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****************************
What's New In Python 3.12
****************************
:Release: |release|
:Date: |today|
.. 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.
For full details, see the :ref:`changelog <changelog>`.
.. note::
Prerelease users should be aware that this document is currently in draft
form. It will be updated substantially as Python 3.12 moves towards release,
so it's worth checking back even after reading earlier versions.
Summary -- Release highlights
=============================
.. This section singles out the most important changes in Python 3.12.
Brevity is key.
.. PEP-sized items next.
New grammar features:
* :pep:`701`: Syntactic formalization of f-strings
New typing features:
* :pep:`688`: Making the buffer protocol accessible in Python
* :ref:`whatsnew312-pep692`
* :pep:`698`: Override Decorator for Static Typing
Important deprecations, removals or restrictions:
* :pep:`623`: Remove wstr from Unicode
* :pep:`632`: Remove the ``distutils`` package
Improved Error Messages
=======================
* Modules from the standard library are now potentially suggested as part of
the error messages displayed by the interpreter when a :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
============
.. _whatsnew312-pep701:
PEP 701: Syntactic formalization of f-strings
---------------------------------------------
:pep:`701` lifts some restrictions on the usage of f-strings. Expression components
inside f-strings can now be any valid Python expression including backslashes,
unicode escaped sequences, multi-line expressions, comments and strings reusing the
same quote as the containing f-string. Let's cover these in detail:
* Quote reuse: in Python 3.11, reusing the same quotes as the containing f-string
raises a :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-strings expressions
must be defined in a single line even if outside f-strings expressions could
span multiple lines (like literal lists being defined over multiple lines),
making them harder to read. In Python 3.12 you can now define expressions
spaning multiple lines and include comments on them:
>>> f"This is the playlist: {", ".join([
... 'Take me back to Eden', # My, my, those eyes like fire
... 'Alkaline', # Not acid nor alkaline
... 'Ascensionism' # Take to the broken skies at last
... ])}"
'This is the playlist: Take me back to Eden, Alkaline, Ascensionism'
* Backslashes and unicode characters: before Python 3.12 f-string expressions
couldn't contain any ``\`` character. This also affected unicode escaped
sequences (such as ``\N{snowman}``) as these contain the ``\N`` part that
previously could not be part of expression components of f-strings. Now, you
can define expressions like this:
>>> print(f"This is the playlist: {"\n".join(songs)}")
This is the playlist: Take me back to Eden
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.
(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-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 2x.
Comprehension iteration variables remain isolated; they don't overwrite a
variable of the same name in the outer scope, nor are they visible after the
comprehension. This isolation is now maintained via stack/locals manipulation,
not via separate function scope.
Inlining does result in a few visible behavior changes:
* There is no longer a separate frame for the comprehension in tracebacks,
and tracing/profiling no longer shows the comprehension as a function call.
* Calling :func:`locals` inside a comprehension now includes variables
from outside the comprehension, and no longer includes the synthetic ``.0``
variable for the comprehension "argument".
Contributed by Carl Meyer and Vladimir Matveev in :pep:`709`.
PEP 688: Making the buffer protocol accessible in Python
--------------------------------------------------------
:pep:`688` introduces a way to use the :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`.)
New Features Related to Type Hints
==================================
This section covers major changes affecting :pep:`484` type hints 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.
This PEP 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.
(PEP written by Franek Magiera)
Other Language Changes
======================
* Add :ref:`perf_profiling` through the new
environment variable :envvar:`PYTHONPERFSUPPORT`,
the new 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` APIs.
(Design by Pablo Galindo. Contributed by Pablo Galindo and Christian Heimes
with contributions from Gregory P. Smith [Google] and Mark Shannon
in :gh:`96123`.)
* The extraction methods in :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-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`.)
* :class:`memoryview` now supports the half-float type (the "e" format code).
(Contributed by Dong-hee Na and Antoine Pitrou in :gh:`90751`.)
* The parser now raises :exc:`SyntaxError` when parsing source code containing
null bytes. (Contributed by Pablo Galindo in :gh:`96670`.)
