Assignment error on serializer fields named as Field properties

[oystein-beaufort]

When some of the fields in a ModelSerializer (but probably any serializer) has the same name as the annotated properties of the class Field in rest_framework-stubs.fields.pyi, e.g. source, required, etc., mypy raises an assignment error.

Example:

class MatchSerializer(serializers.ModelSerializer):
    source = MatchSourceSerializer()
    ...

This results in the following mypy error:

Incompatible types in assignment (expression has type "MatchSourceSerializer", base class "Field" defined the type as "Union[Callable[..., Any], str, None]")

If I change the type of source in fields.pyi like this:

class Field(Generic[_VT, _DT, _RP, _IN]):
    ...
    source: Literal["example"]  # Optional[Union[Callable, str]]
    ...

mypy now raises the following error

Incompatible types in assignment (expression has type "MatchSourceSerializer", base class "Field" defined the type as "Literal['example']")

System information

• OS: MacOS Big Sur 11.2.3
• python version: 3.7
• django version: 3.1.12
• djangorestframework version: 3.12.2
• mypy version: 0.812
• django-stubs version: 1.8.0
• djangorestframework-stubs version: 1.4.0

NOTE: This is similar to https://github.com/typeddjango/djangorestframework-stubs/issues/78, but not the same issue

[hongquan]

Any workaround for this issue?

[oystein-beaufort]

Current workaround: # type: ignore ;)