Type cache can expose previous values during finalization of an object

Bug report

Bug description:

This should always print True, that is an attribute accessed from a class should match the value that's in the type's mappingproxy:

class X:
    def __del__(inner_self):
        v = C.a
        print(v == C.__dict__['a'])

class C:
    a = X()

# prime the cache
C.a
C.a

# destructor shouldn't be able to see inconsisent state
C.a = X()
C.a = X()

But this prints False because the destructor can be run when the assignment into the type dict occurs, but before the type version is invalidated.

CPython versions tested on:

3.8, CPython main branch

Operating systems tested on:

Linux

Commencez par exécuter le reproducer sur CPython main et comparez la recherche d’attributs avec le mappage des types pendant le destructeur déclenché par l’affectation. Suivez l’invalidation du cache des types et la séquence de finalisation ; le travail est terminé lorsque l’exemple affiche systématiquement True sans exposer l’état incohérent.