[Python-Dev] PEP 489: module m_traverse called with NULL module state

Antoine Pitrou solipsis at pitrou.net
Wed Dec 13 15:15:40 EST 2017


After debugging a crash on AppVeyor for a submitter's PR
(see https://github.com/python/cpython/pull/4611 ), I came to the
following diagnosis: converting the "atexit" module (which is a
built-in C extension) to PEP 489 multiphase initialization can lead to
its m_traverse function (and presumably also m_clear and m_free) to be
called while not module state is yet registered: that is,
`PyModule_GetState(self)` when called from m_traverse returns NULL!

Is that an expected or known subtlety?



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