* :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 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`.)
* 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`.)
* 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`.)
* 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`.)
* :class:`slice` objects are now hashable, allowing them to be used as dict keys and
set items. (Contributed by Will Bradshaw and Furkan Onder in :gh:`101264`.)
* Exceptions raised in a typeobject'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`.)
New Modules
===========
* None yet.
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`.)
* Added :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 O 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 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. It is recommended to not manually
configure a child watcher as the event loop now uses the best available
child watcher for each platform (:class:`~asyncio.PidfdChildWatcher`
if supported and :class:`~asyncio.ThreadedChildWatcher` otherwise).
(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`.)
* 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 Ostricher 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`.
(Contributed by Prince Roshan in :gh:`103636`.)
csv
---
* Add :data:`~csv.QUOTE_NOTNULL` and :data:`~csv.QUOTE_STRINGS` flags to
provide finer grained control of ``None`` and empty strings by
:class:`~csv.writer` objects.
inspect
-------
* Add :func:`inspect.markcoroutinefunction` to mark sync functions that return
a :term:`coroutine` for use with :func:`inspect.iscoroutinefunction`.
(Contributed 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 :issue:`35759`.)
* 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, and some may be 6x faster or more. (Contributed by Alex
Waygood in :gh:`103193`.)
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 :issue:`40358`.)
* 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.
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`.)
fractions
---------
* Objects of type :class:`fractions.Fraction` now support float-style
formatting. (Contributed by Mark Dickinson in :gh:`100161`.)
itertools
---------
* Added :class:`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
----
* Added :func:`math.sumprod` for computing a sum of products.
(Contributed by Raymond Hettinger in :gh:`100485`.)
os
--
* Add :data:`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`.)
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`.)
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`.)
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 and
will be removed in Python 3.14.
(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`.)
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`.)
unicodedata
-----------
* The Unicode database has been updated to version 15.0.0. (Contributed by
Benjamin Peterson in :gh:`96734`).
unittest
--------
Added ``--durations`` command line option, showing the N slowest test cases::
python3 -m unittest --durations=3 lib.tests.test_threading
.....
Slowest test durations
----------------------------------------------------------------------
1.210s test_timeout (Lib.test.test_threading.BarrierTests)
1.003s test_default_timeout (Lib.test.test_threading.BarrierTests)
0.518s test_timeout (Lib.test.test_threading.EventTests)
(0.000 durations hidden. Use -v to show these durations.)
----------------------------------------------------------------------
Ran 158 tests in 9.869s
OK (skipped=3)
(Contributed by Giampaolo Rodola in :issue:`4080`)
uuid
----
* Add a :ref:`command-line interface <uuid-cli>`.
(Contributed by Adam Chhina in :gh:`88597`.)
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.
.. _whatsnew-typing-py312:
typing
------
* Add :func:`typing.override`, an override decorator telling to static type
checkers to verify that a method overrides some method or attribute of the
same name on a base class, as per :pep:`698`. (Contributed by Steven Troxler in
:gh:`101564`.)
* :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 fourteen
or more members may be slower than in Python 3.11. (Contributed by Alex
Waygood in :gh:`74690` and :gh:`103193`.)
sys
---
* 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`.)
Optimizations
=============
* Removed ``wstr`` and ``wstr_length`` members from Unicode objects.
It reduces object size by 8 or 16 bytes on 64bit platform. (:pep:`623`)
(Contributed by Inada Naoki in :gh:`92536`.)
* Added experimental support for using the BOLT binary optimizer in the build
process, which improves performance by 1-5%.
(Contributed by Kevin Modzelewski in :gh:`90536` and tuned by Dong-hee Na in :gh:`101525`)
* Speed up the regular expression substitution (functions :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 O 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`.)
CPython bytecode changes
========================
* Removed 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`.)
* Removed the :opcode:`!JUMP_IF_FALSE_OR_POP` and :opcode:`!JUMP_IF_TRUE_OR_POP`
instructions. (Contributed by Irit Katriel in :gh:`102859`.)
