cpython/Misc/NEWS.d/3.15.0a8.rst

.. date: 2026-03-14-17-31-39
.. gh-issue: 145986
.. nonce: ifSSr8
.. release date: 2026-04-07
.. section: Security

:mod:`xml.parsers.expat`: Fixed a crash caused by unbounded C recursion when
converting deeply nested XML content models with
:meth:`~xml.parsers.expat.xmlparser.ElementDeclHandler`. This addresses
:cve:`2026-4224`.

..

.. date: 2026-03-06-17-03-38
.. gh-issue: 145599
.. nonce: kchwZV
.. section: Security

Reject control characters in :class:`http.cookies.Morsel`
:meth:`~http.cookies.Morsel.update` and
:meth:`~http.cookies.BaseCookie.js_output`. This addresses :cve:`2026-3644`.

..

.. date: 2026-01-16-12-04-49
.. gh-issue: 143930
.. nonce: zYC5x3
.. section: Security

Reject leading dashes in URLs passed to :func:`webbrowser.open`.

..

.. date: 2026-04-06-11-15-46
.. gh-issue: 148157
.. nonce: JFnZDn
.. section: Core and Builtins

Fix an unlikely crash when parsing an invalid type comments for function
parameters. Found by OSS Fuzz in :oss-fuzz:`492782951`.

..

.. date: 2026-04-06-00-00-00
.. gh-issue: 100239
.. nonce: binopxt
.. section: Core and Builtins

Propagate result type and uniqueness information through
``_BINARY_OP_EXTEND`` in the tier 2 optimizer, enabling elimination of
downstream type guards and selection of inplace float operations.

..

.. date: 2026-04-05-15-20-00
.. gh-issue: 148144
.. nonce: f7qA0x
.. section: Core and Builtins

Initialize ``_PyInterpreterFrame.visited`` when copying interpreter frames
so incremental GC does not read an uninitialized byte from generator and
frame-object copies.

..

.. date: 2026-04-05-00-00-00
.. gh-issue: 148072
.. nonce: xid9Pe
.. section: Core and Builtins

Cache ``pickle.dumps`` and ``pickle.loads`` per interpreter in the XIData
framework, avoiding repeated module lookups on every cross-interpreter data
transfer.  This speeds up
:class:`~concurrent.futures.InterpreterPoolExecutor` for mutable types
(``list``, ``dict``) by 1.7x--3.3x.

..

.. date: 2026-04-04-22-20-00
.. gh-issue: 148110
.. nonce: cL5x2Q
.. section: Core and Builtins

Fix :func:`sys.set_lazy_imports_filter` so relative lazy imports pass the
resolved imported module name to the filter callback. Patch by Pablo
Galindo.

..

.. date: 2026-04-04-20-59-12
.. gh-issue: 148083
.. nonce: 9ZHNBN
.. section: Core and Builtins

Constant-fold ``_CONTAINS_OP_SET`` for :class:`frozenset`. Patch by Donghee
Na.

..

.. date: 2026-04-01-12-52-31
.. gh-issue: 144319
.. nonce: iZk4hs
.. section: Core and Builtins

Fix a bug that could cause applications with specific allocation patterns to
leak memory via Huge Pages if compiled with Huge Page support. Patch by
Pablo Galindo

..

.. date: 2026-04-01-12-35-55
.. gh-issue: 147985
.. nonce: YVirHJ
.. section: Core and Builtins

Make :c:func:`PySet_Contains` attempt a lock-free lookup, similar to
:meth:`!set.__contains__`.  This avoids acquiring the set object mutex in
the normal case.

..

.. date: 2026-03-31-18-07-53
.. gh-issue: 147856
.. nonce: 62Dwee
.. section: Core and Builtins

Allow the *count* argument of :meth:`bytes.replace` to be a keyword.

..

.. date: 2026-03-31-01-06-35
.. gh-issue: 146615
.. nonce: fix-method-get
.. section: Core and Builtins

Fix a crash in :meth:`~object.__get__` for :c:expr:`METH_METHOD` descriptors
when an invalid (non-type) object is passed as the second argument. Patch by
Steven Sun.

..

.. date: 2026-03-30-20-00-00
.. gh-issue: 146306
.. nonce: C45609
.. section: Core and Builtins

Optimize compact integer arithmetic in the JIT by mutating
uniquely-referenced operands in place, avoiding allocation of a new int
object. Speeds up the pyperformance ``spectral_norm`` benchmark by ~10%.

..

.. date: 2026-03-29-11-39-05
.. gh-issue: 146587
.. nonce: YJicXt
.. section: Core and Builtins

Fix type slot assignment incase of multiple slots for same name in type
object implementation. Patch by Kumar Aditya.

..

.. date: 2026-03-27-17-14-18
.. gh-issue: 126910
.. nonce: hooVFQ
.. section: Core and Builtins

Set frame pointers in ``aarch64-unknown-linux-gnu`` JIT code, allowing most
native profilers and debuggers to unwind through them. Patch by Diego Russo

..

.. date: 2026-03-26-11-18-45
.. gh-issue: 146388
.. nonce: O0u1c3
.. section: Core and Builtins

Adds a null check to handle when the JIT optimizer runs out of space when
dealing with contradictions in ``make_bottom``.

..

.. date: 2026-03-24-13-06-52
.. gh-issue: 146369
.. nonce: 6wDI6S
.. section: Core and Builtins

Ensure ``-X lazy_imports=none``` and ``PYTHON_LAZY_IMPORTS=none``` override
``__lazy_modules__``. Patch by Hugo van Kemenade.

..

