dataclasses: implicitly defined __dict__ and __weakref__ slots of inherited classes are ignored.

Bug report

The weakref slot is redefined when inherited from a class which didn't specify slots at all (and thus has a dict and weakref slots).

from dataclasses import dataclass class A: pass @dataclass(slots=True, weakref_slot=True) class B(A): pass

gives the following error:

TypeError: __weakref__ slot disallowed: either we already got one, or __itemsize__ != 0