website/content/blog/pythonabstractclass.md

title	date	draft	tags
Quick Python: Abstract Classes	2020-01-26T18:40:03-05:00	false	python

You can create an abstract class in Python by inheriting Abstract Base Class (ABC) and declaring relevant methods abstract.

First import the following from the standard library,

from abc import ABC, abstractmethod

Then create an abstract class, making sure to add the decorator @abstractmethod to the constructor. This prevents the user from instantiating the class.

class Animal(ABC):
    @abstractmethod
    def __init__(self, name):
        self.name = name
    @abstractmethod
    def is_bipedal(self):
        pass
    def speak(self):
        return "Hello my name is " + self.name + " and I am a " + type(self).__name__

In the example above:

• A constructor is made, however, the class Animal cannot be instantiated. Do note that child classes can call the constructor.
• is_bipedal is an abstract method that needs to be defined in child classes. pass indicates that it is not implemented.
• speak is a normal method that will be inherited by child classes.

Now let's look at a class that inherits Animal.

class Dog(Animal):
    def __init__(self, name, owner):
        super().__init__(name) # Calls Animal constructor
        self.owner = owner
    def is_bipedal(self):
        return False