Functions and Objects · Objects · lesson 8 of 10

Inheritance

about 15 minutes · free · runs in your browser

Building on another class

A class can start from an existing one and change only what differs:

class Animal:
    def __init__(self, name):
        self.name = name

    def speak(self):
        return "..."

class Dog(Animal):
    def speak(self):
        return "Woof"

Dog inherits __init__ from Animal and overrides speak.

When a subclass needs its own __init__ as well, super() calls the parent's version so you do not repeat its work:

class Cat(Animal):
    def __init__(self, name, indoor):
        super().__init__(name)
        self.indoor = indoor

Inheritance is worth reaching for when the child genuinely is a kind of the parent. When you only want to reuse some code, a plain function or holding an instance as an attribute is usually the better tool.

Your turn: Shape is written for you. Add Circle and Rectangle, each with its own area().

You start from this, and edit it in the browser:

class Shape:
    def __init__(self, name):
        self.name = name

    def area(self):
        return 0


class Circle(Shape):
    def __init__(self, radius):
        # Call super().__init__ with the name "circle", then store the radius.
        pass

    def area(self):
        pass


class Rectangle(Shape):
    def __init__(self, width, height):
        pass

    def area(self):
        pass