Python 3.9: all versions and old releases

Core and Builtins
- gh-92311: Fixed a bug where setting frame.f_lineno to jump over a list comprehension could misbehave or crash.
- gh-92112: Fix crash triggered by an evil custom mro() on a metaclass.
- gh-92036: Fix a crash in subinterpreters related to the garbage collector. When a subinterpreter is deleted, untrack all objects tracked by its GC. To prevent a crash in deallocator functions expecting objects to be tracked by the GC, leak a strong reference to these objects on purpose, so they are never deleted and their deallocator functions are not called. Patch by Victor Stinner.
- gh-91421: Fix a potential integer overflow in _Py_DecodeUTF8Ex.
- bpo-46775: Some Windows system error codes(>= 10000) are now mapped into the correct errno and may now raise a subclass of OSError. Patch by Dong-hee Na.
- bpo-46962: Classes and functions that unconditionally declared their docstrings ignoring the --without-doc-strings compilation flag no longer do so.
The classes affected are pickle.PickleBuffer, testcapi.RecursingInfinitelyError, and types.GenericAlias.
The functions affected are 24 methods in ctypes.
Patch by Oleg Iarygin.
- bpo-36819: Fix crashes in built-in encoders with error handlers that return position less or equal than the starting position of non-encodable characters.
Library
- gh-91581: utcfromtimestamp() no longer attempts to resolve fold in the pure Python implementation, since the fold is never 1 in UTC. In addition to being slightly faster in the common case, this also prevents some errors when the timestamp is close to datetime.min. Patch by Paul Ganssle.
- gh-92530: Fix an issue that occurred after interrupting threading.Condition.notify().
- gh-92049: Forbid pickling constants re._constants.SUCCESS etc. Previously, pickling did not fail, but the result could not be unpickled.
- bpo-47029: Always close the read end of the pipe used by multiprocessing.Queue after the last write of buffered data to the write end of the pipe to avoid BrokenPipeError at garbage collection and at multiprocessing.Queue.close() calls. Patch by Géry Ogam.
- gh-91910: Add missing f prefix to f-strings in error messages from the multiprocessing and asyncio modules.
- gh-91810: ElementTree method write() and function tostring() now use the text file’s encoding (“UTF-8” if not available) instead of locale encoding in XML declaration when encoding="unicode" is specified.
- gh-91832: Add required attribute to argparse.Action repr output.
- gh-91734: Fix OSS audio support on Solaris.
- gh-91700: Compilation of regular expression containing a conditional expression (?(group)...) now raises an appropriate re.error if the group number refers to not defined group. Previously an internal RuntimeError was raised.
- gh-91676: Fix unittest.IsolatedAsyncioTestCase to shutdown the per test event loop executor before returning from its run method so that a not yet stopped or garbage collected executor state does not persist beyond the test.
- gh-90568: Parsing \N escapes of Unicode Named Character Sequences in a regular expression raises now re.error instead of TypeError.
- gh-91595: Fix the comparison of character and integer inside Tools.gdb.libpython.write_repr(). Patch by Yu Liu.
- gh-90622: Worker processes for concurrent.futures.ProcessPoolExecutor are no longer spawned on demand (a feature added in 3.9) when the multiprocessing context start method is "fork" as that can lead to deadlocks in the child processes due to a fork happening while threads are running.
- gh-91575: Update case-insensitive matching in the re module to the latest Unicode version.
- gh-91581: Remove an unhandled error case in the C implementation of calls to datetime.fromtimestamp with no time zone (i.e. getting a local time from an epoch timestamp). This should have no user-facing effect other than giving a possibly more accurate error message when called with timestamps that fall on 10000-01-01 in the local time. Patch by Paul Ganssle.
- bpo-34480: Fix a bug where _markupb