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gh-135583: Document mock.patch with multiprocessing start methods #152881

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Document mock.patch with multiprocessing start methods
hrimov Jul 2, 2026
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Merge branch 'main' into document-patch-with-multiprocessing
hrimov Jul 2, 2026
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16 changes: 16 additions & 0 deletions Doc/library/unittest.mock.rst
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Expand Up @@ -2036,6 +2036,22 @@ that proxy attribute access, like the `django settings object
<https://web.archive.org/web/20200603181648/http://www.voidspace.org.uk/python/weblog/arch_d7_2010_12_04.shtml#e1198>`_.


Patching with multiprocessing
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

:func:`patch` modifies objects in the current process's memory. Patches are
not inherited by child processes created with the ``"forkserver"`` or
``"spawn"`` :mod:`multiprocessing` start methods.

To apply patches in child processes, use a pool initializer::

def init_worker():
mock.patch.object(MyClass, "method", return_value=42).start()

with multiprocessing.Pool(initializer=init_worker) as pool:
pool.map(my_func, range(5))


MagicMock and magic method support
----------------------------------

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