mypy-generics.py

from __future__ import annotations
from typing import Generic, TypeVar


T = TypeVar("T")

# ABC


class DatabaseProvider:
    pass


class StorageProvider:
    pass


class Connector(Generic[T]):
    def connect(self) -> T:
        pass


# Implementations

class GoogleProvider(DatabaseProvider, StorageProvider):
    pass


class GoogleConnector(Connector[GoogleProvider]):
    def connect(self) -> GoogleProvider:
        return GoogleProvider()


# Incompatible types in assignment (expression has type "GoogleConnector", variable has type "Connector[DatabaseProvider]")
_: Connector[DatabaseProvider] = GoogleConnector()