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
==========
* :class:`typing.Hashable` and :class:`typing.Sized` aliases for :class:`collections.abc.Hashable`
and :class:`collections.abc.Sized`. (:gh:`94309`.)
* The :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`.)
* The 3-arg signatures (type, value, traceback) of :meth:`~coroutine.throw`,
:meth:`~generator.throw` and :meth:`~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`.)
* 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`.)
* The :mod:`xml.etree.ElementTree` 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.
* 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.)
* 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`.)
* 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`.)
* The *onerror* argument of :func:`shutil.rmtree` is deprecated as will be removed
in Python 3.14. Use *onexc* instead. (Contributed by Irit Katriel in :gh:`102828`.)
* 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.
* ``calendar.January`` and ``calendar.February`` constants are deprecated and
replaced by :data:`calendar.Month.JANUARY` and :data:`calendar.Month.FEBRUARY`.
(Contributed by Prince Roshan in :gh:`103636`.)
* The bitwise inversion operator (``~``) on bool is deprecated. It will throw an
error in Python 3.14. 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 with ``~int(x)``. (Contributed by Tim Hoffmann
in :gh:`103487`.)
* :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
:attr:`datetime.UTC`.
(Contributed by Paul Ganssle in :gh:`103857`.)
Pending Removal in Python 3.13
------------------------------
The following modules and APIs have been deprecated in earlier Python releases,
and will be removed in Python 3.13.
Modules (see :pep:`594`):
* :mod:`aifc`
* :mod:`audioop`
* :mod:`!cgi`
* :mod:`!cgitb`
* :mod:`chunk`
* :mod:`crypt`
* :mod:`imghdr`
* :mod:`!mailcap`
* :mod:`msilib`
* :mod:`!nis`
* :mod:`!nntplib`
* :mod:`!ossaudiodev`
* :mod:`!pipes`
* :mod:`!sndhdr`
* :mod:`!spwd`
* :mod:`!sunau`
* :mod:`!telnetlib`
* :mod:`uu`
* :mod:`!xdrlib`
APIs:
* :class:`!configparser.LegacyInterpolation` (:gh:`90765`)
* :func:`locale.getdefaultlocale` (:gh:`90817`)
* :meth:`!turtle.RawTurtle.settiltangle` (:gh:`50096`)
* :func:`!unittest.findTestCases` (:gh:`50096`)
* :func:`!unittest.makeSuite` (:gh:`50096`)
* :func:`!unittest.getTestCaseNames` (:gh:`50096`)
* :class:`!webbrowser.MacOSX` (:gh:`86421`)
Pending Removal in Python 3.14
------------------------------
* Deprecated the following :mod:`importlib.abc` 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`.)
* 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`.)
* :class:`typing.ByteString`, deprecated since Python 3.9, now causes a
:exc:`DeprecationWarning` to be emitted when it is used.
* Creating immutable types (:data:`Py_TPFLAGS_IMMUTABLETYPE`) with mutable
bases using the C API.
* Deprecated the *isdst* parameter in :func:`email.utils.localtime`.
(Contributed by Alan Williams in :gh:`72346`.)
* ``__package__`` and ``__cached__`` will cease to be set or taken
into consideration by the import system (:gh:`97879`).
* Testing the truth value of an :class:`xml.etree.ElementTree.Element`
is deprecated and will raise an exception 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:`multiprocessing-start-methods`.
* :mod:`pty` 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.
* Accessing ``co_lnotab`` was deprecated in :pep:`626` since 3.10
and was planned to be removed in 3.12
but it only got a proper :exc:`DeprecationWarning` in 3.12.
May be removed in 3.14.
(Contributed by Nikita Sobolev in :gh:`101866`.)
* The *onerror* argument of :func:`shutil.rmtree` is deprecated in 3.12,
and will be removed in 3.14.
* 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`.)
* :func:`pkgutil.find_loader` and :func:`pkgutil.get_loader`
now raise :exc:`DeprecationWarning`;
use :func:`importlib.util.find_spec` instead.
(Contributed by Nikita Sobolev in :gh:`97850`.)
* 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`.)
