cpython/Misc/NEWS.d/3.15.0a3.rst

.. date: 2025-11-18-13-55-47
.. gh-issue: 141692
.. nonce: tud9if
.. release date: 2025-12-16
.. section: Tools/Demos

Each slice of an iOS XCframework now contains a ``lib`` folder that contains
a symlink to the libpython dylib. This allows binary modules to be compiled
for iOS using dynamic libreary linking, rather than Framework linking.

..

.. date: 2025-10-27-15-53-47
.. gh-issue: 140381
.. nonce: N5o3pa
.. section: Tests

Fix flaky test_profiling tests on i686 and s390x architectures by increasing
slow_fibonacci call frequency from every 5th iteration to every 2nd
iteration.

..

.. date: 2025-10-16-15-08-58
.. gh-issue: 140210
.. nonce: P9vUP8
.. section: Tests

Make ``test_sysconfig.test_parse_makefile_renamed_vars`` less fragile by
clearing the environment variables before parsing the Makefile.

..

.. date: 2025-12-01-09-36-45
.. gh-issue: 142145
.. nonce: tcAUhg
.. section: Security

Remove quadratic behavior in ``xml.minidom`` node ID cache clearing.

..

.. date: 2025-11-13-22-31-56
.. gh-issue: 42400
.. nonce: pqB5Kq
.. section: Security

Fix buffer overflow in ``_Py_wrealpath()`` for paths exceeding
``MAXPATHLEN`` bytes by using dynamic memory allocation instead of
fixed-size buffer. Patch by Shamil Abdulaev.

..

.. date: 2024-05-23-11-47-48
.. gh-issue: 119451
.. nonce: qkJe9-
.. section: Security

Fix a potential memory denial of service in the :mod:`http.client` module.
When connecting to a malicious server, it could cause an arbitrary amount of
memory to be allocated. This could have led to symptoms including a
:exc:`MemoryError`, swapping, out of memory (OOM) killed processes or
containers, or even system crashes.

..

.. date: 2024-05-21-22-11-31
.. gh-issue: 119342
.. nonce: BTFj4Z
.. section: Security

Fix a potential memory denial of service in the :mod:`plistlib` module. When
reading a Plist file received from untrusted source, it could cause an
arbitrary amount of memory to be allocated. This could have led to symptoms
including a :exc:`MemoryError`, swapping, out of memory (OOM) killed
processes or containers, or even system crashes.

..

.. date: 2025-12-16-11-55-55
.. gh-issue: 142754
.. nonce: xuCrt3
.. section: Library

Add the *ownerDocument* attribute to :mod:`xml.dom.minidom` elements and
attributes created by directly instantiating the ``Element`` or ``Attr``
class. Note that this way of creating nodes is not supported; creator
functions like :py:meth:`xml.dom.Document.documentElement` should be used
instead.

..

.. date: 2025-12-14-18-30-48
.. gh-issue: 142594
.. nonce: belDmD
.. section: Library

Fix crash in ``TextIOWrapper.close()`` when the underlying buffer's
``closed`` property calls :meth:`~io.TextIOBase.detach`.

..

.. date: 2025-12-13-21-19-28
.. gh-issue: 76007
.. nonce: 6fs_gT
.. section: Library

Deprecate ``__version__`` from :mod:`ctypes`. Patch by Hugo van Kemenade.

..

.. date: 2025-12-13-19-17-01
.. gh-issue: 76007
.. nonce: -OSQU3
.. section: Library

Deprecate ``__version__`` from :mod:`wsgiref.simple_server`. Patch by Hugo
van Kemenade.

..

.. date: 2025-12-13-06-17-44
.. gh-issue: 142651
.. nonce: ZRtBu4
.. section: Library

:mod:`unittest.mock`: fix a thread safety issue where :attr:`Mock.call_count
<unittest.mock.Mock.call_count>` may return inaccurate values when the mock
is called concurrently from multiple threads.

..

.. date: 2025-12-13-00-09-09
.. gh-issue: 76007
.. nonce: Xg1xCO
.. section: Library

Deprecate ``__version__`` from :mod:`http.server`. Patch by Hugo van
Kemenade.

..

.. date: 2025-12-12-15-14-03
.. gh-issue: 138122
.. nonce: m3EF9E
.. section: Library

Add ``--subprocesses`` flag to :mod:`profiling.sampling` CLI to
automatically profile subprocesses spawned by the target. When enabled, the
profiler monitors for new Python subprocesses and profiles each one
separately, writing results to individual output files. This is useful for
profiling applications that use :mod:`multiprocessing`,
:class:`~concurrent.futures.ProcessPoolExecutor`, or other subprocess-based
parallelism. Patch by Pablo Galindo.

..

.. date: 2025-12-12-02-56-26
.. gh-issue: 142595
.. nonce: wHvTqq
.. section: Library

Added type check during initialization of the :mod:`decimal` module to
prevent a crash in case of broken stdlib.  Patch by Sergey B Kirpichev.

..

.. date: 2025-12-11-09-03-07
.. gh-issue: 142556
.. nonce: RuiBte
.. section: Library

Fix crash when a task gets re-registered during finalization in
:mod:`asyncio`. Patch by Kumar Aditya.

..

.. date: 2025-12-11-04-18-49
.. gh-issue: 138122
.. nonce: m3EF9E
.. section: Library

Add ``--mode=exception`` to the sampling profiler to capture samples only
from threads with an active exception, useful for analyzing exception
handling overhead. Patch by Pablo Galindo.

