[Python] Mypy error, [Type] has no attribute [method]

I have an abstract base class:

import abc
import typing as t

class Parent1(abc.ABC):
...


And a subclass of that abstract base class above, that is itself an abstract base class:

class Parent2(Parent1):

@abc.abstractmethod
def method2(self) -> None:
...



And now a concrete child class that inherits from Parent2 abstract class:

class Child1(Parent2):

def method2(self) -> None:
pass


And another concrete child class that inherits from Parent1 class:

class Child2(Parent1):
pass


Now I'm trying to make a generic container to holds all instances of Parent1 class

T = t.TypeVar("T")

class Container(t.Generic[T]):

def __init__(self) -> None:
self._containers: t.Dict[str, T] = {}

def add_item(self, name: str, item: T) -> None:
# reveal_type(item)
self._containers[name] = item

def get_item(self, name: str) -> T:
return self._containers[name]


container: Container[Parent1] = Container()

container.add_item("child1", Child1())
container.add_item("child2", Child2())


child1 = container.get_item("child1")
# assert isinstance(child1, Child1)
# reveal_type(child1) # Revealed type is "generic1.Parent1"

child1.method2()
# t.cast(Child1, child1).method1()


When trying to run mypy --strict without assert isinstance or cast, it report an error saying that error: "Parent1" has no attribute "method2"

How to fix the problem without using assert isinstance or typing.cast, or even without the # type: ignore comment?

Continue reading...