Pending Removal in Future Versions
----------------------------------
The following APIs were deprecated in earlier Python versions and will be removed,
although there is currently no date scheduled for their removal.
* :class:`typing.Text` (:gh:`92332`)
* Currently Python accepts numeric literals immediately followed by keywords,
for example ``0in x``, ``1or x``, ``0if 1else 2``. It allows confusing
and ambiguous expressions like ``[0x1for x in y]`` (which can be
interpreted as ``[0x1 for x in y]`` or ``[0x1f or x in y]``).
A syntax warning is raised if the numeric literal is
immediately followed by one of keywords :keyword:`and`, :keyword:`else`,
:keyword:`for`, :keyword:`if`, :keyword:`in`, :keyword:`is` and :keyword:`or`.
In a future release it will be changed to a syntax error. (:gh:`87999`)
Removed
=======
* Remove the ``distutils`` package. It was deprecated in Python 3.10 by
:pep:`632` "Deprecate distutils module". For projects still using
``distutils`` and cannot be updated to something else, the ``setuptools``
project can be installed: it still provides ``distutils``.
(Contributed by Victor Stinner in :gh:`92584`.)
* Remove the bundled setuptools wheel from :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`.)
* Removed many old deprecated :mod:`unittest` features:
- 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 3.2).
- An alias of the :class:`~unittest.TextTestResult` class:
``_TextTestResult`` (deprecated in Python 3.2).
(Contributed by Serhiy Storchaka in :issue:`45162`.)
* 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.
* 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`.)
* ``smtpd`` has been removed according to the schedule in :pep:`594`,
having been deprecated in Python 3.4.7 and 3.5.4.
Use aiosmtpd_ PyPI module or any other
:mod:`asyncio`-based server instead.
(Contributed by Oleg Iarygin in :gh:`93243`.)
.. _aiosmtpd: https://pypi.org/project/aiosmtpd/
* ``asynchat`` and ``asyncore`` 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`.)
* Remove ``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`.)
* Remove the :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`.)
* :mod:`gzip`: Remove the ``filename`` attribute of :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`.)
* 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:`!locale.format` function, deprecated in Python 3.7:
use :func:`locale.format_string` instead.
(Contributed by Victor Stinner in :gh:`94226`.)
* :mod:`hashlib`: Remove the pure Python implementation of
: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`.)
* :mod:`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`.)
* :mod:`zipimport`: Remove ``find_loader()`` and ``find_module()`` methods,
deprecated in Python 3.10: use the ``find_spec()`` method instead. See
:pep:`451` for the rationale.
(Contributed by Victor Stinner in :gh:`94379`.)
* Remove the :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 server hostname. Code is subject to `CWE-295
<https://cwe.mitre.org/data/definitions/295.html>`_: Improper Certificate
Validation.
(Contributed by Victor Stinner in :gh:`94199`.)
* 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`` has been removed. (Contributed by Brett
Cannon in :gh:`65961`.)
* Support for ``find_loader()`` and ``find_module()`` APIs have been
removed. (Contributed by Barry Warsaw in :gh:`98040`.)
* ``importlib.abc.Finder``, ``pkg.ImpImporter``, and ``pkg.ImpLoader`` have
been removed. (Contributed by Barry Warsaw in :gh:`98040`.)
* The :mod:`!imp` module has been removed. (Contributed by Barry Warsaw in
:gh:`98040`.)
* Removed the ``suspicious`` rule from the documentation Makefile, and
removed ``Doc/tools/rstlint.py``, both in favor of `sphinx-lint
<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`.)
* :mod:`ftplib`: Remove the ``FTP_TLS.ssl_version`` class attribute: use the
*context* parameter instead.
(Contributed by Victor Stinner in :gh:`94172`.)
* Remove support for obsolete browsers from :mod:`webbrowser`.
Removed browsers include: Grail, Mosaic, Netscape, Galeon, Skipstone,
Iceape, Firebird, and Firefox versions 35 and below (:gh:`102871`).
.. _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`.)
* Removed ``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-integral 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.
