Python Class Inheritance

Inheritance is a way to form new classes using classes that have already been defined. The newly formed classes are called derived classes, the classes that we derive from are called base classes. Important benefits of inheritance are code reuse and reduction of complexity of a program. The derived classes (descendants) override or extend the functionality of base classes (ancestors).

class Animal:

    def __init__(self):
        print("Animal created")

    def whoAmI(self):
        print("Animal")

    def eat(self):
        print("Eating")


class Dog(Animal):

    def __init__(self):
        super().__init__()
        
        print("Dog created")

    def whoAmI(self):
        print("Dog")

    def bark(self):
        print("Woof!")

d = Dog()
d.whoAmI()
d.eat()
d.bark()

In this example, we have two classes: Animal and Dog. The Animal is the base class, the Dog is the derived class. The derived class inherits the functionality of the base class. It is shown by the eat method. The derived class modifies existing behavior of the base class, shown by the whoAmI method. Finally, the derived class extends the functionality of the base class, by defining a new bark method.

class Dog(Animal):
    def __init__(self):
        super().__init__()
        print("Dog created")

We put the ancestor classes in round brackets after the name of the descendant class. If the derived class provides its own __init__ method, and we want to call the parent constructor, we have to explicitly call the base class __init__ method with the help of the super function.

$ ./inherit.py 

Animal created
Dog created
Dog
Eating
Woof!