Overriding Methods in Child Classes in Python

Updated: at 03:12 AM

In object-oriented programming (OOP), inheritance allows a child class to inherit attributes and behaviors from a parent class. The child class can leverage the inherited features to expand its capabilities. One powerful technique is method overriding, which enables a child class to provide its own implementation for a method inherited from the parent class.

Proper use of method overriding is key to extending parent classes flexibly and creating maintainable code. This comprehensive guide will explain method overriding in detail with Python code examples. We will cover the following topics:

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What is Method Overriding

Method overriding is an OOP feature that allows a child class to provide its own implementation for a method already defined in its parent class.

The child class will inherit all the methods from the parent class. However, it can override specific inherited methods by redefining them using the same method signature. When the method is called on an instance of the child class, its overriding implementation will be executed instead of the parent’s version.

For example, consider a Animal parent class with a speak() method:

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

If we create a Dog child class that inherits from Animal, it will by default also have the speak() method:

class Dog(Animal):
  pass

dog = Dog()
dog.speak() # Outputs "The animal makes a sound"

However, we can override speak() in Dog to provide custom behavior:

class Dog(Animal):

  def speak(self):
    print("The dog barks woof!")

dog = Dog()
dog.speak() # Now outputs "The dog barks woof!"

So method overriding allows child classes to extend the parent’s capabilities by selectively modifying inherited behaviors.

Why Override Methods

There are several key reasons to override inherited methods:

Overall, overriding helps child classes refine and expand on parent class methods according to their specific needs. This makes inheritance more useful and flexible.

How to Override Methods in Python

Python makes overriding methods easy using the same method definition syntax as regular class methods:

class ChildClass(ParentClass):

  def overridden_method(self):
    # New implementation here

Let’s look at a complete example:

class Shape:

  def __init__(self, color):
    self.color = color

  def area(self):
    pass

class Square(Shape):

  def __init__(self, side_length, color):
    super().__init__(color)
    self.side = side_length

  def area(self):
    return self.side ** 2

class Circle(Shape):

  def __init__(self, radius, color):
    super().__init__(color)
    self.radius = radius

  def area(self):
    return 3.14 * (self.radius ** 2)

sq = Square(5, 'red')
print(sq.area()) # Outputs 25

cir = Circle(3, 'blue')
print(cir.area()) # Outputs 28.26

Using the super() Function

When overriding methods, it is often useful for the child class to access the parent’s implementation.

Python provides the super() function for this purpose. super() returns a proxy object bound to the parent class that allows us to call its methods.

For example, instead of duplicating the constructor logic in each child class, we can do:

class Shape:

  def __init__(self, color):
    self.color = color

class Square(Shape):

  def __init__(self, side_length, color):
    super().__init__(color) # Call parent constructor
    self.side = side_length

This invokes Shape’s __init__ method using super() to initialize the color attribute before setting the side specific to Square.

We can also leverage the parent’s implementation of a method while extending it in the child class:

class Shape:

  def log_sides(self):
    print("Shape has sides")

class Square(Shape):

  def log_sides(self):
    super().log_sides() # Call parent method
    print("Square has 4 sides")

So super() gives flexibility when overriding methods.

When to Use Method Overriding

Method overriding is useful in many scenarios, including:

However, method overriding should typically be avoided in some cases:

So like other OOP techniques, overriding should be applied judiciously where it simplifies code while enhancing extensibility.

Method Overriding vs Overloading

Overriding is often confused with overloading, another OOP concept for modifying class method behavior. But they differ in their approaches:

So with overriding, a subclass overrides a single parent method selectively. But overloading allows defining multiple variants of the same method in one class.

For example:

class Shape:

  def draw(self):
    # Parent draw method

class Circle(Shape):

  def draw(self):
    # Overrides parent draw() method

class Canvas:

  def draw(self):
    # Draw method #1

  def draw(self, shape):
    # Draw method #2, overloaded

Circle.draw() demonstrates overriding whereas Canvas has two overloaded draw() methods.

Best Practices for Overriding

When overriding methods properly, it improves code reuse and maintainability. Here are some best practices to follow:

Adhering to these principles will help keep subclasses robust and interchangeable with their parents.

Conclusion

Method overriding is a fundamental technique in OOP and Python for customizing inherited behavior. It enables subclasses to extend superclass capabilities according to specific needs while reusing common logic and structure through inheritance.

Following Python’s method definition syntax makes overriding straightforward. The super() function can also be leveraged to access inherited implementations. Overriding when applied properly helps improve polymorphism, abstraction, and code reuse.

This guide covered the key concepts and applications of method overriding in depth. The examples and best practices discussed should help you override methods effectively for building maintainable class hierarchies.