..

.. date: 2025-12-10-21-19-10
.. gh-issue: 142539
.. nonce: _8Vzr0
.. section: Library

:mod:`traceback`: Fix location of carets in :exc:`SyntaxError`\s when the
source contains wide characters.

..

.. date: 2025-12-10-11-20-05
.. gh-issue: 123241
.. nonce: oYg2n7
.. section: Library

Avoid reference count operations in garbage collection of :mod:`ctypes`
objects.

..

.. date: 2025-12-10-11-02-53
.. gh-issue: 142451
.. nonce: eCLvhG
.. section: Library

:mod:`hmac`: correctly copy :class:`~hmac.HMAC` attributes for objects
copied through :meth:`HMAC.copy() <hmac.HMAC.copy>`. Patch by Bénédikt Tran.

..

.. date: 2025-12-09-22-11-59
.. gh-issue: 138122
.. nonce: CsoBEo
.. section: Library

The ``profiling.sampling`` flamegraph profiler now supports inverted
flamegraph view that aggregates all leaf nodes. In a standard flamegraph, if
a hot function is called from multiple locations, it appears multiple times
as separate leaf nodes. In the inverted flamegraph, all occurrences of the
same leaf function are merged into a single aggregated node at the root,
showing the total hotness of that function in one place. The children of
each aggregated node represent its callers, making it easier to identify
which functions consume the most CPU time and where they are called from.

..

.. date: 2025-12-09-14-40-45
.. gh-issue: 112527
.. nonce: Tvf5Zk
.. section: Library

The help text for required options in :mod:`argparse` no longer extended
with " (default: None)".

..

.. date: 2025-12-08-18-12-44
.. gh-issue: 142438
.. nonce: UF_0nd
.. section: Library

Fixed a possible leaked GIL in _PySSL_keylog_callback.

..

.. date: 2025-12-07-23-21-13
.. gh-issue: 138122
.. nonce: m3EF9E
.. section: Library

Add bytecode-level instruction profiling to the sampling profiler via the
new ``--opcodes`` flag. When enabled, the profiler captures which bytecode
opcode is executing at each sample, including Python 3.11+ adaptive
specializations, and visualizes this data in the heatmap, flamegraph, gecko,
and live output formats. Patch by Pablo Galindo

..

.. date: 2025-12-07-22-13-28
.. gh-issue: 142389
.. nonce: J9v904
.. section: Library

Add backtick markup support in :mod:`argparse` description and epilog text
to highlight inline code when color output is enabled.

..

.. date: 2025-12-07-17-30-05
.. gh-issue: 142346
.. nonce: okcAAp
.. section: Library

Fix usage formatting for mutually exclusive groups in :mod:`argparse` when
they are preceded by positional arguments or followed or intermixed with
other optional arguments.

..

.. date: 2025-12-07-13-37-18
.. gh-issue: 142374
.. nonce: m3EF9E
.. section: Library

Fix cumulative percentage calculation for recursive functions in the new
sampling profiler. When profiling recursive functions, cumulative statistics
(cumul%, cumtime) could exceed 100% because each recursive frame in a stack
was counted separately. For example, a function recursing 500 times in every
sample would show 50000% cumulative presence. The fix deduplicates locations
within each sample so cumulative stats correctly represent "percentage of
samples where this function was on the stack". Patch by Pablo Galindo.

..

.. date: 2025-12-07-02-36-24
.. gh-issue: 142315
.. nonce: 02o5E_
.. section: Library

Pdb can now run scripts from anonymous pipes used in process substitution.
Patch by Bartosz Sławecki.

..

.. date: 2025-12-06-16-45-34
.. gh-issue: 64532
.. nonce: 4OXZpF
.. section: Library

Subparser help now includes required optional arguments from the parent
parser in the usage, making it clearer what arguments are needed to run a
subcommand. Patch by Savannah Ostrowski.

..

.. date: 2025-12-06-13-19-43
.. gh-issue: 142207
.. nonce: x_X9oH
.. section: Library

Fix: profiling.sampling may cause assertion ``!(has_gil && gil_requested)``

..

.. date: 2025-12-06-13-02-13
.. gh-issue: 142332
.. nonce: PNvXCV
.. section: Library

Fix usage formatting for positional arguments in mutually exclusive groups
in :mod:`argparse`. in :mod:`argparse`.

..

.. date: 2025-12-05-18-26-50
.. gh-issue: 142282
.. nonce: g6RQUN
.. section: Library

Fix :func:`winreg.QueryValueEx` to not accidentally read garbage buffer
under race condition.

..

.. date: 2025-12-05-18-25-29
.. gh-issue: 142318
.. nonce: EzcQ3N
.. section: Library

Fix typing ``'q'`` at the help of the interactive tachyon profiler exiting
the profiler.

..

.. date: 2025-12-05-16-39-17
.. gh-issue: 75949
.. nonce: pHxW98
.. section: Library

Fix :mod:`argparse` to preserve ``|`` separators in mutually exclusive
groups when the usage line wraps due to length.

..

.. date: 2025-12-04-23-26-12
.. gh-issue: 142267
.. nonce: yOM6fP
.. section: Library

Improve :mod:`argparse` performance by caching the formatter used for
argument validation.

..

.. date: 2025-12-04-23-24-24
.. gh-issue: 139862
.. nonce: NBfsD4
.. section: Library

Remove ``color`` parameter from :class:`!argparse.HelpFormatter`
constructor. Color is controlled by :class:`~argparse.ArgumentParser`.

