of memory domain.  Allocators
  that don't have their own state, including "hooks", are not affected.
  If your custom allocator is not already thread-safe and you need
  guidance then please create a new GitHub issue
  and CC ``@ericsnowcurrently``.

Deprecated
----------

* In accordance with :pep:`699`, the ``ma_version_tag`` field in :c:type:`PyDictObject`
  is deprecated for extension modules. Accessing this field will generate a compiler
  warning at compile time. This field will be removed in Python 3.14.
  (Contributed by Ramvikrams and Kumar Aditya in :gh:`101193`. PEP by Ken Jin.)

* Deprecate global configuration variable:

  * :c:var:`Py_DebugFlag`: use :c:member:`PyConfig.parser_debug`
  * :c:var:`Py_VerboseFlag`: use :c:member:`PyConfig.verbose`
  * :c:var:`Py_QuietFlag`: use :c:member:`PyConfig.quiet`
  * :c:var:`Py_InteractiveFlag`: use :c:member:`PyConfig.interactive`
  * :c:var:`Py_InspectFlag`: use :c:member:`PyConfig.inspect`
  * :c:var:`Py_OptimizeFlag`: use :c:member:`PyConfig.optimization_level`
  * :c:var:`Py_NoSiteFlag`: use :c:member:`PyConfig.site_import`
  * :c:var:`Py_BytesWarningFlag`: use :c:member:`PyConfig.bytes_warning`
  * :c:var:`Py_FrozenFlag`: use :c:member:`PyConfig.pathconfig_warnings`
  * :c:var:`Py_IgnoreEnvironmentFlag`: use :c:member:`PyConfig.use_environment`
  * :c:var:`Py_DontWriteBytecodeFlag`: use :c:member:`PyConfig.write_bytecode`
  * :c:var:`Py_NoUserSiteDirectory`: use :c:member:`PyConfig.user_site_directory`
  * :c:var:`Py_UnbufferedStdioFlag`: use :c:member:`PyConfig.buffered_stdio`
  * :c:var:`Py_HashRandomizationFlag`: use :c:member:`PyConfig.use_hash_seed`
    and :c:member:`PyConfig.hash_seed`
  * :c:var:`Py_IsolatedFlag`: use :c:member:`PyConfig.isolated`
  * :c:var:`Py_LegacyWindowsFSEncodingFlag`: use :c:member:`PyPreConfig.legacy_windows_fs_encoding`
  * :c:var:`Py_LegacyWindowsStdioFlag`: use :c:member:`PyConfig.legacy_windows_stdio`
  * :c:var:`!Py_FileSystemDefaultEncoding`: use :c:member:`PyConfig.filesystem_encoding`
  * :c:var:`!Py_HasFileSystemDefaultEncoding`: use :c:member:`PyConfig.filesystem_encoding`
  * :c:var:`!Py_FileSystemDefaultEncodeErrors`: use :c:member:`PyConfig.filesystem_errors`
  * :c:var:`!Py_UTF8Mode`: use :c:member:`PyPreConfig.utf8_mode` (see :c:func:`Py_PreInitialize`)

  The :c:func:`Py_InitializeFromConfig` API should be used with
  :c:type:`PyConfig` instead.
  (Contributed by Victor Stinner in :gh:`77782`.)

* Creating :c:data:`immutable types <Py_TPFLAGS_IMMUTABLETYPE>` with mutable
  bases is deprecated and will be disabled in Python 3.14. (:gh:`95388`)

* The :file:`structmember.h` header is deprecated, though it continues to be
  available and there are no plans to remove it.

