Misc/NEWS.d/3.15.0a4.rst

.. date: 2025-12-17-02-02-57
.. gh-issue: 142836
.. nonce: mR-fvK
.. release date: 2026-01-13
.. section: Tests

Accommodated Solaris in ``test_pdb.test_script_target_anonymous_pipe``.

..

.. date: 2025-12-22-22-36-21
.. gh-issue: 122431
.. nonce: 9E3085
.. section: Library

Corrected the error message in :func:`readline.append_history_file` to state
that ``nelements`` must be non-negative instead of positive.

..

.. date: 2025-12-21-17-44-28
.. gh-issue: 143046
.. nonce: GBa5Ip
.. section: Library

The :mod:`asyncio` REPL no longer prints copyright and version messages in
the quiet mode (:option:`-q`). Patch by Bartosz Sławecki.

..

.. date: 2025-12-20-16-35-42
.. gh-issue: 80744
.. nonce: X4pZ2N
.. section: Library

Fix issue where ``pdb`` would read a ``.pdbrc`` twice if launched from the
home directory

..

.. date: 2025-12-20-02-33-05
.. gh-issue: 138122
.. nonce: m3EF9E
.. section: Library

Add blocking mode to Tachyon for accurate stack traces in applications with
many generators or fast-changing call stacks. Patch by Pablo Galindo.

..

.. date: 2025-12-20-01-49-02
.. gh-issue: 143010
.. nonce: _-SWX0
.. section: Library

Fixed a bug in :mod:`mailbox` where the precise timing of an external event
could result in the library opening an existing file instead of a file it
expected to create.

..

.. date: 2025-12-17-14-41-09
.. gh-issue: 112127
.. nonce: 13OHQk
.. section: Library

Fix possible use-after-free in :func:`atexit.unregister` when the callback
is unregistered during comparison.

..

.. date: 2025-12-17-03-03-12
.. gh-issue: 138122
.. nonce: m3EF9E
.. section: Library

Fix incomplete stack traces in the Tachyon profiler's frame cache when
profiling code with deeply nested generators. The frame cache now validates
that stack traces reach the base frame before caching, preventing broken
flamegraphs. Patch by Pablo Galindo.

..

.. date: 2025-12-16-15-32-41
.. gh-issue: 142834
.. nonce: g7mHw_
.. section: Library

Change the :mod:`pdb` ``commands`` command to use the last available
breakpoint instead of failing when the most recently created breakpoint was
deleted.

..

.. date: 2025-12-16-14-49-19
.. gh-issue: 142783
.. nonce: VPV1ig
.. section: Library

Fix zoneinfo use-after-free with descriptor _weak_cache. a descriptor as
_weak_cache could cause crashes during object creation. The fix ensures
proper reference counting for descriptor-provided objects.

..

.. date: 2025-12-16-14-21-20
.. gh-issue: 76007
.. nonce: O4AmYl
.. section: Library

Deprecate ``VERSION`` from :mod:`xml.etree.ElementTree` and ``version`` from
:mod:`!xml.sax.expatreader` and :mod:`xml.sax.handler`. Patch by Hugo van
Kemenade.

..

.. date: 2025-12-16-04-39-27
.. gh-issue: 142784
.. nonce: HBGJag
.. section: Library

The :mod:`asyncio` REPL now properly closes the loop upon the end of
interactive session. Previously, it could cause surprising warnings.
Contributed by Bartosz Sławecki.

..

.. date: 2025-12-15-02-00-31
.. gh-issue: 138122
.. nonce: m3EF9E
.. section: Library

Add binary output format to :mod:`profiling.sampling` for compact storage of
profiling data. The new ``--binary`` option captures samples to a file that
can be converted to other formats using the ``replay`` command. Patch by
Pablo Galindo

..

.. date: 2025-12-13-23-26-42
.. gh-issue: 142495
.. nonce: I88Uv_
.. section: Library

:class:`collections.defaultdict` now prioritizes :meth:`~object.__setitem__`
when inserting default values from ``default_factory``. This prevents race
conditions where a default value would overwrite a value set before
``default_factory`` returns.

..

.. date: 2025-12-13-10-34-59
.. gh-issue: 142654
.. nonce: fmm974
.. section: Library

Show the clearer error message when using ``profiling.sampling`` on an
unknown PID.

..

.. date: 2025-12-11-22-59-33
.. gh-issue: 142560
.. nonce: GkJrkk
.. section: Library

Fix use-after-free in :class:`bytearray` search-like methods
(:meth:`~bytearray.find`, :meth:`~bytearray.count`,
:meth:`~bytearray.index`, :meth:`~bytearray.rindex`, and
:meth:`~bytearray.rfind`) by marking the storage as exported which causes
reallocation attempts to raise :exc:`BufferError`. For
:func:`~operator.contains`, :meth:`~bytearray.split`, and
:meth:`~bytearray.rsplit` the :ref:`buffer protocol <bufferobjects>` is used
for this.