.. date: 2026-03-22-19-30-00
.. gh-issue: 146308
.. nonce: AxnRVA
.. section: Core and Builtins

Fixed multiple error handling issues in the :mod:`!_remote_debugging` module
including a double-free in code object caching, memory leaks on allocation
failure, missing exception checks in binary format varint decoding,
reference leaks on error paths in frame chain processing, and inconsistent
thread status error reporting across platforms. Patch by Pablo Galindo.

..

.. date: 2026-03-22-12-00-00
.. gh-issue: 146306
.. nonce: 870ef4
.. section: Core and Builtins

Optimize float arithmetic in the JIT by mutating uniquely-referenced
operands in place, avoiding allocation of a new float object. Speeds up the
pyperformance ``nbody`` benchmark by ~19%.

..

.. date: 2026-03-21-15-05-14
.. gh-issue: 146128
.. nonce: DG1Hfa
.. section: Core and Builtins

Fix a bug which could cause constant values to be partially corrupted in
AArch64 JIT code. This issue is theoretical, and hasn't actually been
observed in unmodified Python interpreters.

..

.. date: 2026-03-21-11-55-16
.. gh-issue: 146250
.. nonce: ahl3O2
.. section: Core and Builtins

Fixed a memory leak in :exc:`SyntaxError` when re-initializing it.

..

.. date: 2026-03-21-08-48-25
.. gh-issue: 146245
.. nonce: cqM3_4
.. section: Core and Builtins

Fixed reference leaks in :mod:`socket` when audit hooks raise exceptions in
:func:`socket.getaddrinfo` and :meth:`!socket.sendto`.

..

.. date: 2026-03-21-08-11-58
.. gh-issue: 146151
.. nonce: 4-lhim
.. section: Core and Builtins

:class:`memoryview` now supports the :c:expr:`float complex` and
:c:expr:`double complex` C types: formatting characters ``'F'`` and ``'D'``
respectively.  Patch by Sergey B Kirpichev.

..

.. date: 2026-03-20-13-55-14
.. gh-issue: 146196
.. nonce: Zg70Kb
.. section: Core and Builtins

Fix potential Undefined Behavior in :c:func:`PyUnicodeWriter_WriteASCII` by
adding a zero-length check. Patch by Shamil Abdulaev.

..

.. date: 2026-03-20-13-07-33
.. gh-issue: 146227
.. nonce: MqBPEo
.. section: Core and Builtins

Fix wrong type in ``_Py_atomic_load_uint16`` in the C11 atomics backend
(``pyatomic_std.h``), which used a 32-bit atomic load instead of 16-bit.
Found by Mohammed Zuhaib.

..

.. date: 2026-03-20-12-52-55
.. gh-issue: 146205
.. nonce: M4yKdf
.. section: Core and Builtins

Fixed a bug where :meth:`select.epoll.close`, :meth:`select.kqueue.close`,
and :meth:`select.devpoll.close` silently ignored errors.

..

.. date: 2026-03-20-12-26-24
.. gh-issue: 146199
.. nonce: vV8V9s
.. section: Core and Builtins

Comparison of code objects now handles errors correctly.

..

.. date: 2026-03-20-11-34-17
.. gh-issue: 145667
.. nonce: _Agp9o
.. section: Core and Builtins

Remove the ``GET_ITER_YIELD_FROM`` instruction, modifying ``SEND`` to pair
with ``GET_ITER`` when compiling ``yield from`` expressions.

..

.. date: 2026-03-20-00-39-25
.. gh-issue: 146192
.. nonce: 8aQ6sC
.. section: Core and Builtins

Add Base32 support to :mod:`binascii` and improve the performance of the
Base32 converters in :mod:`base64`. Patch by James Seo.

..

.. date: 2026-03-19-16-16-40
.. gh-issue: 135871
.. nonce: jSExZ3
.. section: Core and Builtins

Improve multithreaded scaling of PyMutex in low-contention scenarios by
reloading the lock's internal state, without slowing down high-contention
scenarios.

..

.. date: 2026-03-19-01-19-34
.. gh-issue: 146096
.. nonce: R9tkJX
.. section: Core and Builtins

Fixed segmentation fault when called repr for BaseExceptionGroup with empty
or 1-size tuple args.

..

.. date: 2026-03-18-18-52-00
.. gh-issue: 146056
.. nonce: r1tVSo
.. section: Core and Builtins

Fix :func:`repr` for lists and tuples containing ``NULL``\ s.

..

.. date: 2026-03-17-14-20-56
.. gh-issue: 145059
.. nonce: aB3xKm
.. section: Core and Builtins

Fixed ``sys.lazy_modules`` to include lazy modules without submodules. Patch
by Bartosz Sławecki.

..

.. date: 2026-03-17-00-00-00
.. gh-issue: 146041
.. nonce: 7799bb
.. section: Core and Builtins

Fix free-threading scaling bottleneck in :func:`sys.intern` and
:c:func:`PyObject_SetAttr` by avoiding the interpreter-wide lock when the
string is already interned and immortalized.

..

.. date: 2026-03-15-21-45-35
.. gh-issue: 145990
.. nonce: tmXwRB
.. section: Core and Builtins

``python --help-env`` sections are now sorted by environment variable name.

..

.. date: 2026-03-15-20-47-34
.. gh-issue: 145990
.. nonce: 14BUzw
.. section: Core and Builtins

``python --help-xoptions`` is now sorted by ``-X`` option name.

..

.. date: 2026-03-13-12-24-17
.. gh-issue: 145876
.. nonce: LWFO2K
.. section: Core and Builtins

:exc:`AttributeError`\ s and :exc:`KeyError`\ s raised in :meth:`!keys` or
:meth:`!__getitem__` during dictionary unpacking (``{**mymapping}`` or
``func(**mymapping)``) are no longer masked by :exc:`TypeError`.