* Removed the ``asyncore``-based ``smtpd`` module deprecated in Python 3.4.7
and 3.5.4. A recommended replacement is the
:mod:`asyncio`-based 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 Dong-hee 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``,
``FSRING_MIDDLE`` and ``FSTRING_END`` are now emitted for f-string "string"
parts in addition to the appropriate tokens for the tokenization in the
expression components. For example for the f-string ``f"start {1+1} end"``
the old version of the tokenizer emitted::
1,0-1,18: STRING 'f"start {1+1} end"'
while the new version emits::
1,0-1,2: FSTRING_START 'f"'
1,2-1,8: FSTRING_MIDDLE 'start '
1,8-1,9: OP '{'
1,9-1,10: NUMBER '1'
1,10-1,11: OP '+'
1,11-1,12: NUMBER '1'
1,12-1,13: OP '}'
1,13-1,17: FSTRING_MIDDLE ' end'
1,17-1,18: FSTRING_END '"'
Aditionally, there may be some minor behavioral changes as a consecuence of the
changes required to support :pep:`701`. Some of these changes include:
* Some final ``DEDENT`` tokens are now emitted within the bounds of the
input. This means that for a file containing 3 lines, the old version of the
tokenizer returned a ``DEDENT`` token in line 4 whilst the new version returns
the token in line 3.
* The ``type`` attribute of the tokens emitted when tokenizing some invalid Python
characters such as ``!`` has changed from ``ERRORTOKEN`` to ``OP``.
Build Changes
=============
* Python no longer uses ``setup.py`` to build shared C extension modules.
Build parameters like headers and libraries are detected in ``configure``
script. Extensions are built by ``Makefile``. Most extensions use
``pkg-config`` and fall back to manual detection.
(Contributed by Christian Heimes in :gh:`93939`.)
* ``va_start()`` with two parameters, like ``va_start(args, format),``
is now required to build Python.
``va_start()`` is no longer called with a single parameter.
(Contributed by Kumar Aditya in :gh:`93207`.)
* CPython now uses the ThinLTO option as the default link time optimization policy
if the Clang compiler accepts the flag.
(Contributed by Dong-hee Na in :gh:`89536`.)
* Add ``COMPILEALL_OPTS`` variable in Makefile to override :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.
C API Changes
=============
New Features
------------
* :pep:`697`: Introduced 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`: Added 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.
- :const:`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`.)
* Added the new 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>`:
* :const:`Py_TPFLAGS_HAVE_VECTORCALL`
* :c:func:`PyVectorcall_NARGS`
* :c:func:`PyVectorcall_Call`
* :c:type:`vectorcallfunc`
The :const:`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, :const:`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 :const:`Py_TPFLAGS_MANAGED_DICT` and :const:`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`
* :const:`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`.)
* Added 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`.)
* Added 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`.)
* Added :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`.)
* Added :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 Ostricher 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`).
* :pep:`683`: Introduced Immortal Objects to Python which allows objects
to bypass reference counts and introduced 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 refleak.py to
correctly track reference counts and allocated blocks
(Contributed by Eddie Elizondo in :gh:`84436`.)
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, ``intmax_t``, ``ptrdiff_t``, ``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`.)
* Fixed 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 :const:`Py_TPFLAGS_MANAGED_DICT` and
:const:`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 :const:`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 compabitility. Note that it is an internal global and only
available on debug builds. If you happen to be using it then you'll
need to start using ``_Py_GetGlobalRefTotal()``.
* The following functions now select an appropriate metaclass for the newly
created type:
* :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``.
* :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.
Deprecated
----------
* 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_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 immutable types (:const:`Py_TPFLAGS_IMMUTABLETYPE`) with mutable
bases is deprecated and will be disabled in Python 3.14.
* The ``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 ``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 ``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 ``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.
Removed
-------
* Remove the ``token.h`` header file. There was never any public tokenizer C
API. The ``token.h`` header file was only designed to be used by Python
internals.
(Contributed by Victor Stinner in :gh:`92651`.)
* Legacy Unicode APIs have been removed. See :pep:`623` for detail.
* :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`.)
* 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`.)
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