..

.. date: 2025-12-04-09-22-31
.. gh-issue: 68552
.. nonce: I_v-xB
.. section: Library

``MisplacedEnvelopeHeaderDefect`` and ``Missing header name`` defects are
now correctly passed to the ``handle_defect`` method of ``policy`` in
:class:`~email.parser.FeedParser`.

..

.. date: 2025-12-03-09-36-29
.. gh-issue: 142206
.. nonce: ilwegH
.. section: Library

The resource tracker in the :mod:`multiprocessing` module can now understand
messages from older versions of itself. This avoids issues with upgrading
Python while it is running. (Note that such 'in-place' upgrades are not
tested.)

..

.. date: 2025-12-03-06-12-39
.. gh-issue: 142214
.. nonce: appYNZ
.. section: Library

Fix two regressions in :mod:`dataclasses` in Python 3.14.1 related to
annotations.

* An exception is no longer raised if ``slots=True`` is used and the
  ``__init__`` method does not have an ``__annotate__`` attribute
  (likely because ``init=False`` was used).

* An exception is no longer raised if annotations are requested on the
  ``__init__`` method and one of the fields is not present in the class
  annotations. This can occur in certain dynamic scenarios.

Patch by Jelle Zijlstra.

..

.. date: 2025-12-02-14-52-51
.. gh-issue: 142203
.. nonce: ofWOvV
.. section: Library

Remove the *debug_override* parameter from
:func:`importlib.util.cache_from_source` which has been deprecated since
Python 3.5.

..

.. date: 2025-12-01-14-43-58
.. gh-issue: 138122
.. nonce: nRm3ic
.. section: Library

The ``_remote_debugging`` module now implements frame caching in the
``RemoteUnwinder`` class to reduce memory reads when profiling remote
processes. When ``cache_frames=True``, unchanged portions of the call stack
are reused from previous samples, significantly improving profiling
performance for deep call stacks.

..

.. date: 2025-12-01-10-03-08
.. gh-issue: 116738
.. nonce: 972YsG
.. section: Library

Fix :mod:`cmath` data race when initializing trigonometric tables with
subinterpreters.

..

.. date: 2025-11-30-04-28-30
.. gh-issue: 141982
.. nonce: pxZct9
.. section: Library

Allow :mod:`pdb` to set breakpoints on async functions with function names.

..

.. date: 2025-11-29-04-20-44
.. gh-issue: 74389
.. nonce: pW3URj
.. section: Library

When the stdin being used by a :class:`subprocess.Popen` instance is closed,
this is now ignored in :meth:`subprocess.Popen.communicate` instead of
leaving the class in an inconsistent state.

..

.. date: 2025-11-29-03-02-45
.. gh-issue: 87512
.. nonce: bn4xbm
.. section: Library

Fix :func:`subprocess.Popen.communicate` timeout handling on Windows when
writing large input. Previously, the timeout was ignored during stdin
writing, causing the method to block indefinitely if the child process did
not consume input quickly. The stdin write is now performed in a background
thread, allowing the timeout to be properly enforced.

..

.. date: 2025-11-28-08-25-19
.. gh-issue: 141939
.. nonce: BXPnFj
.. section: Library

Add color to all interpolated values in :mod:`argparse` help, like
``%(default)s`` or ``%(choices)s``. Patch by Alex Prengère.

..

.. date: 2025-11-27-20-16-38
.. gh-issue: 141473
.. nonce: Wq4xVN
.. section: Library

When :meth:`subprocess.Popen.communicate` was called with *input* and a
*timeout* and is called for a second time after a
:exc:`~subprocess.TimeoutExpired` exception before the process has died, it
should no longer hang.

..

.. date: 2025-11-27-11-39-50
.. gh-issue: 141999
.. nonce: _FKGlu
.. section: Library

Correctly allow :exc:`KeyboardInterrupt` to stop the process when using
:mod:`!profiling.sampling`.

..

.. date: 2025-11-27-10-49-13
.. gh-issue: 142006
.. nonce: nzJDG5
.. section: Library

Fix a bug in the :mod:`email.policy.default` folding algorithm which
incorrectly resulted in a doubled newline when a line ending at exactly
max_line_length was followed by an unfoldable token.

..

.. date: 2025-11-26-14-20-10
.. gh-issue: 141968
.. nonce: W139Pv
.. section: Library

Remove data copy from :mod:`re` compilation of regexes with large charsets
by using :meth:`bytearray.take_bytes`.

..

.. date: 2025-11-25-23-35-07
.. gh-issue: 141968
.. nonce: b3Gscp
.. section: Library

Remove data copy from :mod:`encodings.idna` :meth:`~codecs.Codec.encode` and
:meth:`~codecs.IncrementalEncoder.encode` by using
:meth:`bytearray.take_bytes`.

..

.. date: 2025-11-25-23-29-08
.. gh-issue: 141968
.. nonce: 0JnjXf
.. section: Library

Remove data copy from :mod:`codecs` ``punycode`` encoding by using
:meth:`bytearray.take_bytes`.

..

.. date: 2025-11-25-23-22-46
.. gh-issue: 141968
.. nonce: R1sHnJ
.. section: Library

Remove data copy from :func:`wave.Wave_read.readframes` and
:func:`wave.Wave_write.writeframes` by using :meth:`bytearray.take_bytes`.

..