..

.. date: 2026-03-13-09-48-57
.. gh-issue: 127958
.. nonce: U-znTv
.. section: Core and Builtins

Support tracing from function entrypoints in the JIT. Patch by Ken Jin.

..

.. date: 2026-03-11-21-27-28
.. gh-issue: 145376
.. nonce: LfDvyw
.. section: Core and Builtins

Fix GC tracking in ``structseq.__replace__()``.

..

.. date: 2026-03-11-19-09-47
.. gh-issue: 145792
.. nonce: X5KUhc
.. section: Core and Builtins

Fix out-of-bounds access when invoking faulthandler on a CPython build
compiled without support for VLAs.

..

.. date: 2026-03-11-00-13-59
.. gh-issue: 142183
.. nonce: 2iVhJH
.. section: Core and Builtins

Avoid a pathological case where repeated calls at a specific stack depth
could be significantly slower.

..

.. date: 2026-03-10-22-38-40
.. gh-issue: 145779
.. nonce: 5375381d80
.. section: Core and Builtins

Improve scaling of :func:`classmethod` and :func:`staticmethod` calls in the
free-threaded build by avoiding the descriptor ``__get__`` call.

..

.. date: 2026-03-10-19-00-39
.. gh-issue: 145783
.. nonce: dS5TM9
.. section: Core and Builtins

Fix an unlikely crash in the parser when certain errors were erroneously not
propagated. Found by OSS Fuzz in :oss-fuzz:`491369109`.

..

.. date: 2026-03-10-12-52-06
.. gh-issue: 145685
.. nonce: 80B7gK
.. section: Core and Builtins

Improve scaling of type attribute lookups in the :term:`free-threaded build`
by avoiding contention on the internal type lock.

..

.. date: 2026-03-09-00-00-00
.. gh-issue: 145713
.. nonce: KR6azvzI
.. section: Core and Builtins

Make :meth:`bytearray.resize` thread-safe in the free-threaded build by
using a critical section and calling the lock-held variant of the resize
function.

..

.. date: 2026-02-28-18-42-36
.. gh-issue: 145036
.. nonce: 70Kbfz
.. section: Core and Builtins

In free-threaded build, fix race condition when calling :meth:`!__sizeof__`
on a :class:`list`

..

.. date: 2026-02-14-15-51-16
.. gh-issue: 134584
.. nonce: 6WFSuB
.. section: Core and Builtins

Eliminate redundant refcounting for ``MATCH_CLASS`` in the JIT.

..

.. date: 2026-02-14-13-07-08
.. gh-issue: 69605
.. nonce: 4aL4hn
.. section: Core and Builtins

Add :mod:`math.integer` to :term:`REPL` auto-completion of imports.

..

.. date: 2026-02-08-01-19-50
.. gh-issue: 131798
.. nonce: PaWDNH
.. section: Core and Builtins

Optimize ``_ITER_CHECK_RANGE`` and ``_ITER_CHECK_LIST`` in the JIT

..

.. date: 2026-01-31-15-15-43
.. gh-issue: 143414
.. nonce: Jgl4xu
.. section: Core and Builtins

Add tracking to the JIT optimizer to determine whether a reference is
uniquely owned or shared

..

.. date: 2026-01-10-12-59-58
.. gh-issue: 143636
.. nonce: dzr26e
.. section: Core and Builtins

Fix a crash when calling :class:`SimpleNamespace.__replace__()
<types.SimpleNamespace>` on non-namespace instances. Patch by Bénédikt Tran.

..

.. date: 2026-01-07-23-07-17
.. gh-issue: 126910
.. nonce: d8zdm-
.. section: Core and Builtins

Set frame pointers in ``x86_64-unknown-linux-gnu`` JIT code, allowing most
native profilers and debuggers to unwind through them.

..

.. date: 2025-11-02-16-23-17
.. gh-issue: 140594
.. nonce: YIWUpl
.. section: Core and Builtins

Fix an out of bounds read when a single NUL character is read from the
standard input. Patch by Shamil Abdulaev.

..

.. date: 2025-11-01-01-49-52
.. gh-issue: 140870
.. nonce: iknc12
.. section: Core and Builtins

Add support for module attributes in the :term:`REPL` auto-completion of
imports.

..

.. date: 2026-04-07-01-04-00
.. gh-issue: 144503
.. nonce: argvfs
.. section: Library

Fix a regression introduced in 3.14.3 and 3.13.12 where the
:mod:`multiprocessing` ``forkserver`` start method would fail with
:exc:`BrokenPipeError` when the parent process had a very large
:data:`sys.argv`.  The argv is now passed to the forkserver as separate
command-line arguments rather than being embedded in the ``-c`` command
string, avoiding the operating system's per-argument length limit.

..

.. date: 2026-04-06-11-20-24
.. gh-issue: 148153
.. nonce: ZtsuTl
.. section: Library

:func:`base64.b32encode` now always raises :exc:`ValueError` instead of
:exc:`AssertionError` for the value of *map01* with invalid length.

..

.. date: 2026-04-01-18-17-55
.. gh-issue: 73613
.. nonce: PLEebm
.. section: Library

Add the *padded* parameter in functions related to Base32 and Base64 codecs
in the :mod:`binascii` and :mod:`base64` modules. In the encoding functions
it controls  whether the pad character can be added in the output, in the
decoding functions it controls whether padding is required in input. Padding
of input no longer required in :func:`base64.urlsafe_b64decode` by default.

..

.. date: 2026-04-01-11-05-36
.. gh-issue: 146613
.. nonce: GzjUFK
.. section: Library

:mod:`itertools`: Fix a crash in :func:`itertools.groupby` when the grouper
iterator is concurrently mutated.

