Method Overriding in Python (original) (raw)

Method overriding is an ability of any object-oriented programming language that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its super-classes or parent classes. When a method in a subclass has the same name, the same parameters or signature, and same return type(or sub-type) as a method in its super-class, then the method in the subclass is said to **override the method in the super-class.

**Prerequisite: Inheritance in Python

overriding-in-python

The version of a method that is executed will be determined by the object that is used to invoke it. If an object of a parent class is used to invoke the method, then the version in the parent class will be executed, but if an object of the subclass is used to invoke the method, then the version in the child class will be executed. In other words, it is the type of the object being referred to (not the type of the reference variable) that determines which version of an overridden method will be executed.

**Example:

super().__init__(): This ensures that the parent class's constructor is called, initializing any attributes defined in the parent class. It’s good practice to call the parent class constructor if it does important initialization.
**Method Override: The Child class overrides the show() method of the Parent class, so when show() is called on an instance of Child, it uses the Child class’s implementation. Python `

Python program to demonstrate

Defining parent class

class Parent():

# Constructor 
def __init__(self): 
    self.value = "Inside Parent"
    
# Parent's show method 
def show(self): 
    print(self.value)

Defining child class

class Child(Parent):

# Constructor 
def __init__(self): 
    super().__init__()  # Call parent constructor
    self.value = "Inside Child"
    
# Child's show method 
def show(self): 
    print(self.value)

Driver's code

obj1 = Parent() obj2 = Child()

obj1.show() # Should print "Inside Parent" obj2.show() # Should print "Inside Child"

**Output:

Inside Parent
Inside Child

Method overriding with multiple and multilevel inheritance

**Multiple Inheritance: When a class is derived from more than one base class it is called multiple Inheritance.

**Example: Let's consider an example where we want to override a method of one parent class only.

Python `

Python program to demonstrate

Defining parent class 1

class Parent1():

# Parent's show method 
def show(self): 
    print("Inside Parent1")

Defining Parent class 2

class Parent2():

# Parent's show method 
def display(self): 
    print("Inside Parent2")

Defining child class

class Child(Parent1, Parent2):

# Child's show method 
def show(self): 
    print("Inside Child")

Driver's code

obj = Child()

obj.show() obj.display()

**Output:

Inside Child
Inside Parent2

**Multilevel Inheritance: When we have a child and grandchild relationship.

**Example: Let's consider an example where we want to override only one method of one of its parent classes.

Python `

Python program to demonstrate

overriding in multilevel inheritance

class Parent():

# Parent's show method 
def display(self): 
    print("Inside Parent")

Inherited or Sub class (Note Parent in bracket)

class Child(Parent):

# Child's show method 
def show(self): 
    print("Inside Child")

Inherited or Sub class (Note Child in bracket)

class GrandChild(Child):

# Child's show method 
def show(self): 
    print("Inside GrandChild")

Driver code

g = GrandChild() g.show() g.display()

**Output:

Inside GrandChild
Inside Parent

Calling the Parent's method within the overridden method

Parent class methods can also be called within the overridden methods. This can generally be achieved by two ways.

**Using Classname: Parent's class methods can be called by using the Parent classname.method inside the overridden method.

**Example:

Python `

Python program to demonstrate

calling the parent's class method

inside the overridden method

class Parent():

def show(self): 
    print("Inside Parent")

class Child(Parent):

def show(self): 
    
    # Calling the parent's class 
    # method 
    Parent.show(self) 
    print("Inside Child")

Driver's code

obj = Child() obj.show()

**Output:

Inside Parent
Inside Child

**Using Super()

Python super() function provides us the facility to refer to the parent class explicitly. It is basically useful where we have to call superclass functions. It returns the proxy object that allows us to refer parent class by ‘super’.

**Example 1:

Python `

Python program to demonstrate

calling the parent's class method

inside the overridden method using

super()

class Parent():

def show(self): 
    print("Inside Parent")

class Child(Parent):

def show(self): 
    
    # Calling the parent's class 
    # method 
    super().show() 
    print("Inside Child")

Driver's code

obj = Child() obj.show()

**Output:

Inside Parent
Inside Child

**Example 2:

Python `

Program to define the use of super()

function in multiple inheritance

class GFG1: def init(self): print('HEY !!!!!! GfG I am initialised(Class GEG1)')

def sub_GFG(self, b): 
    print('Printing from class GFG1:', b)

class GFG2 inherits the GFG1

class GFG2(GFG1): def init(self): print('HEY !!!!!! GfG I am initialised(Class GEG2)') super().init()

def sub_GFG(self, b): 
    print('Printing from class GFG2:', b) 
    super().sub_GFG(b + 1)

class GFG3 inherits the GFG1 ang GFG2 both

class GFG3(GFG2): def init(self): print('HEY !!!!!! GfG I am initialised(Class GEG3)') super().init()

def sub_GFG(self, b): 
    print('Printing from class GFG3:', b) 
    super().sub_GFG(b + 1)

main function

if name == 'main':

# created the object gfg 
gfg = GFG3() 

# calling the function sub_GFG3() from class GHG3 
# which inherits both GFG1 and GFG2 classes 
gfg.sub_GFG(10)

**Output:

HEY !!!!!! GfG I am initialised(Class GEG3)
HEY !!!!!! GfG I am initialised(Class GEG2)
HEY !!!!!! GfG I am initialised(Class GEG1)
Printing from class GFG3: 10
Printing from class GFG2: 11
Printing from class GFG1: 12