Purpose of polymorphism in Python - Step-by-Step Execution

Concept Flow - Purpose of polymorphism

Define base class

↓

Define subclasses

↓

Create objects of subclasses

↓

Call same method on each object

↓

Each object runs its own version

↓

Program uses objects interchangeably

Polymorphism lets different objects respond to the same method call in their own way, so code can work with many types easily.

Execution Sample

Python

class Animal:
    def speak(self):
        pass

class Dog(Animal):
    def speak(self):
        return "Woof!"

class Cat(Animal):
    def speak(self):
        return "Meow!"

animals = [Dog(), Cat()]
for animal in animals:
    print(animal.speak())

This code shows two animals speaking differently using the same method name.

Execution Table

Step	Action	Object	Method Called	Output
1	Create Dog object	Dog instance	-	-
2	Create Cat object	Cat instance	-	-
3	Call speak() on Dog	Dog instance	speak()	Woof!
4	Call speak() on Cat	Cat instance	speak()	Meow!
5	Loop ends	-	-	-

💡 All objects in list processed, loop ends

Variable Tracker

Variable	Start	After 1	After 2	Final
animals	[]	[Dog()]	[Dog(), Cat()]	[Dog(), Cat()]
animal	-	Dog()	Cat()	-

Key Moments - 2 Insights

Why does calling the same method speak() on different objects produce different outputs?

Each subclass (Dog, Cat) has its own speak() method. The program calls the method on the object’s actual class, so output differs (see execution_table steps 3 and 4).

Why can we put different animal objects in the same list and call speak() on all?

Because all objects share the same base class Animal and have a speak() method, the code treats them the same way, showing polymorphism (see variable_tracker for animals list).

Visual Quiz - 3 Questions

Look at the execution_table, what is the output when speak() is called on the Dog object?

A "Meow!"

B "Woof!"

C "speak()"

D No output

💡 Hint

Check execution_table row 3 where Dog's speak() is called

At which step does the program call speak() on the Cat object?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look at execution_table row 4 for Cat's speak() call

If we add a new class Bird with its own speak() method and add Bird() to animals, what changes in variable_tracker?

A animals list will be empty

B animal variable will only hold Dog() and Cat()

C animals list will include Bird() after Cat()

D No change in animals list

💡 Hint

variable_tracker shows animals list growing as objects are added

Concept Snapshot

Polymorphism means one method name works for many object types.
Each class defines its own version of the method.
Code calls the method on objects without knowing exact type.
This makes code flexible and easy to extend.
Example: animal.speak() calls Dog or Cat speak() automatically.

Full Transcript

Polymorphism allows different objects to respond to the same method call in their own way. In the example, Dog and Cat classes both have a speak() method. When we call speak() on a Dog object, it says "Woof!"; on a Cat object, it says "Meow!". We put these objects in a list and loop through them, calling speak() on each. The program automatically uses the right method for each object. This lets us write code that works with many types without changing it. The execution table shows each step: creating objects, calling speak(), and the outputs. The variable tracker shows how the animals list grows and which object is current. This is the purpose of polymorphism: to use one interface for many forms.