..

.. date: 2026-03-31-19-54-32
.. gh-issue: 147944
.. nonce: 3dn8GZ
.. section: Library

Accepted range for the *bytes_per_sep* argument of :meth:`bytes.hex`,
:meth:`bytearray.hex`, :meth:`memoryview.hex`, and :func:`binascii.b2a_hex`
is now increased, so passing ``sys.maxsize`` and ``-sys.maxsize`` is now
valid.

..

.. date: 2026-03-28-13-19-20
.. gh-issue: 146080
.. nonce: srN12a
.. section: Library

:mod:`ssl`: fix a crash when an SNI callback tries to use an SSL object that
has already been garbage-collected. Patch by Bénédikt Tran.

..

.. date: 2026-03-28-12-20-19
.. gh-issue: 146556
.. nonce: Y8Eson
.. section: Library

Fix :func:`annotationlib.get_annotations` hanging indefinitely when called
with ``eval_str=True`` on a callable that has a circular ``__wrapped__``
chain (e.g. ``f.__wrapped__ = f``). Cycle detection using an id-based
visited set now stops the traversal and falls back to the globals found so
far, mirroring the approach of :func:`inspect.unwrap`.

..

.. date: 2026-03-28-12-05-34
.. gh-issue: 146090
.. nonce: wf9_ef
.. section: Library

:mod:`sqlite3`: fix a crash when :meth:`sqlite3.Connection.create_collation`
fails with `SQLITE_BUSY <https://sqlite.org/rescode.html#busy>`__. Patch by
Bénédikt Tran.

..

.. date: 2026-03-28-12-01-48
.. gh-issue: 146090
.. nonce: wh1qJR
.. section: Library

:mod:`sqlite3`: properly raise :exc:`MemoryError` instead of
:exc:`SystemError` when a context callback fails to be allocated. Patch by
Bénédikt Tran.

..

.. date: 2026-03-27-12-00-00
.. gh-issue: 146507
.. nonce: 1D95A7
.. section: Library

Make :meth:`asyncio.SelectorEventLoop` stream transport's
:meth:`~asyncio.WriteTransport.get_write_buffer_size` O(1) by maintaining a
running byte counter instead of iterating the buffer on every call.

..

.. date: 2026-03-26-14-51-55
.. gh-issue: 145056
.. nonce: QS-6l1
.. section: Library

Fix merging of :class:`collections.OrderedDict` and :class:`frozendict`.

..

.. date: 2026-03-26-14-44-07
.. gh-issue: 145056
.. nonce: L9KPC3
.. section: Library

Add support for merging :class:`collections.UserDict` and
:class:`frozendict`.

..

.. date: 2026-03-26-11-04-42
.. gh-issue: 145633
.. nonce: RWjlaX
.. section: Library

Fix ``struct.pack('f', float)``: use :c:func:`PyFloat_Pack4` to raise
:exc:`OverflowError`. Patch by Sergey B Kirpichev and Victor Stinner.

..

.. date: 2026-03-26-02-06-52
.. gh-issue: 146440
.. nonce: HXjhQO
.. section: Library

:mod:`json`: Add the *array_hook* parameter to  :func:`~json.load` and
:func:`~json.loads` functions: allow a callback for JSON literal array types
to customize Python lists in the resulting decoded object. Passing combined
:class:`frozendict` to *object_pairs_hook* param and :class:`tuple` to
``array_hook`` will yield a deeply nested immutable Python structure
representing the JSON data.

..

.. date: 2026-03-25-21-08-51
.. gh-issue: 146431
.. nonce: zERPwe
.. section: Library

Add the *wrapcol* parameter to :mod:`base64` functions
:func:`~base64.b16encode`, :func:`~base64.b32encode`,
:func:`~base64.b32hexencode`, :func:`~base64.b85encode` and
:func:`~base64.z85encode`, and :mod:`binascii` functions
:func:`~binascii.b2a_base32` and :func:`~binascii.b2a_base85`. Add the
*ignorechars* parameter to :mod:`base64` functions
:func:`~base64.b16decode`, :func:`~base64.b32decode`,
:func:`~base64.b32hexdecode`, :func:`~base64.b85decode` and
:func:`~base64.z85decode`, and :mod:`binascii` functions
:func:`~binascii.a2b_hex`, :func:`~binascii.unhexlify`,
:func:`~binascii.a2b_base32` and :func:`~binascii.a2b_base85`.

..

.. date: 2026-03-24-03-49-50
.. gh-issue: 146310
.. nonce: WhlDir
.. section: Library

The :mod:`ensurepip` module no longer looks for ``pip-*.whl`` wheel packages
in the current directory.

..

.. date: 2026-03-21-16-03-16
.. gh-issue: 141510
.. nonce: tKptA7
.. section: Library

Support :class:`frozendict` in :mod:`plistlib`, for serialization only.
Patch by Hugo van Kemenade.

..

.. date: 2026-03-21-10-02-20
.. gh-issue: 146238
.. nonce: 2WpMOj
.. section: Library

Support half-floats (type code ``'e'`` of the :mod:`struct` module) in the
:mod:`array` module.  Patch by Sergey B Kirpichev.

..

.. date: 2026-03-21-08-23-26
.. gh-issue: 140947
.. nonce: owZ4r_
.. section: Library

Fix incorrect contextvars handling in server tasks created by
:mod:`asyncio`. Patch by Kumar Aditya.

..

.. date: 2026-03-21-06-21-38
.. gh-issue: 146151
.. nonce: yNpgml
.. section: Library

Support the :c:expr:`float complex` and :c:expr:`double complex` C types in
the :mod:`array` module: formatting characters ``'F'`` and ``'D'``
respectively.  Patch by Sergey B Kirpichev.

