Composable types [python-ABC] - Typescript to Python field guide

composition.py

from abc import ABC, abstractmethod


class Animal(ABC):
    @property
    @abstractmethod
    def length(self) -> float:
        ...

    @abstractmethod
    def eat(self, food: str) -> None:
        ...


class Fish(Animal):
    @abstractmethod
    def swim(self, howLong: float) -> None:
        ...


# MyFish explicitly implements the Fish interface
class MyFish(Fish):
    @property
    def length(self) -> float:
        return 12

    def eat(self, food: str) -> None:
        print(f"Eating {food}")

    def swim(self, howLong: float) -> None:
        print(f"Swimming for {howLong}")


fish = MyFish()


def do_something_fishy(what: Fish):
    what.eat("worms")
    what.swim(what.length)


do_something_fishy(fish)  # this is ok!