Abstract methods in Python3

You can use the Abstract Base Classes to implement abstract methods in Python. For example, if you have an Animal class and a Cat class like the following:

class Animal():
    def speak(self):
        print("Animal speak")

class Cat(Animal):
    pass

class Doc(Animal):
    pass

Cat().speak() # returns "Animal speak"
Dog().speak() # returns "Animal speak"

You can turn Animal.speak() to an abstract method with a metaclass and a decorator:

import abc

class Animal(metaclass=abc.ABCMeta):
    @abc.abstractmethod
    def speak(self):
        print("Animal speak")

class Cat(Animal):
    def speak(self):
        print("Cat speak")

class Dog(Animal):
    pass

Cat().speak() # returns "Cat speak"
Dog().speak() # returns "TypeError: Can't instantiate abstract class Dog with abstract methods speak"

Note that although the Animal.speak() method is always shadowed by its subclass method, it can still be called explicitly by using super():

class Cat(Animal):
    def speak(self):
        super().speak()

Cat().speak() # returns "Animal speak"