..

.. date: 2026-03-20-16-17-31
.. gh-issue: 143387
.. nonce: 9Waopa
.. section: Library

In importlib.metadata, when a distribution file is corrupt and there is no
metadata file, calls to ``Distribution.metadata()`` (including implicit
calls from other properties like ``.name`` and ``.requires``) will now raise
a ``MetadataNotFound`` Exception. This allows callers to distinguish between
missing metadata and a degenerate (empty) metadata. Previously, if the file
was missing, an empty ``PackageMetadata`` would be returned and would be
indistinguishable from the presence of an empty file.

..

.. date: 2026-03-20-14-53-00
.. gh-issue: 146228
.. nonce: OJVEDL
.. section: Library

Cached FastPath objects in importlib.metadata are now cleared on fork,
avoiding broken references to zip files during fork.

..

.. date: 2026-03-20-00-28-00
.. gh-issue: 146171
.. nonce: P5Jk2R7v
.. section: Library

Nested :exc:`AttributeError` suggestions now include property-backed
attributes on nested objects without executing the property getter.

..

.. date: 2026-03-18-23-54-36
.. gh-issue: 145410
.. nonce: NvLWj5
.. section: Library

On Windows, :func:`sysconfig.get_platform` now gets the platform from the
``_sysconfig`` module instead of parsing :data:`sys.version` string. Patch
by Victor Stinner.

..

.. date: 2026-03-18-16-58-17
.. gh-issue: 146091
.. nonce: lBbo1L
.. section: Library

Fix a bug in :func:`termios.tcsetwinsize` where passing a sequence that
raises an exception in ``__getitem__`` would cause a :exc:`SystemError`
instead of propagating the original exception.

..

.. date: 2026-03-17-20-52-24
.. gh-issue: 146083
.. nonce: NxZa_c
.. section: Library

Update bundled `libexpat <https://libexpat.github.io/>`_ to version 2.7.5.

..

.. date: 2026-03-17-20-41-27
.. gh-issue: 146076
.. nonce: yoBNnB
.. section: Library

:mod:`zoneinfo`: fix crashes when deleting ``_weak_cache`` from a
:class:`zoneinfo.ZoneInfo` subclass.

..

.. date: 2026-03-17-19-51-05
.. gh-issue: 123471
.. nonce: oY4UR5
.. section: Library

Make concurrent iteration over :class:`itertools.zip_longest` safe under
free-threading.

..

.. date: 2026-03-17-19-30-45
.. gh-issue: 146075
.. nonce: 85sCSh
.. section: Library

Errors when calling :func:`functools.partial` with a malformed keyword will
no longer crash the interpreter.

..

.. date: 2026-03-17-11-46-20
.. gh-issue: 146054
.. nonce: udYcqn
.. section: Library

Limit the size of :func:`encodings.search_function` cache. Found by OSS Fuzz
in :oss-fuzz:`493449985`.

..

.. date: 2026-03-16-00-00-00
.. gh-issue: 146004
.. nonce: xOptProp
.. section: Library

All :option:`-X` options from the Python command line are now propagated to
child processes spawned by :mod:`multiprocessing`, not just a hard-coded
subset.  This makes the behavior consistent between default "spawn" and
"forkserver" start methods and the old "fork" start method.  The options
that were previously not propagated are: ``context_aware_warnings``,
``cpu_count``, ``disable-remote-debug``, ``int_max_str_digits``,
``lazy_imports``, ``no_debug_ranges``, ``pathconfig_warnings``, ``perf``,
``perf_jit``, ``presite``, ``pycache_prefix``, ``thread_inherit_context``,
and ``warn_default_encoding``.

..

.. date: 2026-03-15-16-38-48
.. gh-issue: 145980
.. nonce: mRze5H
.. section: Library

Added the *alphabet* parameter in :func:`~binascii.b2a_base64`,
:func:`~binascii.a2b_base64`, :func:`~binascii.b2a_base85` and
:func:`~binascii.a2b_base85` and a number of ``*_ALPHABET`` constants in the
:mod:`binascii` module. Removed :func:`!b2a_z85` and :func:`!a2b_z85`.

..

.. date: 2026-03-15-10-17-51
.. gh-issue: 145968
.. nonce: gZexry
.. section: Library

Fix translation in :func:`base64.b64decode` when altchars overlaps with the
standard ones.

..

.. date: 2026-03-15-00-00-00
.. gh-issue: 145966
.. nonce: tCI0uD4I
.. section: Library

Non-:exc:`AttributeError` exceptions raised during dialect attribute lookup
in :mod:`csv` are no longer silently suppressed.

..

.. date: 2026-03-12-21-01-48
.. gh-issue: 145883
.. nonce: lUvXcc
.. section: Library

:mod:`zoneinfo`: Fix heap buffer overflow reads from malformed TZif data.
Found by OSS Fuzz, issues :oss-fuzz:`492245058` and :oss-fuzz:`492230068`.

..

.. date: 2026-03-12-12-17-39
.. gh-issue: 145850
.. nonce: uW3stt
.. section: Library

Changed some implementation details in :class:`struct.Struct`: calling it
with non-ASCII string format will now raise a :exc:`ValueError` instead of
:exc:`UnicodeEncodeError`, calling it with non-ASCII bytes format will now
raise a :exc:`ValueError` instead of :exc:`struct.error`, getting the
:attr:`!format` attribute of uninitialized object will now raise an
:exc:`AttributeError` instead of :exc:`RuntimeError`.

..

