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Add whatsnew text for warnings module changes. (gh-135869)

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Neil Schemenauer 2025-06-25 20:03:24 -07:00 • committed by GitHub
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Doc/whatsnew/3.14.rst
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@ -978,6 +978,23 @@ be specified by the build backend, as it will no longer be determined
automatically by the C compiler. For a running interpreter, the setting that
was used at compile time can be found using :func:`sysconfig.get_config_var`.
A new flag has been added, :data:`~sys.flags.context_aware_warnings`. This
flag defaults to true for the free-threaded build and false for the GIL-enabled
build. If the flag is true then the :class:`warnings.catch_warnings` context
manager uses a context variable for warning filters. This makes the context
manager behave predicably when used with multiple threads or asynchronous
tasks.
A new flag has been added, :data:`~sys.flags.thread_inherit_context`. This flag
defaults to true for the free-threaded build and false for the GIL-enabled
build. If the flag is true then threads created with :class:`threading.Thread`
start with a copy of the :class:`~contextvars.Context()` of the caller of
:meth:`~threading.Thread.start`. Most significantly, this makes the warning
filtering context established by :class:`~warnings.catch_warnings` be
"inherited" by threads (or asyncio tasks) started within that context. It also
affects other modules that use context variables, such as the :mod:`decimal`
context manager.
.. _whatsnew314-pyrepl-highlighting:
@ -1028,6 +1045,18 @@ Please report any bugs or major performance regressions that you encounter!
.. seealso:: :pep:`744`
Concurrent safe warnings control
--------------------------------
The :class:`warnings.catch_warnings` context manager will now optionally
use a context variable for warning filters. This is enabled by setting
the :data:`~sys.flags.context_aware_warnings` flag, either with the ``-X``
command-line option or an environment variable. This gives predicable
warnings control when using :class:`~warnings.catch_warnings` combined with
multiple threads or asynchronous tasks. The flag defaults to true for the
free-threaded build and false for the GIL-enabled build.
(Contributed by Neil Schemenauer and Kumar Aditya in :gh:`130010`.)
Other language changes
======================