**Polymorphism** is a class property to modify superclass functionality. Methods or attributes can have various meanings and purposes inside the different classes. 
Methods in the superclass are **virtual**, that means they can be overridden in the children's classes.

## Code

Each class has the `say` method. But each method performs different things.

class Bird:
  def say(self):
    print('Chirp')

class Duck(Bird):
  def say(self):
    print('Quack')

class Rooster(Bird):
  def say(self):
    print('Cock-a-doodle-do')

bird = Bird() 
bird.say() 
duck = Duck() 
duck.say() 
rooster = Rooster()
rooster.say()

The first step is to understand the key statements. Classes, objects, attributes, methods...

Encapsulation provides access to the methods and attributes of the class.

Inheritance's main idea is to use already defined classes and produce new ones by improving and extending some other classes.

This OOP principle allows the user to change the parent class functionality and adapt it to the children's class.