.. date: 2025-11-25-22-54-07
.. gh-issue: 141968
.. nonce: vg3AMJ
.. section: Library

Remove a data copy from :func:`base64.b32decode` and
:func:`base64.b32encode` by using :meth:`bytearray.take_bytes`.

..

.. date: 2025-11-25-16-00-29
.. gh-issue: 59000
.. nonce: YtOyJy
.. section: Library

Fix :mod:`pdb` breakpoint resolution for class methods when the module
defining the class is not imported.

..

.. date: 2025-11-25-13-13-34
.. gh-issue: 116738
.. nonce: MnZRdV
.. section: Library

Fix thread safety issue with :mod:`re` scanner objects in free-threaded
builds.

..

.. date: 2025-11-24-14-05-52
.. gh-issue: 138122
.. nonce: 2bbGA8
.. section: Library

The ``profiling.sampling`` flamegraph profiler now displays thread status
statistics showing the percentage of time threads spend holding the GIL,
running without the GIL, waiting for the GIL, and performing garbage
collection. These statistics help identify GIL contention and thread
behavior patterns. When filtering by thread, the display shows per-thread
metrics.

..

.. date: 2025-11-24-06-44-45
.. gh-issue: 141781
.. nonce: MsK27r
.. section: Library

Fixed an issue where pdb.line_prefix assignment was ignored if assigned
after the module was imported.

..

.. date: 2025-11-22-16-33-48
.. gh-issue: 141863
.. nonce: 4PLhnv
.. section: Library

Update :ref:`asyncio-streams` to use :meth:`bytearray.take_bytes` for a over
10% performance improvement on pyperformance asyncio_tcp benchmark.

..

.. date: 2025-11-21-21-14-10
.. gh-issue: 141817
.. nonce: _v5LdB
.. section: Library

Add :data:`!socket.IPV6_HDRINCL` constant.

..

.. date: 2025-11-18-15-48-13
.. gh-issue: 105836
.. nonce: sbUw24
.. section: Library

Fix :meth:`asyncio.run_coroutine_threadsafe` leaving underlying cancelled
asyncio task running.

..

.. date: 2025-11-18-14-39-31
.. gh-issue: 141570
.. nonce: q3n984
.. section: Library

Support :term:`file-like object` raising :exc:`OSError` from
:meth:`~io.IOBase.fileno` in color detection (``_colorize.can_colorize()``).
This can occur when ``sys.stdout`` is redirected.

..

.. date: 2025-11-17-21-41-58
.. gh-issue: 141679
.. nonce: fs7zLJ
.. section: Library

Add colour to defaults in :mod:`argparse` help. Patch by Hugo van Kemenade.

..

.. date: 2025-11-17-16-53-49
.. gh-issue: 141686
.. nonce: V-xaoI
.. section: Library

Break reference cycles created by each call to :func:`json.dump` or
:meth:`json.JSONEncoder.iterencode`.

..

.. date: 2025-11-17-08-16-30
.. gh-issue: 141659
.. nonce: QNi9Aj
.. section: Library

Fix bad file descriptor errors from ``_posixsubprocess`` on AIX.

..

.. date: 2025-11-17-00-53-51
.. gh-issue: 141645
.. nonce: TC3TL3
.. section: Library

Add a new ``--live`` mode to the tachyon profiler in
:mod:`!profiling.sampling` module. This mode consist of a live TUI that
displays real-time profiling statistics as the target application runs,
similar to ``top``. Patch by Pablo Galindo

..

.. date: 2025-11-16-06-08-46
.. gh-issue: 141615
.. nonce: --6EK3
.. section: Library

Check ``stdin`` instead of ``stdout`` for ``use_rawinput`` in :mod:`pdb`.

..

.. date: 2025-11-16-04-40-06
.. gh-issue: 69113
.. nonce: Xy7Fmn
.. section: Library

Fix :mod:`doctest` to correctly report line numbers for doctests in
``__test__`` dictionary when formatted as triple-quoted strings by finding
unique lines in the string and matching them in the source file.

..

.. date: 2025-11-15-14-58-12
.. gh-issue: 141600
.. nonce: XY2BXg
.. section: Library

Fix musl version detection on Void Linux.

..

.. date: 2025-11-15-11-10-16
.. gh-issue: 48752
.. nonce: aB3xYz
.. section: Library

Add :func:`readline.get_pre_input_hook` function to retrieve the current
pre-input hook. This allows applications to save and restore the hook
without overwriting user settings. Patch by Sanyam Khurana.

..

.. date: 2025-11-14-18-00-41
.. gh-issue: 141565
.. nonce: Ap2bhJ
.. section: Library

Add async-aware profiling to the Tachyon sampling profiler. The profiler now
reconstructs and displays async task hierarchies in flamegraphs, making the
output more actionable for users. Patch by Savannah Ostrowski and Pablo
Galindo Salgado.

..

.. date: 2025-11-13-13-11-02
.. gh-issue: 60107
.. nonce: LZq3QF
.. section: Library

Remove a copy from :meth:`io.RawIOBase.read`. If the underlying I/O class
keeps a reference to the mutable memory, raise a :exc:`BufferError`.

..

.. date: 2025-11-10-00-14-20
.. gh-issue: 116738
.. nonce: IxliC_
.. section: Library

Make csv module thread-safe on the :term:`free threaded <free threading>`
build.

..

