Inheritance & Overriding

Inheritance

In object-oriented programming (OOP), inheritance is a mechanism that allows one class (called the subclass or derived class) to inherit the properties and behaviors of another class (called the superclass or base class). Inheritance is a key concept in OOP that facilitates code reuse and promotes the creation of a hierarchical structure for organizing and modeling software.

“When I see a bird that walks like a duck and swims like a duck and quacks like a duck, I call that bird a duck.”

James Whitcomb Riley It is not always required or even recommended to use inheritance, unless you are 100% sure you are required to do so.

Key Concepts of Inheritance

Base Class (Superclass): The class whose properties and behaviors are inherited by another class.

Derived Class (Subclass): The class that inherits from another class.

Method Overriding: The ability of a subclass to provide a specific implementation for a method that is already defined in its superclass.

Code Reusability: Inheritance promotes the reuse of code by allowing common functionality to be defined in a base class and shared among multiple subclasses.

Hierarchy: Inheritance enables the creation of a hierarchical structure of classes, where more specialized classes inherit from more general ones.

Example Inheritance Code

# Inheriting Vehicle
class Vehicle:
    def __init__(self, make, model, year):
        self.make = make
        self.model = model
        self.year = year

    def display_info(self):
        print(f"{self.year} {self.make} {self.model}")

class Car(Vehicle):
    def __init__(self, make, model, year, num_doors):
        super().__init__(make, model, year)
        self.num_doors = num_doors

    def display_info(self):
        super().display_info()
        print(f"Number of doors: {self.num_doors}")

# Example usage
my_vehicle = Vehicle("Toyota", "Camry", 2022)
my_vehicle.display_info()

my_car = Car("Ford", "Mustang", 2023, 2)
my_car.display_info()

# Output
Toyota Camry 2022
Ford Mustang 2023
Number of doors: 2

• Vehicle is the base class with common attributes like make, model, and year, as well as a method display_info to display information about the vehicle.

• Car is a subclass of Vehicle. It inherits the attributes from Vehicle using super().__init__(make, model, year), and it also has an additional attribute num_doors specific to cars. The display_info method is overridden to include information about the number of doors.

super() method

"Return a proxy object that delegates method calls to a parent or sibling class of type. This is useful for accessing inherited methods that have been overridden in a class."

- Python Documentation

super() in Python is a built-in function that is used to call a method from a parent class. It is often used in the context of inheritance to invoke a method or constructor from the parent class. This allows you to extend or override functionality in the child class while still reusing code from the parent class.

By using super(), you make your code more maintainable and allow for changes in the base class without having to update the derived classes manually.

In our example code, super().__init__(make, model, year) is used to call the constructor (__init__ method) of the parent class (Vehicle).

This ensures that the make, model, and year attributes are initialized in the Car instance, leveraging the initialization logic from the Vehicle class.

Overriding (Polymorphism)

Overriding occurs when two methods with the same method name and parameters within different classes. Overriding is a fundamental concept that shows polymorphism being evident in OOP.

Here are some scenarios when overriding occurs.

class Vehicle:
    def __init__(self, make, model, year):
        self.make = make
        self.model = model
        self.year = year

    def display_info(self):
        print(f"{self.year} {self.make} {self.model}")

class Car(Vehicle):
    def __init__(self, make, model, year, num_doors):
        super().__init__(make, model, year)
        self.num_doors = num_doors

    def display_info(self):
        super().display_info()
        print(f"Number of doors: {self.num_doors}")

There are two classes here:

1. A parent class called Vehicle

2. A child class called Car

Both Classes have the methods: display_info()

The method has the same parameters

The method behaves differently in each class; therefore, the child class is overriding the behaviour from the parent class.

You can also override built-in magic-methods/built-in base methods from python standard library.