..

.. date: 2025-12-10-02-31-43
.. gh-issue: 142419
.. nonce: C8_LES
.. section: Library

:meth:`mmap.mmap.set_name` method added to annotate an anonymous memory map
if Linux kernel supports ``PR_SET_VMA_ANON_NAME`` (Linux 5.17 or newer).
Patch by Donghee Na.

..

.. date: 2025-10-12-12-05-52
.. gh-issue: 139971
.. nonce: UdoStU
.. section: Library

:mod:`pydoc`: Ensure that the link to the online documentation of a
:term:`stdlib` module is correct.

..

.. date: 2025-07-20-15-39-54
.. gh-issue: 124098
.. nonce: znFPIp
.. section: Library

Fix issue where methods in handlers that lacked the protocol name but
matched a valid base handler method (e.g., ``_open()`` or ``error()``) were
incorrectly added to :class:`urllib.request.OpenerDirector`'s handlers.
Contributed by Andrea Mattei.

..

.. date: 2025-07-05-08-30-07
.. gh-issue: 136282
.. nonce: K3JKyD
.. section: Library

Add support for :const:`~configparser.UNNAMED_SECTION` when creating a
section via the mapping protocol access

..

.. date: 2025-12-22-12-03-09
.. gh-issue: 143057
.. nonce: Majsre
.. section: Core and Builtins

Avoid locking in :c:func:`PyTraceMalloc_Track` and
:c:func:`PyTraceMalloc_Untrack` when :mod:`tracemalloc` is not enabled.

..

.. date: 2025-12-21-00-25-26
.. gh-issue: 139109
.. nonce: gwSsOL
.. section: Core and Builtins

Add missing terminator in certain cases when tracing in the new JIT
compiler.

..

.. date: 2025-12-19-00-59-29
.. gh-issue: 142961
.. nonce: q8WRSq
.. section: Core and Builtins

Fix a segfault in the JIT when constant folding ``len(tuple)``.

..

.. date: 2025-12-18-01-00-14
.. gh-issue: 142776
.. nonce: ACaoeP
.. section: Core and Builtins

Fix a file descriptor leak in import.c

..

.. date: 2025-12-17-20-31-09
.. gh-issue: 139757
.. nonce: 6DWxeQ
.. section: Core and Builtins

Fix building JIT stencils on free-threaded builds.

..

.. date: 2025-12-17-10-49-03
.. gh-issue: 129068
.. nonce: GlYnrO
.. section: Core and Builtins

Make concurrent iteration over the same range iterator thread-safe in the
free threading build.

..

.. date: 2025-12-16-23-26-41
.. gh-issue: 142543
.. nonce: wJKjBs
.. section: Core and Builtins

Fix a stack overflow on Clang JIT build configurations with full LTO.

..

.. date: 2025-12-16-20-38-17
.. gh-issue: 142448
.. nonce: mAFqwL
.. section: Core and Builtins

Fix a bug when using monitoring with the JIT.

..

.. date: 2025-12-16-11-56-20
.. gh-issue: 142766
.. nonce: Uy2HTm
.. section: Core and Builtins

Clear the frame of a generator when :meth:`generator.close` is called.

..

.. date: 2025-12-16-05-52-37
.. gh-issue: 134584
.. nonce: VsfOQR
.. section: Core and Builtins

Eliminate redundant refcounting from ``_LOAD_ATTR_INSTANCE_VALUE``.

..

.. date: 2025-12-16-05-24-24
.. gh-issue: 134584
.. nonce: tJ1usH
.. section: Core and Builtins

Eliminate redundant refcounting from ``_STORE_ATTR_WITH_HINT``.

..

.. date: 2025-12-13-01-11-03
.. gh-issue: 142476
.. nonce: 44Sp4N
.. section: Core and Builtins

Fix a memory leak in the experimental Tier 2 optimizer when creating
executors. Patched by Shamil Abdulaev.

..

.. date: 2025-11-06-05-21-25
.. gh-issue: 100964
.. nonce: TxPf1b
.. section: Core and Builtins

Fix reference cycle in exhausted generator frames. Patch by Savannah
Ostrowski.

..

.. date: 2025-10-11-17-01-21
.. gh-issue: 139922
.. nonce: RUkXyd
.. section: Core and Builtins

Allow building CPython with the tail calling interpreter on Visual Studio
2026 MSVC. This provides a performance gain over the prior interpreter for
MSVC. Patch by Ken Jin, Brandt Bucher, and Chris Eibl. With help from the
MSVC team including Hulon Jenkins.