.. date: 2025-11-03-17-13-00
.. gh-issue: 140911
.. nonce: 7KFvSQ
.. section: Library

:mod:`collections`: Ensure that the methods ``UserString.rindex()`` and
``UserString.index()`` accept :class:`collections.UserString` instances as
the sub argument.

..

.. date: 2025-11-02-10-44-23
.. gh-issue: 140875
.. nonce: wt6B37
.. section: Library

Fix handling of unclosed character references (named and numerical) followed
by the end of file in :class:`html.parser.HTMLParser` with
``convert_charrefs=False``.

..

.. date: 2025-10-27-17-00-11
.. gh-issue: 140677
.. nonce: hM9pTq
.. section: Library

Add heatmap visualization mode to the Tachyon sampling profiler. The new
``--heatmap`` output format provides a line-by-line view showing execution
intensity with color-coded samples, inline statistics, and interactive call
graph navigation between callers and callees.

..

.. date: 2025-10-23-06-38-35
.. gh-issue: 139946
.. nonce: HZa5hu
.. section: Library

Distinguish stdout and stderr when colorizing output in argparse module.

..

.. date: 2025-10-12-12-43-56
.. gh-issue: 76007
.. nonce: PyGM14
.. section: Library

:mod:`pydoc`: Fix :exc:`DeprecationWarning` being raised when generating doc
for :term:`stdlib` modules.

..

.. date: 2025-10-09-15-46-18
.. gh-issue: 139686
.. nonce: XwIZB2
.. section: Library

Make importlib.reload no-op for lazy modules.

..

.. date: 2025-09-09-13-00-42
.. gh-issue: 138697
.. nonce: QVwJw_
.. section: Library

Fix inferring *dest* from a single-dash long option in :mod:`argparse`. If a
short option and a single-dash long option are passed to
:meth:`!add_argument`, *dest* is now inferred from the single-dash long
option.

..

.. date: 2025-09-09-10-13-24
.. gh-issue: 138525
.. nonce: hDTaAM
.. section: Library

Add support for single-dash long options and alternate prefix characters in
:class:`argparse.BooleanOptionalAction`.

..

.. date: 2025-07-29-11-37-22
.. gh-issue: 79986
.. nonce: fnJbE_
.. section: Library

Add parsing for ``References`` and ``In-Reply-To`` headers to the
:mod:`email` library that parses the header content as lists of message id
tokens.  This prevents them from being folded incorrectly.

..

.. date: 2025-07-10-18-40-11
.. gh-issue: 135559
.. nonce: BMDtYn
.. section: Library

Flag: a ``dir()`` on a ``Flag`` enumeration now shows non-canonical members.
(i.e. aliases).

..

.. date: 2025-05-30-18-37-44
.. gh-issue: 134453
.. nonce: kxkA-o
.. section: Library

Fixed :func:`subprocess.Popen.communicate` ``input=`` handling of
:class:`memoryview` instances that were non-byte shaped on POSIX platforms.
Those are now properly cast to a byte shaped view instead of truncating the
input.  Windows platforms did not have this bug.

..

.. date: 2024-12-14-19-51-39
.. gh-issue: 127930
.. nonce: WsGnh9
.. section: Library

Add ``__all__`` to :mod:`tkinter.simpledialog`.

..

.. date: 2024-05-20-12-35-52
.. gh-issue: 115952
.. nonce: J6n_Kf
.. section: Library

Fix a potential memory denial of service in the :mod:`pickle` module. When
reading a pickled data received from untrusted source, it could cause an
arbitrary amount of memory to be allocated, even if the code that is allowed
to execute is restricted by overriding the
:meth:`~pickle.Unpickler.find_class` method. This could have led to symptoms
including a :exc:`MemoryError`, swapping, out of memory (OOM) killed
processes or containers, or even system crashes.

..

.. bpo: 40350
.. date: 2021-10-23-22-12-13
.. nonce: t0dQMY
.. section: Library

Fix support for namespace packages in :mod:`modulefinder`.

..

.. date: 2025-11-26-23-30-09
.. gh-issue: 141994
.. nonce: arBEG6
.. section: Documentation

:mod:`xml.sax.handler`: Make Documentation of
:data:`xml.sax.handler.feature_external_ges` warn of opening up to `external
entity attacks <https://en.wikipedia.org/wiki/XML_external_entity_attack>`_.
Patch by Sebastian Pipping.

..

.. date: 2025-12-16-01-17-21
.. gh-issue: 134584
.. nonce: tsxYYw
.. section: Core and Builtins

Eliminate redundant refcounting from ``_STORE_ATTR_INSTANCE_VALUE``.

..

.. date: 2025-12-15-15-07-40
.. gh-issue: 142718
.. nonce: zjiGjS
.. section: Core and Builtins

JIT: Fix segfault caused by not flushing the stack to memory at side exits.

..

.. date: 2025-12-15-15-01-21
.. gh-issue: 142737
.. nonce: xYXzeB
.. section: Core and Builtins

Tracebacks will be displayed in fallback mode even if :func:`io.open` is
lost. Previously, this would crash the interpreter. Patch by Bartosz
Sławecki.

..

.. date: 2025-12-15-03-20-24
.. gh-issue: 116738
.. nonce: NNHiTK
.. section: Core and Builtins

Make the attributes in :mod:`bz2` thread-safe on the :term:`free threaded
<free threading>` build.

..

.. date: 2025-12-14-21-46-07
.. gh-issue: 134584
.. nonce: vyec2h
.. section: Core and Builtins

Eliminate redundant refcounting from ``_CALL_LIST_APPEND``.

