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nascheme merged 2 commits into from
Jun 26, 2025
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Add whatsnew text for warnings module changes. #135869

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Add whatsnew text for warnings module changes.
nascheme Jun 23, 2025
c9e788c
Move notes about new sys flags into FT section.
nascheme Jun 24, 2025
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24 changes: 24 additions & 0 deletions Doc/whatsnew/3.14.rst
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Expand Up @@ -122,6 +122,18 @@ it's safe to do so. This can lead to different values returned from
:func:`sys.getrefcount` and :c:func:`Py_REFCNT` compared to previous versions
of Python. See :ref:`below <whatsnew314-refcount>` for details.

A new flag has been added, :data:`~sys.flags.context_aware_warnings`. This
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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.

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`.


New features
============

Expand Down Expand Up @@ -1028,6 +1040,18 @@ 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
======================
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