get_serializer_context() return type should be dict, not Mapping

[Alexerson]

Bug report

What's wrong

GenericAPIView.get_serializer_context() is typed as returning Mapping[str, Any], which causes a type error when subclasses follow the common Django REST Framework pattern of calling super() and then adding keys to the returned context:

def get_serializer_context(self):
    context = super().get_serializer_context()
    context['new_key'] = True  # Error here
    return context

mypy reports:

Unsupported target for indexed assignment ("Mapping[str, Any]")  [index]

Mapping is read-only by design, so typed assignment to its keys is not allowed. Since get_serializer_context() implementations actually return a plain mutable dict, the return type should reflect that.

How is that should be

get_serializer_context() should be typed as returning dict[str, Any] instead of Mapping[str, Any]. This matches the actual runtime return type and allows callers to mutate the context without needing a dict() cast or cast()
call:

def get_serializer_context(self):
    context = super().get_serializer_context()  # dict[str, Any]
    context['new_key'] = True  # No error
    return context

Note: accepting a Mapping type as input to serializer context= is a separate and reasonable change (see #636), but the return type of get_serializer_context() should remain dict.

System information

• OS: Linux 7.0.5
• python version: 3.14.4
• django version: 6.0.5
• mypy version: 1.20.0
• django-stubs version: 6.0.4

[terencehonles]

I also ran into this issue and allowed the serializer to capture the value passed in so it can be more tightly typed with #986

[bvedad]

I am facing the same issue.