Inheritance in Python (46/100 Days of Python)

Day 46 of the “100 Days of Python” blog post series covering inheritance in Python classes

Inheritance is a fundamental concept in object-oriented programming (OOP) that allows you to create a new class that is a modified version of an existing class. The new class is called the derived class, and the existing class is called the base class. Inheritance enables you to reuse code and promote code reuse, making it easier to maintain and extend code.

In Python, inheritance works by defining a derived class that inherits from a base class. The derived class inherits all of the attributes and behaviors of the base class and can also add new attributes and behaviors, or override existing ones.

Defining a Base Class

To define a base class in Python, you use the class keyword and give the class a name. For example, the following code defines a base class called Animal:

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

    def make_sound(self):
        print('Some generic animal sound')

In this code, the Animal class has two attributes, name and species, and a method, make_sound, that prints a generic animal sound.

Defining a Derived Class

To define a derived class in Python, you create a new class and inherit from the base class using parentheses. For example, the following code defines a derived class called Dog that inherits from the Animal class:

class Dog(Animal):
    def __init__(self, name, breed):
        super().__init__(name, species='Dog')
        self.breed = breed

    def make_sound(self):
        print('Woof!')

Here, the Dog class has a new attribute, breed, and a new implementation of the make_sound method. The Dog class also calls the __init__ method of the Animal class to initialize the name and species attributes.

Notice that the __init__() function of the base class is called using the super() method. The super call in the __init__ function is used to call the __init__ method of the base class in a derived class. The super call is a convenient way to call the __init__ method of the base class without having to specify the name of the base class. An alternative to using the super() method, would’ve been to call the base class by name:

class Dog(Animal):
    def __init__(self, name, breed):
        Animal.__init__(self, name, species='Dog')
        self.breed = breed

    def make_sound(self):
        print('Woof!')

Note that here we specify both the name of the base class and explicitly pass the self parameter as an argument.

Using Inheritance

To use inheritance, you create objects from the derived class, just like you would create objects from any other class. For example, the following code creates a Dog object and calls its make_sound method:

dog = Dog('Loby', 'Labrador')
dog.make_sound()
print(dog.breed)     # Labrador
print(dog.species)   # Dog
print(dog.name)      # Loby

This code will output Woof!, indicating that the make_sound method of the Dog class has overridden the make_sound method of the Animal class.

What’s next?

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• Previous topic: What are Magic Methods in Python Classes?
• Next topic: Method Overriding in Python