Incompatible types in assignment with User subclass

[zacchiro]

Heya, I've this class deriving from the (concrete) User class:

from django.contrib.auth.models import User, UserManager

class DepositClient(User):
    objects = UserManager()

mypy with django-stubs 1.1.0 is complaining on the objects line that:

error: Incompatible types in assignment
(expression has type "UserManager[DepositClient]",
base class "User" defined the type as "UserManager[User]")

even if DepositClient is a subclass of User and the type variable in Manager is declared as covariant by django-stubs.

This should work out-of-the-box with django-stubs, right?
Or am I missing something here?

[mkurnikov]

This is a case specified in the https://github.com/typeddjango/django-stubs/blob/master/test-data/typecheck/managers/test_managers.yml#L281
It's a mypy limitation, smth around Liskov incompatibility.

[zacchiro]

On Mon, Sep 23, 2019 at 09:37:11AM -0700, Maxim Kurnikov wrote: This is a case specified in the https://github.com/typeddjango/django-stubs/blob/master/test-data/typecheck/managers/test_managers.yml#L281 It's a mypy limitation, smth around Liskov incompatibility.

So what is the recommended way to go about these? # type: ignore ?

[mkurnikov]

Yes, # type: ignore + manual annotation I believe would work (can't test right now).
Until python/mypy#7468 is fixed.