Suppose I have a Car class with the properties color and owner. Thinking from a seller's perspective, a new car doesn't have an owner yet. Therefore I'd like to make owner optional, as with the following code: from dataclasses import dataclass from enum import Enum class Color(Enum): RED = 0 BLUE = 1 @dataclass class Person(): name: str license_id: int class Car(): def __init__(self, color: Color, owner: Person|None = None) -> None: self.color: Color = color self.owner: Person|None = owner def sell_to(self, buyer: Person) -> None: self.owner = buyer Now when I try to sell this car to someone ... if __name__ == "__main__": new_car = Car(Color.RED) john_doe = Person("John Doe", 123) new_car.sell_to(john_doe) print(f"Car sold to {new_car.owner.name}") my language server (Pylance in VSCode) complains for new_car.owner.name that "name" is not a known attribute of "None", despite the code printing the correct output. When instead of using the type-hints Person|None I only use Person, Pylance complains in the init-definition that Expression of type "None" cannot be assigned to parameter of type "owner_type" and "None" is not assignable to "Person" How can I correctly type-hint the owner such that it is an optional property and I don't need to check if new_car.owner is not None every time I want to access that property? Continue reading...
