Annotating GenericAPIView.filter_queryset fails since v3.16.9

[pai-martinreidemeister]

Bug report

What's wrong

I don't know how to annotate rest_framework.generics.GenericAPIView.filter_queryset. Before 3.16.9 we did this:

from typing import override
from django.db.models import QuerySet
from rest_framework import viewsets
from foo.models import MyModel

class MyModelViewSet(viewsets.ModelViewSet[MyModel]):
    queryset = MyModel.objects.all()
    filterset_fields = ('name',)

    @override
    def filter_queryset(self, queryset: QuerySet[MyModel]) -> QuerySet[MyModel]:
        qs = super().filter_queryset(queryset)
        return qs

But since 3.16.9 we get this error:

$ mypy .
/path/to/foo/views_rest.py:12: error: Return type "QuerySet[MyModel, MyModel]" of "filter_queryset" incompatible with return type "QuerySet[MyModel, _Row]" in supertype
"rest_framework.generics.GenericAPIView"  [override]
        def filter_queryset(self, queryset: QuerySet[MyModel]) -> QuerySet[MyModel]:
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/path/to/foo/views_rest.py:12: error: Argument 1 of "filter_queryset" is incompatible with supertype "rest_framework.generics.GenericAPIView"; supertype defines the argument type as
"QuerySet[MyModel, _Row]"  [override]
        def filter_queryset(self, queryset: QuerySet[MyModel]) -> QuerySet[MyModel]:
                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~
/path/to/foo/views_rest.py:12: note: This violates the Liskov substitution principle
/path/to/foo/views_rest.py:12: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#incompatible-overrides
Found 2 errors in 1 file (checked 13 source files)

I assume that #916 is the cause.

How is that should be

There should be no error.

System information

• OS:
• python version: 3.13.12
• django version: 6.0.3
• mypy version: 1.20.1
• django-stubs version: 6.0.2

[intgr]

@brianhelba any ideas?

[brianhelba]

Yes, I agree this was caused by #916.

I think that to be strictly correct, the downstream code should change to the two-argument generic syntax. However, requiring everyone to explicitly annotate all QuerySet using a two-argument form is a bad user experience. Python type annotations have a bad reputation even when they're simple and intuitive, and the two-argument syntax is not obvious at first (to be fair, the syntax is ultimately dictated by Django's behavior and the model created by django-stubs, which we can't control).

So, I'm open to reverting some or all of #916, but let me see if there's any possible workarounds that we could add upstream.

[brianhelba]

Note, in Python 3.12+, the strictly correct syntax is a bit less awkward (since TypeVar isn't needed):

  class MyModelViewSet(viewsets.ModelViewSet[MyModel]):
      @override
      def filter_queryset[MyModelRow](self, queryset: QuerySet[MyModel, MyModelRow]) -> QuerySet[MyModel, MyModelRow]:
          ...

I still don't think this is intuitive for most users.