New submission from Renato Cunha <ren...@renatocunha.com>:
Importing multiprocessing prior to other modules that define `ufunc`s breaks
pickle.whichmodule for those functions.
Example:
Python 3.8.6 (default, Sep 30 2020, 04:00:38)
[GCC 10.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import multiprocessing
>>> from scipy.special import gdtrix
>>> from pickle import whichmodule
>>> whichmodule(gdtrix, gdtrix.__name__)
'__mp_main__'
Now, if we change the order of imports, whichmodule works fine:
Python 3.8.6 (default, Sep 30 2020, 04:00:38)
[GCC 10.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from scipy.special import gdtrix
>>> from pickle import whichmodule
>>> import multiprocessing
>>> whichmodule(gdtrix, gdtrix.__name__)
'scipy.special._ufuncs'
This happens because multiprocessing creates an alias to `__main__` when
imported:
Lib/multiprocessing/__init__.py
37: sys.modules['__mp_main__'] = sys.modules['__main__']
But doing so changes the ordering of `sys.modules`, and `whichmodule` returns
`__mp_main__` instead of the correct `scipy.special._ufuncs`.
This bug has arisen in the context of using `dill` (which imports
multiprocessing) for serialization and is further documented at
https://github.com/uqfoundation/dill/issues/392.
I intend to submit a patch/PR with a fix soon.
----------
components: Interpreter Core
messages: 381410
nosy: renatolfc
priority: normal
severity: normal
status: open
title: Importing multiprocessing breaks pickle.whichmodule
type: behavior
versions: Python 3.10, Python 3.6, Python 3.7, Python 3.8, Python 3.9
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue42406>
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