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[3.8] bpo-42406: Fix whichmodule() with multiprocessing (GH-23403) #23561

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Merged
merged 1 commit into from
Nov 29, 2020
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[3.8] bpo-42406: Fix whichmodule() with multiprocessing (GH-23403) #23561

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4 changes: 3 additions & 1 deletion Lib/pickle.py
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Original file line number Diff line number Diff line change
Expand Up @@ -340,7 +340,9 @@ def whichmodule(obj, name):
# Protect the iteration by using a list copy of sys.modules against dynamic
# modules that trigger imports of other modules upon calls to getattr.
for module_name, module in sys.modules.copy().items():
if module_name == '__main__' or module is None:
if (module_name == '__main__'
or module_name == '__mp_main__' # bpo-42406
or module is None):
continue
try:
if _getattribute(module, name)[0] is obj:
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2020-11-19-10-44-41.bpo-42406.r9rNCj.rst
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@@ -0,0 +1,3 @@
We fixed an issue in `pickle.whichmodule` in which importing
`multiprocessing` could change the how pickle identifies which module an
object belongs to, potentially breaking the unpickling of those objects.