gh-145119: Allow frozendict to be assigned to instance __dict__ by mohsinm-dev · Pull Request #145123 · python/cpython

Avoid frozendict dict on objects mutating their own dict

Allowing _PyObject_SetDict() to accept PyAnyDict_Check here makes frozendict assignable to every PyObject_GenericSetDict user, but some of those types still perform internal writes with PyDict_SetItem/PyDict_DelItem (for example descriptor_get_wrapped_attribute and descriptor_set_wrapped_attribute in Objects/funcobject.c for classmethod/staticmethod annotation caching). PyDict_SetItem still rejects frozendict with PyErr_BadInternalCall, so after obj.__dict__ = frozendict(...), operations like reading or updating __annotations__ can now raise SystemError instead of behaving normally or reporting an intentional immutability error.

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