3.15.0a4

.. 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.

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.. 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.

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.. 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.

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.. 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

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.. 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.

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.. 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.

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.. 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.

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.. 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.

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.. 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.

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.. 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.

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.. 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.

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.. 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.

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.. 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

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.. 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.

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.. 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.

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.. 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.

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.. 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.

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.. 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.

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.. 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.

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.. 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

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.. 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.

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.. 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.

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.. 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).

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

Fix a file descriptor leak in import.c

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

Fix building JIT stencils on free-threaded builds.

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.. 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.

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.. 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.

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.. 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.

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.. 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.

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

Eliminate redundant refcounting from _LOAD_ATTR_INSTANCE_VALUE.

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

Eliminate redundant refcounting from _STORE_ATTR_WITH_HINT.

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.. 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.

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.. 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.

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.. 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.