diff --git a/Lib/pickle.py b/Lib/pickle.py index af50a9b0c06bb0..05f30b6b168b5c 100644 --- a/Lib/pickle.py +++ b/Lib/pickle.py @@ -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: diff --git a/Misc/NEWS.d/next/Library/2020-11-19-10-44-41.bpo-42406.r9rNCj.rst b/Misc/NEWS.d/next/Library/2020-11-19-10-44-41.bpo-42406.r9rNCj.rst new file mode 100644 index 00000000000000..c157df138a5ea0 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2020-11-19-10-44-41.bpo-42406.r9rNCj.rst @@ -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.