The following code causes an assertion failure:
import os
os.__name__ = None
os.does_not_exist

this is because module_getattro() (in Objects/moduleobject.c) assumes that
__name__ is a string, and passes it to PyErr_Format(), which asserts it is a
string.


if we fixed that one (so that the code above would raise an AttributeError),
the following code would still cause an assertion failure:

import os
os.__name__ = None
from os import does_not_exist


this is because import_from() (in Python/ceval.c) also assumes that __name__
is a string, and passes it to PyUnicode_FromFormat(), which asserts it is a
string.


BTW, while we are in module_getattro(): isn't the second call to PyErr_Clear()
redundant? (Ethan, IIUC, you worked on this as part of #8297 some years ago..)

New changeset 6db7033192cd537ca987a65971acb01206c3ba82 by Serhiy Storchaka (Oren Milman) in branch 'master':
bpo-31492: Fix assertion failures in case of a module with a bad __name__ attribute. (#3620)
https://github.com/python/cpython/commit/6db7033192cd537ca987a65971acb01206c3ba82

New changeset f0db2dfda777ad3380e7816cabe4c4240f31687f by Serhiy Storchaka in branch '3.6':
[3.6] bpo-31492: Fix assertion failures in case of a module with a bad __name__ attribute. (GH-3620). (#3773)
https://github.com/python/cpython/commit/f0db2dfda777ad3380e7816cabe4c4240f31687f