Polymorphism in Python

Learn how the same method or operation can behave differently for different objects.

What is Polymorphism?

Polymorphism is an important concept of Object-Oriented Programming.

The word polymorphism means "many forms".

In Python, the same method, function or operation can behave differently depending on the object or data being used.

Example 📩🌍

Think about the word "sound".

A dog makes one type of sound, while a cat makes another type of sound.

The method name can remain the same: sound(), but the behavior changes.

Polymorphism Diagram

Simple Example

class Dog:

    def sound(self):
        print("Dog barks")


class Cat:

    def sound(self):
        print("Cat meows")


dog1 = Dog()
cat1 = Cat()

dog1.sound()
cat1.sound()

Output:

Dog barks
Cat meows

Both classes have the same method name sound(), but the result is different.

Polymorphism through Method Overriding

When a child class provides its own version of a method that exists in the parent class, it is called method overriding.

class Animal:

    def sound(self):
        print("Animal makes a sound")


class Dog(Animal):

    def sound(self):
        print("Dog barks")


class Cat(Animal):

    def sound(self):
        print("Cat meows")


dog1 = Dog()
cat1 = Cat()

dog1.sound()
cat1.sound()

Output:

Dog barks
Cat meows

Same Interface, Different Behavior

We can call the same method on different objects.

animals = [Dog(), Cat()]

for animal in animals:
    animal.sound()

Output:

Dog barks
Cat meows

The loop does not need to know whether the object is a Dog or a Cat. Each object provides its own behavior for sound().

Polymorphism with Functions

A function can work with different objects as long as those objects provide the required method.

def make_sound(animal):
    animal.sound()


make_sound(Dog())
make_sound(Cat())

Output:

Dog barks
Cat meows

Polymorphism with Built-in Functions

Python's built-in functions can also behave differently depending on the object or data type.

Example: len()

print(len("Python"))
print(len([10, 20, 30, 40]))

Output:

6
4

The same len() function works with both a string and a list.

Operator Polymorphism

The same operator can behave differently depending on the data type.

print(10 + 20)

print("Hello " + "Python")

print([1, 2] + [3, 4])

Output:

30
Hello Python
[1, 2, 3, 4]

Here the + operator performs different operations for numbers, strings and lists.

Duck Typing

Python follows a concept called duck typing.

The important thing is what an object can do, rather than exactly what type of object it is.

class Dog:

    def sound(self):
        print("Bark")


class Cat:

    def sound(self):
        print("Meow")


def make_sound(animal):
    animal.sound()


make_sound(Dog())
make_sound(Cat())

Both objects have a sound() method, so the same function can work with both.

Bark
Meow

Different Forms of Polymorphism

Benefits of Polymorphism

• Makes code flexible.
• Reduces repeated code.
• Makes programs easier to extend.
• Allows common interfaces.
• Makes code easier to maintain.

Common Mistakes

• Using different method names when a common behavior is expected.
• Forgetting the self parameter.
• Calling a method that does not exist in the object.
• Confusing polymorphism with inheritance.

Practice Programs

1. Create Dog and Cat classes with a common sound() method.
2. Create a Vehicle class and override a method in child classes.
3. Create a function that works with two different objects.
4. Write examples of operator polymorphism.
5. Create a small duck typing example.