bpo-42406: Fix whichmodule() with multiprocessing

[renatolfc]

This fixes the behavior of the pickle.whichmodule() function when multiprocessing is imported before the pickle module.

Prior to this patch, the following incorrect output would be found when trying to determine the module of the (for example) gdtrix function:

>>> import multiprocessing
>>> import pickle
>>> from scipy.special import gdtrix
>>> pickle.whichmodule(gdtrix, gdtrix.__name__)
'__mp_main__'

With the patch, now we get correct behavior:

>>> import multiprocessing
>>> import pickle
>>> from scipy.special import gdtrix
>>> pickle.whichmodule(gdtrix, gdtrix.__name__)
'scipy.special._ufuncs'

This also fixes uqfoundation/dill#392.

Signed-off-by: Renato L. de F. Cunha renatoc@br.ibm.com

https://bugs.python.org/issue42406

Automerge-Triggered-By: GH:gpshead

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[gpshead]

i made one minor edit to mention bpo-42406 in a comment and prefer () over .

[miss-islington]

@renatolfc: Status check is done, and it's a success ❌ .

[miss-islington]

@renatolfc: Status check is done, and it's a success ❌ .

[miss-islington]

@renatolfc: Status check is done, and it's a success ❌ .

[miss-islington]

@renatolfc: Status check is done, and it's a success ❌ .

[miss-islington]

Thanks @renatolfc for the PR, and @gpshead for merging it 🌮🎉.. I'm working now to backport this PR to: 3.8, 3.9.
🐍🍒⛏🤖

[bedevere-bot]

GH-23560 is a backport of this pull request to the 3.9 branch.

[bedevere-bot]

GH-23561 is a backport of this pull request to the 3.8 branch.