Inherited, overridden attribute type reverted to the top parent class type

The issue type is probably quite bad, but example should quickly clear things up:

class A:
    attr = None


class B(A):
    attr: str  # type: ignore


class C1(B):
    attr = "test"


class C2(B):
    pass


class D(C2):
    attr = "test"

mypy test.py outputs:

test.py:18: error: Incompatible types in assignment (expression has type "str", base class "A" defined the type as "None")

where line 18 is the last line of above example

As to why I do attr: str # type: ignore - in a nutshell, in my case A class comes from external source and they botched type hints there so I try to fix them in B. Not sure if it should have worked for C1, but if it did I see it breaking in D as a bug due mypy not being consistent, but then again maybe there is a good reason for it?.

Tested with mypy 0.720

Commencez par exécuter l’exemple d’héritage fourni avec mypy 0.720 et comparez les diagnostics pour C1 et D. Suivez la résolution des types pour les attributs hérités et redéfinis, puis confirmez que le comportement obtenu est cohérent avec la sémantique prévue décrite dans l’issue.