..

.. date: 2025-12-13-17-20-38
.. gh-issue: 142554
.. nonce: wNtEFF
.. section: Core and Builtins

Fix a crash in :func:`divmod` when :func:`!_pylong.int_divmod` does not
return a tuple of length two exactly. Patch by Bénédikt Tran.

..

.. date: 2025-12-10-23-03-10
.. gh-issue: 142531
.. nonce: NUEa1T
.. section: Core and Builtins

Fix a free-threaded GC performance regression.  If there are many untracked
tuples, the GC will run too often, resulting in poor performance.  The fix
is to include untracked tuples in the "long lived" object count. The number
of frozen objects is also now included since the free-threaded GC must scan
those too.

..

.. date: 2025-12-08-17-34-57
.. gh-issue: 142402
.. nonce: iV0ON3
.. section: Core and Builtins

Fix reference counting when adjacent literal parts are merged while
constructing :class:`string.templatelib.Template`, preventing the displaced
string object from leaking.

..

.. date: 2025-12-08-14-14-40
.. gh-issue: 116738
.. nonce: x7aaBF
.. section: Core and Builtins

Make the attributes in :mod:`zlib` thread-safe on the :term:`free threaded
<free threading>` build.

..

.. date: 2025-12-08-13-04-37
.. gh-issue: 142343
.. nonce: BTAyML
.. section: Core and Builtins

Fix SIGILL crash on m68k due to incorrect assembly constraint.

..

.. date: 2025-12-06-00-38-37
.. gh-issue: 142236
.. nonce: m3EF9E
.. section: Core and Builtins

Improve the "Perhaps you forgot a comma?" syntax error for multi-line string
concatenations to point to the last string instead of the first, making it
easier to locate where the comma is missing. Patch by Pablo Galindo.

..

.. date: 2025-12-06-00-16-43
.. gh-issue: 142236
.. nonce: m3EF9E
.. section: Core and Builtins

Fix incorrect keyword suggestions for syntax errors in :mod:`traceback`. The
keyword typo suggestion mechanism would incorrectly suggest replacements
when the extracted source code was incomplete rather than containing an
actual typo. Patch by Pablo Galindo.

..

.. date: 2025-12-05-17-24-34
.. gh-issue: 142305
.. nonce: ybXvtr
.. section: Core and Builtins

Decrease the size of the generated stencils and the runtime JIT code. Patch
by Diego Russo.

..

.. date: 2025-12-05-15-59-03
.. gh-issue: 135379
.. nonce: lDXbKO
.. section: Core and Builtins

Implement a limited form of register allocation known as "top of stack
caching" in the JIT. It works by keeping 0-3 of the top items in the stack
in registers. The code generator generates multiple versions of those uops
that do not escape and are relatively small. During JIT compilation, the
copy that produces the least memory traffic is selected, spilling or
reloading values when needed.

..

.. date: 2025-12-05-14-33-54
.. gh-issue: 142276
.. nonce: H4j8hP
.. section: Core and Builtins

Fix missing type watcher when promoting attribute loads to constants in the
JIT. Patch by Ken Jin. Reproducer by Yuancheng Jiang.

..

.. date: 2025-12-03-11-03-35
.. gh-issue: 142218
.. nonce: 44Fq_J
.. section: Core and Builtins

Fix crash when inserting into a split table dictionary with a non
:class:`str` key that matches an existing key.

..

.. date: 2025-12-02-21-11-46
.. gh-issue: 141976
.. nonce: yu7pDV
.. section: Core and Builtins

Check against abstract stack overflow in the JIT optimizer.

..

.. date: 2025-12-02-15-39-16
.. gh-issue: 97850
.. nonce: H6QKwl
.. section: Core and Builtins

Remove all ``*.load_module()`` usage and definitions from the import system
and importlib. The method has been deprecated in favor of
``importlib.abc.Loader.exec_module()`` since Python 3.4.

..

.. date: 2025-12-01-20-41-26
.. gh-issue: 142048
.. nonce: c2YosX
.. section: Core and Builtins

Fix quadratically increasing garbage collection delays in free-threaded
build.

..

.. date: 2025-12-01-15-22-54
.. gh-issue: 65961
.. nonce: hCJvRB
.. section: Core and Builtins

Stop setting ``__cached__`` on modules.

..

.. date: 2025-11-29-18-14-28
.. gh-issue: 141770
.. nonce: JURnvg
.. section: Core and Builtins

Annotate anonymous mmap usage only when supported by the Linux kernel and if
``-X dev`` is used or Python is built in debug mode. Patch by Donghee Na.

..

.. date: 2025-11-29-08-51-56
.. gh-issue: 142029
.. nonce: rUpcmt
.. section: Core and Builtins

Raise :exc:`ModuleNotFoundError` instead of crashing when a nonexistent
module is used as a name in ``_imp.create_builtin()``.

..

.. date: 2025-11-28-16-45-07
.. gh-issue: 142029
.. nonce: JuXiKu
.. section: Core and Builtins

Raise :exc:`ValueError` instead of crashing when empty string is used as a
name in ``_imp.create_builtin()``.

..

.. date: 2025-11-26-20-01-07
.. gh-issue: 141976
.. nonce: K8NDmR
.. section: Core and Builtins

Protect against specialization failures in the tracing JIT compiler for
performance reasons.

..

.. date: 2025-11-25-02-23-31
.. gh-issue: 141861
.. nonce: QcMdcM
.. section: Core and Builtins

Fix invalid memory read in the ``ENTER_EXECUTOR`` instruction.

