3.15.0a3 - Cpython — ContextQMD

.. 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: 2025-09-09-13-00-42 .. 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.