.. date: 2026-03-11-10-25-32
.. gh-issue: 123720
.. nonce: TauFRx
.. section: Library

asyncio: Fix :func:`asyncio.Server.serve_forever` shutdown regression. Since
3.12, cancelling ``serve_forever()`` could hang waiting for a handler
blocked on a read from a client that never closed (effectively requiring two
interrupts to stop); the shutdown sequence now ensures client streams are
closed so ``serve_forever()`` exits promptly and handlers observe EOF.

..

.. date: 2026-03-10-19-50-59
.. gh-issue: 138122
.. nonce: CsoBEo
.. section: Library

The ``profiling.sampling`` module now supports differential flamegraph
visualization via ``--diff-flamegraph`` to compare two profiling runs.
Functions are colored red (regressions), blue (improvements), gray
(neutral), or purple (new). Elided stacks show code paths that disappeared
between runs.

..

.. date: 2026-03-10-14-57-15
.. gh-issue: 145754
.. nonce: YBL5Ko
.. section: Library

Request signature during mock autospec with ``FORWARDREF`` annotation
format. This prevents runtime errors when an annotation uses a name that is
not defined at runtime.

..

.. date: 2026-03-10-14-13-12
.. gh-issue: 145750
.. nonce: iQsTeX
.. section: Library

Avoid undefined behaviour from signed integer overflow when parsing format
strings in the :mod:`struct` module. Found by OSS Fuzz in
:oss-fuzz:`488466741`.

..

.. date: 2026-03-10-01-54-34
.. gh-issue: 145719
.. nonce: okJRoK
.. section: Library

Add ``application/efi`` MIME type to :mod:`mimetypes`.

..

.. date: 2026-03-10-01-48-12
.. gh-issue: 145717
.. nonce: dPc0Rt
.. section: Library

Add a few Microsoft-specific MIME types.

..

.. date: 2026-03-09-19-59-05
.. gh-issue: 145703
.. nonce: 4EEP7J
.. section: Library

:mod:`asyncio`: Make sure that :meth:`loop.call_at <asyncio.loop.call_at>`
and :meth:`loop.call_later <asyncio.loop.call_later>` trigger scheduled
events on time when the clock resolution becomes too small.

..

.. date: 2026-03-09-18-33-16
.. gh-issue: 145697
.. nonce: d6hFmm
.. section: Library

Add ``application/sql`` and ``application/vnd.sqlite3`` into ``mimetypes``.

..

.. date: 2026-03-09-00-00-00
.. gh-issue: 145492
.. nonce: 457Afc
.. section: Library

Fix infinite recursion in :class:`collections.defaultdict` ``__repr__`` when
a ``defaultdict`` contains itself. Based on analysis by KowalskiThomas in
:gh:`145492`.

..

.. date: 2026-03-08-00-00-00
.. gh-issue: 145650
.. nonce: LgRepr
.. section: Library

Add :meth:`~object.__repr__` support to :class:`logging.Formatter` and
:class:`logging.Filter`, showing the format string and filter name
respectively.

..

.. date: 2026-03-07-14-34-39
.. gh-issue: 145587
.. nonce: flFQ5-
.. section: Library

Resolved a performance regression in ``multiprocessing.connection.wait`` on
Windows that caused infinite busy loops when called with no objects. The
function now properly yields control to the OS to conserve CPU resources.
Patch By Shrey Naithani

..

.. date: 2026-03-07-02-44-52
.. gh-issue: 145616
.. nonce: x8Mf23
.. section: Library

Detect Android sysconfig ABI correctly on 32-bit ARM Android on 64-bit ARM
kernel

..

.. date: 2026-03-05-14-13-10
.. gh-issue: 145546
.. nonce: 3tnlxx
.. section: Library

Fix ``unittest.util.sorted_list_difference()`` to deduplicate remaining
elements when one input list is exhausted before the other.

..

.. date: 2026-03-03-23-21-40
.. gh-issue: 145446
.. nonce: 0c-TJX
.. section: Library

Now :mod:`functools` is safer in free-threaded build when using keywords in
:func:`functools.partial`

..

.. date: 2026-02-26-20-13-16
.. gh-issue: 145264
.. nonce: 4pggX_
.. section: Library

Base64 decoder (see :func:`binascii.a2b_base64`, :func:`base64.b64decode`,
etc) no longer ignores excess data after the first padded quad in non-strict
(default) mode.  Instead, in conformance with :rfc:`4648`, section 3.3, it
now ignores the pad character, "=", if it is present before the end of the
encoded data.

..

.. date: 2026-02-23-21-28-12
.. gh-issue: 145035
.. nonce: J5UjS6
.. section: Library

Allows omitting the internal library ``_pyrepl`` with limited loss of
functionality. This allows complete removal of the modern REPL, which is an
unsupported configuration, but still desirable for some distributions.

..

.. date: 2026-02-19-16-34-18
.. gh-issue: 144270
.. nonce: wJRtSr
.. section: Library

Made the *tag* parameter of :class:`xml.etree.ElementTree.Element` and the
*parent* and *tag* parameters of :func:`xml.etree.ElementTree.SubElement`
positional-only, matching the behavior of the C accelerator.

..

.. date: 2026-02-19-12-00-00
.. gh-issue: 144984
.. nonce: b93995c982
.. section: Library

Fix crash in :meth:`xml.parsers.expat.xmlparser.ExternalEntityParserCreate`
when an allocation fails. The error paths could dereference NULL
``handlers`` and double-decrement the parent parser's reference count.

..

.. date: 2026-02-18-21-45-00
.. gh-issue: 144975
.. nonce: Ab3XyZ
.. section: Library

:meth:`wave.Wave_write.setframerate` now validates the frame rate after
rounding to an integer, preventing values like ``0.5`` from being accepted
and causing confusing errors later. Patch by Michiel Beijen.