..

.. date: 2025-11-24-21-09-30
.. gh-issue: 141930
.. nonce: hIIzSd
.. section: Core and Builtins

When importing a module, use Python's regular file object to ensure that
writes to ``.pyc`` files are complete or an appropriate error is raised.

..

.. date: 2025-11-24-16-07-57
.. gh-issue: 138122
.. nonce: m3EF9E
.. section: Core and Builtins

Add incomplete sample detection to prevent corrupted profiling data. Each
thread state now contains an embedded base frame (sentinel at the bottom of
the frame stack) with owner type ``FRAME_OWNED_BY_INTERPRETER``. The
profiler validates that stack unwinding terminates at this sentinel frame.
Samples that fail to reach the base frame (due to race conditions, memory
corruption, or other errors) are now rejected rather than being included as
spurious data.

..

.. date: 2025-11-22-10-43-26
.. gh-issue: 120158
.. nonce: 41_rXd
.. section: Core and Builtins

Fix inconsistent state when enabling or disabling monitoring events too many
times.

..

.. date: 2025-11-20-22-09-22
.. gh-issue: 140638
.. nonce: f6btj0
.. section: Core and Builtins

Expose a ``"candidates"`` stat in :func:`gc.get_stats` and
:data:`gc.callbacks`.

..

.. date: 2025-11-20-13-18-57
.. gh-issue: 141780
.. nonce: xDrVNr
.. section: Core and Builtins

Fix :c:macro:`Py_mod_gil` with API added in :pep:`793`:
:c:func:`!PyModule_FromSlotsAndSpec` and ``PyModExport`` hooks

..

.. date: 2025-11-19-16-40-24
.. gh-issue: 141732
.. nonce: PTetqp
.. section: Core and Builtins

Ensure the :meth:`~object.__repr__` for :exc:`ExceptionGroup` and
:exc:`BaseExceptionGroup` does not change when the exception sequence that
was original passed in to its constructor is subsequently mutated.

..

.. date: 2025-11-18-07-45-37
.. gh-issue: 140638
.. nonce: i06qxD
.. section: Core and Builtins

Expose a ``"duration"`` stat in :func:`gc.get_stats` and
:data:`gc.callbacks`.

..

.. date: 2025-11-17-14-40-45
.. gh-issue: 139653
.. nonce: LzOy1M
.. section: Core and Builtins

Only raise a ``RecursionError`` or trigger a fatal error if the stack
pointer is both below the limit pointer *and* above the stack base. If
outside of these bounds assume that it is OK. This prevents false positives
when user-space threads swap stacks.

..

.. date: 2025-11-16-21-14-48
.. gh-issue: 41779
.. nonce: rXIj5h
.. section: Core and Builtins

Allowed defining the *__dict__* and *__weakref__* :ref:`__slots__ <slots>`
for any class.

..

.. date: 2025-11-15-23-58-23
.. gh-issue: 139103
.. nonce: 9cVYJ0
.. section: Core and Builtins

Improve multithreaded scaling of dataclasses on the free-threaded build.

..

.. date: 2025-11-15-14-04-35
.. gh-issue: 141589
.. nonce: VfdMDD
.. section: Core and Builtins

Change ``backoff counter`` to use prime numbers instead of powers of 2. Use
only 3 bits for ``counter`` and 13 bits for ``value``. This allows to
support values up to 8191. Patch by Mikhail Efimov.

..

.. date: 2025-07-22-16-20-06
.. gh-issue: 137007
.. nonce: 1oPvvK
.. section: Core and Builtins

Fix a bug during JIT compilation failure which caused garbage collection
debug assertions to fail.

..

.. date: 2025-07-11-19-57-27
.. gh-issue: 132657
.. nonce: vwDuO2
.. section: Core and Builtins

For the free-threaded build, avoid locking the :class:`set` object for the
``__contains__`` method.

..

.. date: 2025-06-28-17-54-27
.. gh-issue: 134584
.. nonce: EXgPub
.. section: Core and Builtins

Eliminate redundant refcounting from ``_CALL_STR_1``.

..

.. date: 2025-06-28-04-32-38
.. gh-issue: 134584
.. nonce: eZogqn
.. section: Core and Builtins

Eliminate redundant refcounting from ``_CALL_BUILTIN_O``.

..

.. date: 2025-06-23-22-52-20
.. gh-issue: 134584
.. nonce: qbiQfG
.. section: Core and Builtins

Eliminate redundant refcounting from ``_CALL_TUPLE_1``. Patch by Noam Cohen

..

.. date: 2025-12-11-13-01-49
.. gh-issue: 142589
.. nonce: nNAqgw
.. section: C API

Fix :c:func:`PyUnstable_Object_IsUniqueReferencedTemporary()` handling of
tagged ints on the interpreter stack.

..

.. date: 2025-12-11-09-06-36
.. gh-issue: 142571
.. nonce: Csdxnn
.. section: C API

:c:func:`!PyUnstable_CopyPerfMapFile` now checks that opening the file
succeeded before flushing.

..

.. date: 2025-12-03-16-35-24
.. gh-issue: 142225
.. nonce: vmCJoo
.. section: C API

Fixed the :c:macro:`PyABIInfo_VAR` macro.

..