  Its contents are now available just by including :file:`Python.h`,
  with a ``Py`` prefix added if it was missing:

  - :c:struct:`PyMemberDef`, :c:func:`PyMember_GetOne` and
    :c:func:`PyMember_SetOne`
  - Type macros like :c:macro:`Py_T_INT`, :c:macro:`Py_T_DOUBLE`, etc.
    (previously ``T_INT``, ``T_DOUBLE``, etc.)
  - The flags :c:macro:`Py_READONLY` (previously ``READONLY``) and
    :c:macro:`Py_AUDIT_READ` (previously all uppercase)

  Several items are not exposed from :file:`Python.h`:

  - :c:macro:`T_OBJECT` (use :c:macro:`Py_T_OBJECT_EX`)
  - :c:macro:`T_NONE` (previously undocumented, and pretty quirky)
  - The macro ``WRITE_RESTRICTED`` which does nothing.
  - The macros ``RESTRICTED`` and ``READ_RESTRICTED``, equivalents of
    :c:macro:`Py_AUDIT_READ`.
  - In some configurations, ``<stddef.h>`` is not included from :file:`Python.h`.
    It should be included manually when using ``offsetof()``.

  The deprecated header continues to provide its original
  contents under the original names.
  Your old code can stay unchanged, unless the extra include and non-namespaced
  macros bother you greatly.

  (Contributed in :gh:`47146` by Petr Viktorin, based on
  earlier work by Alexander Belopolsky and Matthias Braun.)

* :c:func:`PyErr_Fetch` and :c:func:`PyErr_Restore` are deprecated.
  Use :c:func:`PyErr_GetRaisedException` and
  :c:func:`PyErr_SetRaisedException` instead.
  (Contributed by Mark Shannon in :gh:`101578`.)

* :c:func:`!PyErr_Display` is deprecated. Use :c:func:`PyErr_DisplayException`
  instead. (Contributed by Irit Katriel in :gh:`102755`).

* ``_PyErr_ChainExceptions`` is deprecated. Use ``_PyErr_ChainExceptions1``
  instead. (Contributed by Irit Katriel in :gh:`102192`.)

* Using :c:func:`PyType_FromSpec`, :c:func:`PyType_FromSpecWithBases`
  or :c:func:`PyType_FromModuleAndSpec` to create a class whose metaclass
  overrides :c:member:`~PyTypeObject.tp_new` is deprecated.
  Call the metaclass instead.

.. Add deprecations above alphabetically, not here at the end.

.. include:: ../deprecations/c-api-pending-removal-in-3.14.rst

.. include:: ../deprecations/c-api-pending-removal-in-3.15.rst

.. include:: ../deprecations/c-api-pending-removal-in-future.rst

Removed
-------

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

* Legacy Unicode APIs have been removed. See :pep:`623` for detail.

  * :c:macro:`!PyUnicode_WCHAR_KIND`
  * :c:func:`!PyUnicode_AS_UNICODE`
  * :c:func:`!PyUnicode_AsUnicode`
  * :c:func:`!PyUnicode_AsUnicodeAndSize`
  * :c:func:`!PyUnicode_AS_DATA`
  * :c:func:`!PyUnicode_FromUnicode`
  * :c:func:`!PyUnicode_GET_SIZE`
  * :c:func:`!PyUnicode_GetSize`
  * :c:func:`!PyUnicode_GET_DATA_SIZE`

* Remove the ``PyUnicode_InternImmortal()`` function macro.
  (Contributed by Victor Stinner in :gh:`85858`.)

Notable changes in 3.12.4
=========================

ipaddress
---------

* Fixed ``is_global`` and ``is_private`` behavior in ``IPv4Address``,
  ``IPv6Address``, ``IPv4Network`` and ``IPv6Network``.


Notable changes in 3.12.5
=========================

email
-----


* Headers with embedded newlines are now quoted on output.

  The :mod:`~email.generator` will now refuse to serialize (write) headers
  that are improperly folded or delimited, such that they would be parsed as
  multiple headers or joined with adjacent data.
  If you need to turn this safety feature off,
  set :attr:`~email.policy.Policy.verify_generated_headers`.
  (Contributed by Bas Bloemsaat and Petr Viktorin in :gh:`121650`.)
