Python - Polymorphism

As explained in our previous article, the procedure of overriding the definition of a method of a class(being inherited) in its subclass is known as method overriding. This leads to an important concept - Polymorphism.

Polymorphism means having many forms, and in Python it means having different forms/versions of a method(with the same name) in different classes by method overriding.

Doing this, allows a programming structure such as a loop or function or a method to use the objects of a base class or its derived class, to call the forms of overridden method without having to worry about the actual type of object.

Now, which specific form of the overridden method is executed is determined at the runtime, that is based on the type of the object used to make the method call.

Don't worry if you have not got it yet, let us make it easy for you through an example of Polymorphism.

Example of Polymorphism

# Python - Polymorphism in Python

# Base class
class Fruit:			
    def message(self):
        print('Eat Fruits')



# Derived class
class Apple(Fruit)
    
    # method message() of base class Fruit is overridden 
    def message(self):
        print('Eat Apples')



# Creating an object of Fruit
ob_fruit = Fruit()


# Creating an object of Apple
ob_apple = Apple()



# Creating a list of objects
a_list = [ob_fruit, ob_apple, ob_apple, ob_fruit]



# Using a for loop to iterate through a list of objects in list i.e.  a_list
for ob in a_list:
    ob.message()

Output

Eat Fruits
Eat Apples
Eat Apples
Eat Fruits

Program Analysis

Fruit

message()

Apple

Next, we have created a list of objects of class Fruit and Apple and have iterated through it by using a for loop, where on each iteration, we have called the overridden method message().
The definition of the overridden method message() to be invoked at the runtime is based on the type of the object that has called it.
The class Fruit and Apple can also be termed as polymorphic classes.

A function accessing the polymorphic classes

# Base class
class Sports:			
    def play(self):
        print('Play Sports')




# Derived class
class Football(Sports):
    
    # method message() of base class Sports is overridden 
    def play(self):
        print('Play Football')


# Derived class
class Tennis(Sports):
    
    # method message() of base class Sports is overridden 
    def play(self):
        print('Play Tennis')



# A function misc() which will be passed a list of mixed objects
def misc(l):
    for ob in l:
        ob.play()
    


# Creating an object of Sports
ob_sports = Sports()


# Creating an object of Football
ob_football = Football()


# Creating an object of Tennis
ob_tennis = Tennis()


# Creating a list of objects
a_list = [ob_sports, ob_football, ob_tennis]


# Calling misc() function with a list of mixed objects i.e. a_list
misc(a_list)

Output

Play Sports
Play Football
Play Tennis

Program Analysis

In the example above, we have created a class named Sports, which is inherited and its method play() is overridden in its subclasses, Football and Tennis.
Next, we have created a list of objects of these classes and have passed it to the general function misc(), which is not part of either of these classes.
The function misc() iterates through the list of objects by using a for loop, where on each iteration, it calls the overridden method play().
The definition of the overridden method play() to be invoked at the runtime is based on the type of the object that has called it.

A class method accessing the polymorphic classes

# Base class
class Sports:			
    def play(self):
        print('Play Sports')





# Derived class
class Football(Sports):
    
    # method message() of base class Sports is overridden 
    def play(self):
        print('Play Football')



class Misc:
    # A function misc() which will be passed a list of mixed objects
    # Depending on the type of objects, its associated method will be called
    def misc(self, l):
        for ob in l:
            ob.play()






# Creating an object of Sports
ob_sports = Sports()


# Creating an object of Football
ob_football = Football()



# Creating a list of objects
a_list = [ob_sports, ob_football]



# Creating an object of Misc
ob_misc = Misc()


# Calling misc() function with a list of mixed objects i.e. a_list
ob_misc.misc(a_list)

Output

Play Sports
Play Football
Play Tennis

Program Analysis

In the example above, we have created a class named Sports, which is inherited and its method play() is overridden in its subclass, Football.
Next, we have created a list of objects of classes these classes and have passed it to the general function misc(), which belongs to a non-polymorphic class Misc.
The function iterates through the list of objects by using a for loop, where on each iteration, it calls the overridden method play().
The definition of the overridden method play() to be invoked at the runtime is based on the type of the object that has called it.