.. date: 2025-12-03-14-41-07
.. gh-issue: 141049
.. nonce: VuAUe2
.. section: C API

:c:func:`!_PyObject_CallMethodId`, :c:func:`!_PyObject_GetAttrId` and
:c:func:`!_PyUnicode_FromId` are deprecated since 3.15 and will be removed
in 3.20. Instead, use :c:func:`PyUnicode_InternFromString()` and cache the
result in the module state, then call :c:func:`PyObject_CallMethod` or
:c:func:`PyObject_GetAttr`. Patch by Victor Stinner.

..

.. date: 2025-12-01-18-17-16
.. gh-issue: 142163
.. nonce: 2HiX5A
.. section: C API

Fix the ``HAVE_THREAD_LOCAL`` macro being defined without the
``Py_BUILD_CORE`` macro set after including :file:`Python.h`.

..

.. date: 2025-11-21-10-34-00
.. gh-issue: 137422
.. nonce: tzZKLi
.. section: C API

Fix :term:`free threading` race condition in
:c:func:`PyImport_AddModuleRef`. It was previously possible for two calls to
the function return two different objects, only one of which was stored in
:data:`sys.modules`.

..

.. date: 2025-11-18-18-36-15
.. gh-issue: 141726
.. nonce: ILrhyK
.. section: C API

Add :c:func:`PyDict_SetDefaultRef` to the Stable ABI.

..

.. date: 2025-11-18-04-16-09
.. gh-issue: 140042
.. nonce: S1C7id
.. section: C API

Removed the sqlite3_shutdown call that could cause closing connections for
sqlite when used with multiple sub interpreters.

..

.. date: 2025-11-05-21-48-31
.. gh-issue: 141070
.. nonce: mkrhjQ
.. section: C API

Add :c:func:`PyUnstable_Object_Dump` to dump an object to ``stderr``. It
should only be used for debugging. Patch by Victor Stinner.

..

.. date: 2025-09-22-16-32-00
.. gh-issue: 139165
.. nonce: 6Czn7S
.. section: C API

Expose the functions :c:func:`Py_SIZE`, :c:func:`Py_IS_TYPE` and
:c:func:`Py_SET_SIZE` in the Stable ABI.

..

.. date: 2025-12-09-14-23-51
.. gh-issue: 131372
.. nonce: 2TAEyz
.. section: Build

Add ``LDVERSION`` and ``EXE`` to the ``base_interpreter`` value of
``build-details.json``.

..

.. date: 2025-12-09-13-33-46
.. gh-issue: 142454
.. nonce: cqUxzQ
.. section: Build

When calculating the digest of the JIT stencils input, sort the hashed files
by filenames before adding their content to the hasher. This ensures
deterministic hash input and hence deterministic hash, independent on
filesystem order.

..

.. date: 2025-12-04-20-57-15
.. gh-issue: 131372
.. nonce: o397g7
.. section: Build

``build-details.py`` will only be installed as part of the main install
(``make install``). ``make altinstall`` will no longer include it.

..

.. date: 2025-12-03-10-44-42
.. gh-issue: 142234
.. nonce: i1kaFb
.. section: Build

Allow ``--enable-wasm-dynamic-linking`` for WASI. While CPython doesn't
directly support it so external/downstream users do not have to patch in
support for the flag.

..

.. date: 2025-11-28-21-43-07
.. gh-issue: 142050
.. nonce: PFi4tv
.. section: Build

Fixed a bug where JIT stencils produced on Windows contained debug data.
Patch by Chris Eibl.

..

.. date: 2025-11-28-19-49-01
.. gh-issue: 141808
.. nonce: cV5K12
.. section: Build

Do not generate the jit stencils twice in case of PGO builds on Windows.

..

.. date: 2025-11-25-13-17-47
.. gh-issue: 141926
.. nonce: KmuM2h
.. section: Build

``RUNSHARED`` is no longer cleared when cross-compiling. Previously,
``RUNSHARED`` was cleared when cross-compiling, which breaks PGO when using
``--enabled-shared`` on systems where the cross-compiled CPython is
otherwise executable (e.g., via transparent emulation).

..

.. date: 2025-11-20-23-15-39
.. gh-issue: 141808
.. nonce: NEewZC
.. section: Build

When running ``make clean-retain-profile``, keep the generated JIT stencils.
That way, the stencils are not generated twice when Profile-guided
optimization (PGO) is used. It also allows distributors to supply their own
pre-built JIT stencils.

..

.. date: 2025-11-20-17-01-05
.. gh-issue: 141784
.. nonce: LkYI2n
.. section: Build

Fix ``_remote_debugging_module.c`` compilation on 32-bit Linux. Include
Python.h before system headers to make sure that
``_remote_debugging_module.c`` uses the same types (ABI) than Python. Patch
by Victor Stinner.

..

.. date: 2025-11-19-09-21-17
.. gh-issue: 141172
.. nonce: cYWc4x
.. section: Build

Update to WASI SDK 29.

..

.. date: 2025-10-30-10-36-15
.. gh-issue: 139707
.. nonce: QJ1FfJ
.. section: Build

Add configure option :option:`--with-missing-stdlib-config=FILE` allows
which distributors to pass a `JSON <https://www.json.org/json-en.html>`_
configuration file containing custom error messages for missing
:term:`standard library` modules.

..

.. date: 2025-04-29-18-25-34
.. gh-issue: 108819
.. nonce: qMUTRB
.. section: Build

Honor :option:`--with-platlibdir` in the pure-Python standard library
installation path, if ``PLATLIBDIR`` doesn't match the value used in
``LIBDIR``.