..

.. date: 2026-02-17-03-43-07
.. gh-issue: 140715
.. nonce: twmcM_
.. section: Library

Add ``%n`` and ``%t`` support to :meth:`~datetime.datetime.strptime`.

..

.. date: 2026-02-11-21-01-30
.. gh-issue: 144259
.. nonce: OAhOR8
.. section: Library

Fix inconsistent display of long multiline pasted content in the REPL.

..

.. date: 2026-02-08-22-04-06
.. gh-issue: 140814
.. nonce: frzSpn
.. section: Library

:func:`multiprocessing.freeze_support` no longer sets the default start
method as a side effect, which previously caused a subsequent
:func:`multiprocessing.set_start_method` call to raise :exc:`RuntimeError`.

..

.. date: 2026-02-04-20-30-59
.. gh-issue: 123471
.. nonce: 1dnPvs
.. section: Library

Make concurrent iteration over :class:`itertools.accumulate` safe under
free-threading.

..

.. date: 2026-01-10-16-23-21
.. gh-issue: 143715
.. nonce: HZrfSA
.. section: Library

Calling the ``Struct.__new__()`` without required argument now is
deprecated. Calling :meth:`~object.__init__` method on initialized
:class:`~struct.Struct` objects is deprecated.

..

.. date: 2025-12-18-00-00-00
.. gh-issue: 142763
.. nonce: AJpZPVG5
.. section: Library

Fix a race condition between :class:`zoneinfo.ZoneInfo` creation and
:func:`zoneinfo.ZoneInfo.clear_cache` that could raise :exc:`KeyError`.

..

.. date: 2025-11-18-06-35-53
.. gh-issue: 141707
.. nonce: DBmQIy
.. section: Library

Don't change :class:`tarfile.TarInfo` type from ``AREGTYPE`` to ``DIRTYPE``
when parsing GNU long name or link headers.

..

.. date: 2025-11-15-23-14-30
.. gh-issue: 138577
.. nonce: KbShrt
.. section: Library

:func:`getpass.getpass` with non-empty ``echo_char`` now handles keyboard
shortcuts including Ctrl+A/E (cursor movement), Ctrl+K/U (kill line), Ctrl+W
(erase word), and Ctrl+V (literal next) by reading the terminal's control
character settings and processing them appropriately in non-canonical mode.
Patch by Sanyam Khurana.

..

.. date: 2025-10-13-16-43-36
.. gh-issue: 140049
.. nonce: VvmAzN
.. section: Library

:func:`traceback.format_exception_only` now colorizes exception notes.

..

.. date: 2025-10-11-11-50-59
.. gh-issue: 139933
.. nonce: 05MHlx
.. section: Library

Improve :exc:`AttributeError` suggestions for classes with a custom
:meth:`~object.__dir__` method returning a list of unsortable values. Patch
by Bénédikt Tran.

..

.. date: 2025-10-05-15-38-02
.. gh-issue: 139633
.. nonce: l3P839
.. section: Library

The :mod:`netrc` security check is now run once per parse rather than once
per entry.

..

.. date: 2025-09-19-13-54-54
.. gh-issue: 130472
.. nonce: LODfdk
.. section: Library

Add fancycompleter and enable it by default when using pyrepl. This gives
colored tab completion.

..

.. date: 2025-02-07-00-48-07
.. gh-issue: 112632
.. nonce: 95MM0C
.. section: Library

Add an *expand* keyword argument for :func:`pprint.pprint`,
:func:`pprint.pformat`, :func:`pprint.pp` by passing on all *kwargs* and
:class:`pprint.PrettyPrinter`. Contributed by Stefan Todoran and Semyon
Moroz.

..

.. date: 2024-09-25-12-47-50
.. gh-issue: 66419
.. nonce: DVSukU
.. section: Library

Optional argument with :ref:`nargs` equals to ``argparse.REMAINDER`` now
consumes all remaining arguments including ``'--'``.

..

.. date: 2023-03-10-13-10-06
.. gh-issue: 60729
.. nonce: KCCHTe
.. section: Library

Add support for floating point audio wave files in :mod:`wave`.

..

.. bpo: 36461
.. date: 2019-04-25-21-11-37
.. nonce: TO5YyP
.. section: Library

Make the target time of :meth:`timeit.Timer.autorange` configurable and add
``--target-time`` option to the command-line interface of :mod:`timeit`.

..

.. date: 2026-03-25-00-00-00
.. gh-issue: 126676
.. nonce: 052336
.. section: Documentation

Expand :mod:`argparse` documentation for ``type=bool`` with a demonstration
of the surprising behavior and pointers to common alternatives.

..

.. date: 2026-03-09-00-00-00
.. gh-issue: 145649
.. nonce: 8BcbAB
.. section: Documentation

Fix text wrapping and formatting of ``-X`` option descriptions in the
:manpage:`python(1)` man page by using proper roff markup.

..

.. date: 2026-04-03-21-37-18
.. gh-issue: 144418
.. nonce: PusC0S
.. section: Tests

The Android testbed's emulator RAM has been increased from 2 GB to 4 GB.

..

.. date: 2026-03-24-00-15-58
.. gh-issue: 146202
.. nonce: LgH6Bj
.. section: Tests

Fix a race condition in regrtest: make sure that the temporary directory is
created in the worker process. Previously, temp_cwd() could fail on Windows
if the "build" directory was not created.  Patch by Victor Stinner.

..

.. date: 2026-03-28-02-48-51
.. gh-issue: 146541
.. nonce: k-zlM6
.. section: Build

The Android testbed can now be built for 32-bit ARM and x86 targets.

