Question: How to bound a mixin to a subclass #8705
Description
I created a mixin for Django models and I would like to know how to properly type it, e.g.:
from django.db import models T = TypeVar("T", bound=models.Model) class SafeCreateMixin: @classmethod @transaction.atomic() def safe_create(cls: Type[T], **kwargs) -> Optional[T]: try: return cls.objects.create(**kwargs) except IntegrityError as e: return None class MyModel(SafeCreateMixin, models.Model): ....It fails with the following error:
error: The erased type of self "Type[django.db.models.base.Model]" is not a supertype of its class "Type[SafeCreateMixin]" I understood that the mypy docs recommend creating a Protocol for mixins, but in my case, I just want to enforce that my mixins are added to a subclass of models.Model