How to override a method in a derived class while calling the base class method in Python?

Introduction

This tutorial will guide you through the process of overriding methods in a derived class while still calling the base class method in Python. You'll learn the fundamentals of method overriding and explore practical techniques to enhance your Python programming skills.

Skills Graph

Overriding Methods in Python

In Python, method overriding is a fundamental concept in object-oriented programming (OOP). It allows a derived class to provide a specific implementation of a method that is already defined in its base class. This is a powerful feature that enables code reuse and polymorphism.

Understanding Method Overriding

When a derived class defines a method with the same name as a method in its base class, the method in the derived class overrides the method in the base class. This means that when you call the method on an instance of the derived class, the implementation in the derived class is used, rather than the implementation in the base class.

class BaseClass:
    def my_method(self):
        print("This is the base class method.")

class DerivedClass(BaseClass):
    def my_method(self):
        print("This is the overridden method in the derived class.")

base_obj = BaseClass()
base_obj.my_method()  ## Output: This is the base class method.

derived_obj = DerivedClass()
derived_obj.my_method()  ## Output: This is the overridden method in the derived class.

In the example above, the DerivedClass overrides the my_method() of the BaseClass.

Reasons for Method Overriding

There are several reasons why you might want to override a method in a derived class:

1. Customization: You can customize the behavior of a method to suit the specific needs of the derived class.
2. Specialization: You can provide a more specialized implementation of a method in the derived class.
3. Polymorphism: Method overriding enables polymorphism, which allows objects of different classes to be treated as objects of a common superclass.

By overriding methods, you can create a more flexible and extensible codebase, where derived classes can adapt the behavior of the base class to their specific requirements.

Calling the Base Class Method

In some cases, you may want to call the base class method from the overridden method in the derived class. This can be useful when you want to reuse the functionality of the base class method and build upon it in the derived class.

Using super() to Call the Base Class Method

To call the base class method from the overridden method in the derived class, you can use the super() function. The super() function returns a proxy object that allows you to access methods in the base class.

class BaseClass:
    def my_method(self):
        print("This is the base class method.")

class DerivedClass(BaseClass):
    def my_method(self):
        print("Calling the base class method...")
        super().my_method()
        print("Doing additional work in the derived class method.")

derived_obj = DerivedClass()
derived_obj.my_method()

Output:

Calling the base class method...
This is the base class method.
Doing additional work in the derived class method.

In the example above, the DerivedClass overrides the my_method() of the BaseClass, but it also calls the base class method using super().my_method(). This allows the derived class to extend the functionality of the base class method.

Calling Multiple Base Class Methods

If a derived class inherits from multiple base classes, you can call the methods of each base class using the super() function. The order in which you call the base class methods is important, as it determines the method resolution order (MRO).

class BaseClass1:
    def my_method(self):
        print("This is the method from BaseClass1.")

class BaseClass2:
    def my_method(self):
        print("This is the method from BaseClass2.")

class DerivedClass(BaseClass1, BaseClass2):
    def my_method(self):
        print("Calling the base class methods...")
        super().my_method()
        BaseClass2.my_method(self)

derived_obj = DerivedClass()
derived_obj.my_method()

Output:

Calling the base class methods...
This is the method from BaseClass1.
This is the method from BaseClass2.

In this example, the DerivedClass inherits from both BaseClass1 and BaseClass2. When my_method() is called on an instance of DerivedClass, it first calls the my_method() of BaseClass1 using super().my_method(), and then it calls the my_method() of BaseClass2 directly.

By understanding how to call the base class method from the overridden method in the derived class, you can create more flexible and reusable code in your Python applications.

Practical Overriding Techniques

In this section, we'll explore some practical techniques for overriding methods in Python, including use cases and examples.

Overriding Methods in Subclasses

One common use case for method overriding is when you have a base class that provides a general implementation of a method, and you want to customize the behavior in a specific subclass. This allows you to reuse the base class functionality while adding or modifying the implementation to suit the needs of the subclass.

class Animal:
    def make_sound(self):
        print("The animal makes a sound.")

class Dog(Animal):
    def make_sound(self):
        print("The dog barks.")

dog = Dog()
dog.make_sound()  ## Output: The dog barks.

In this example, the Dog class overrides the make_sound() method of the Animal class to provide a more specific implementation.

Overriding Methods in Mixins

Mixins are a way to add functionality to a class by inheriting from multiple base classes. Method overriding can be useful when working with mixins, as it allows you to customize the behavior of the mixin's methods.

class LoggingMixin:
    def log_message(self, message):
        print(f"Logging message: {message}")

class MyClass(LoggingMixin):
    def log_message(self, message):
        super().log_message(f"[MyClass] {message}")

my_obj = MyClass()
my_obj.log_message("Hello, world!")

Output:

Logging message: [MyClass] Hello, world!

In this example, the MyClass overrides the log_message() method of the LoggingMixin to add a prefix to the logged message.

Overriding Methods in Abstract Base Classes

Abstract base classes (ABCs) are a way to define a common interface for a group of related classes. Method overriding can be used in conjunction with ABCs to provide concrete implementations of the abstract methods.

from abc import ABC, abstractmethod

class AbstractBase(ABC):
    @abstractmethod
    def do_something(self):
        pass

class ConcreteClass(AbstractBase):
    def do_something(self):
        print("Implementing the abstract method in the concrete class.")

concrete_obj = ConcreteClass()
concrete_obj.do_something()

Output:

Implementing the abstract method in the concrete class.

In this example, the ConcreteClass overrides the do_something() method defined as an abstract method in the AbstractBase class.

By understanding these practical techniques for method overriding, you can write more flexible and extensible code in your Python applications.

Summary

In this Python tutorial, you've learned how to override methods in a derived class while calling the base class method. By understanding the concepts of method overriding and inheritance, you can write more flexible and maintainable Python code. Mastering these techniques will empower you to create more robust and customizable applications.