..

.. date: 2026-03-27-06-55-10
.. gh-issue: 146498
.. nonce: uOiCab
.. section: Build

The iOS XCframework build script now ensures libpython isn't included in
installed app content, and is more robust in identifying standard library
binary content that requires processing.

..

.. date: 2026-03-26-14-35-29
.. gh-issue: 146450
.. nonce: 9Kmp5Q
.. section: Build

The Android build script was modified to improve parity with other platform
build scripts.

..

.. date: 2026-03-26-12-48-42
.. gh-issue: 146446
.. nonce: 0GyMu4
.. section: Build

The clean target for the Apple/iOS XCframework build script is now more
selective when targeting a single architecture.

..

.. date: 2026-03-26-12-27-42
.. gh-issue: 146444
.. nonce: JKJuEa
.. section: Build

The Apple/iOS build script has been moved to the Platforms directory.

..

.. date: 2026-03-23-20-06-35
.. gh-issue: 146210
.. nonce: C01Rmq
.. section: Build

Fix building the jit stencils on Windows when the interpreter is built with
a different clang version. Patch by Chris Eibl.

..

.. date: 2026-03-12-12-30-24
.. gh-issue: 145844
.. nonce: VOPeCU
.. section: Build

Update to WASI SDK 32.

..

.. date: 2026-03-11-11-58-42
.. gh-issue: 145801
.. nonce: iCXa3v
.. section: Build

When Python build is optimized with GCC using PGO, use
``-fprofile-update=atomic`` option to use atomic operations when updating
profile information. This option reduces the risk of gcov Data Files (.gcda)
corruption which can cause random GCC crashes. Patch by Victor Stinner.

..

.. date: 2026-03-10-16-58-55
.. gh-issue: 138850
.. nonce: CkqTw6
.. section: Build

Add :option:`--disable-epoll` to ``configure``

..

.. date: 2026-03-08-06-18-26
.. gh-issue: 145633
.. nonce: Ogu-RF
.. section: Build

Remove support for ancient ARM platforms (ARMv4L and ARMv5L OABI boards),
using mixed-endian representation for doubles.  Patch by Sergey B Kirpichev.

..

.. date: 2026-01-08-22-27-07
.. gh-issue: 85277
.. nonce: TotySi
.. section: Build

Fix building without ``stropts.h`` or empty ``stropts.h``

..

.. date: 2025-10-19-23-44-46
.. gh-issue: 140131
.. nonce: AABF2k
.. section: Windows

Fix REPL cursor position on Windows when module completion suggestion line
hits console width.

..

.. date: 2025-10-17-01-07-03
.. gh-issue: 137586
.. nonce: kVzxvp
.. section: macOS

Invoke :program:`osascript` with absolute path in :mod:`webbrowser` and
:mod:`!turtledemo`.

..

.. date: 2026-03-22-00-00-00
.. gh-issue: 135953
.. nonce: IptOwg
.. section: Tools/Demos

Properly identify the main thread in the Gecko profiler collector by using a
status flag from the interpreter state instead of relying on
:func:`threading.main_thread` in the collector process.

..

.. date: 2026-03-15-20-59-29
.. gh-issue: 145976
.. nonce: rEdUI-
.. section: Tools/Demos

Remove :file:`Misc/indent.pro`, a configuration file for GNU
:manpage:`indent(1)`.

..

.. date: 2026-03-15-11-32-35
.. gh-issue: 145976
.. nonce: mqhzmB
.. section: Tools/Demos

Remove :file:`Misc/vgrindefs` and :file:`Misc/Porting`.

..

.. date: 2026-03-31-13-33-41
.. gh-issue: 146636
.. nonce: 5do3wt
.. section: C API

The :c:data:`Py_mod_abi` slot is now mandatory for modules created from a
slots array (using :c:func:`PyModule_FromSlotsAndSpec` or the
:c:func:`PyModExport_* <PyModExport_modulename>` export hook).

..

.. date: 2026-03-19-16-50-27
.. gh-issue: 146175
.. nonce: pISQGX
.. section: C API

The following macros are :term:`soft deprecated`: :c:macro:`Py_ALIGNED`,
:c:macro:`PY_FORMAT_SIZE_T`, :c:macro:`Py_LL`, :c:macro:`Py_ULL`,
:c:macro:`PY_LONG_LONG`, :c:macro:`PY_LLONG_MIN`, :c:macro:`PY_LLONG_MAX`,
:c:macro:`PY_ULLONG_MAX`, :c:macro:`PY_INT32_T`, :c:macro:`PY_UINT32_T`,
:c:macro:`PY_INT64_T`, :c:macro:`PY_UINT64_T`, :c:macro:`PY_SIZE_MAX`,
:c:macro:`Py_UNICODE_SIZE`, :c:macro:`Py_VA_COPY`.

The macro :c:macro:`Py_UNICODE_WIDE`, which was scheduled for removal, is
:term:`soft deprecated` instead.

..

.. date: 2026-03-18-23-44-29
.. gh-issue: 146143
.. nonce: pwIrJq
.. section: C API

:c:func:`PyUnicodeWriter_WriteUCS4` now accepts a pointer to a constant
buffer of ``Py_UCS4``.

..

.. date: 2026-03-18-20-18-59
.. gh-issue: 146056
.. nonce: nnZIgp
.. section: C API

:c:func:`PyUnicodeWriter_WriteRepr` now supports ``NULL`` argument.

..

.. date: 2026-02-19-18-39-11
.. gh-issue: 145010
.. nonce: mKzjci
.. section: C API

Use GCC dialect alternatives for inline assembly in ``object.h`` so that the
Python headers compile correctly with ``-masm=intel``.