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.

Practice

1. What is the main purpose of polymorphism in Python programming?

easy

A. To allow one function or method to work in different ways depending on the object

B. To make the program run faster by using multiple processors

C. To store multiple values in a single variable

D. To create a new data type from existing types

Solution

1. Step 1: Understand the meaning of polymorphism

   Polymorphism means one action can behave differently depending on the object it is acting on.

2. Step 2: Match the purpose with the options

   To allow one function or method to work in different ways depending on the object correctly describes this behavior, while others describe unrelated concepts.

3. Final Answer:

   To allow one function or method to work in different ways depending on the object -> Option A

4. Quick Check:

   Polymorphism = One action, many behaviors [OK]

Hint: Polymorphism means same name, different actions [OK]

Common Mistakes:

• Confusing polymorphism with speed optimization
• Thinking polymorphism is about storing multiple values
• Mixing polymorphism with data type creation

2. Which of the following is the correct way to demonstrate polymorphism with methods in Python?

easy

A. Define multiple methods with different names in the same class

B. Define methods with the same name in different classes and call them on their objects

C. Use only one method in one class without overriding

D. Use global variables to change method behavior

Solution

1. Step 1: Recall how polymorphism works with methods

   Polymorphism allows methods with the same name to behave differently in different classes.

2. Step 2: Check which option matches this behavior

   Define methods with the same name in different classes and call them on their objects correctly describes defining same-named methods in different classes and calling them on their objects.

3. Final Answer:

   Define methods with the same name in different classes and call them on their objects -> Option B

4. Quick Check:

   Same method name, different classes = polymorphism [OK]

Hint: Same method name in different classes shows polymorphism [OK]

Common Mistakes:

• Thinking polymorphism means different method names
• Ignoring method overriding in subclasses
• Using global variables to control method behavior

3. What will be the output of the following code?

class Dog:
    def sound(self):
        return "Bark"

class Cat:
    def sound(self):
        return "Meow"

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

medium

A. Meow
Bark

B. Bark
Bark

C. Error: sound method not found

D. Bark
Meow

Solution

1. Step 1: Understand the classes and their methods

   Dog and Cat classes both have a method named sound that returns different strings.

2. Step 2: Trace the loop calling sound on each object

   The loop calls sound() on Dog instance (returns "Bark") and Cat instance (returns "Meow"), printing each.

3. Final Answer:

   Bark Meow -> Option D

4. Quick Check:

   Different classes, same method name, different outputs [OK]

Hint: Same method name, different classes, different outputs [OK]

Common Mistakes:

• Assuming both calls return the same string
• Expecting a runtime error due to method name
• Mixing the order of outputs

4. Find the error in this code that tries to use polymorphism:

class Bird:
    def fly(self):
        print("Flying")

class Penguin(Bird):
    def fly(self):
        print("Cannot fly")

p = Penguin()
p.fly()

medium

A. No error; code correctly uses polymorphism

B. Penguin class must call super().fly() inside fly

C. Method fly must return a value

D. Penguin class should not override fly method

Solution

1. Step 1: Check method overriding in subclass

   Penguin overrides fly method to print "Cannot fly", which is valid polymorphism.

2. Step 2: Verify code execution

   Creating Penguin object and calling fly prints "Cannot fly" without error.

3. Final Answer:

   No error; code correctly uses polymorphism -> Option A

4. Quick Check:

   Overriding method in subclass is correct polymorphism [OK]

Hint: Overriding method in subclass is allowed [OK]

Common Mistakes:

• Thinking overriding is an error
• Expecting method must return a value
• Believing super() call is mandatory

5. You want to write a function that accepts any object and calls its draw() method, regardless of the object's class. Which concept does this best illustrate?

hard

A. Inheritance

B. Encapsulation

C. Polymorphism

D. Abstraction

Solution

1. Step 1: Understand the function requirement

   The function calls draw() on any object without knowing its class.

2. Step 2: Identify the concept allowing this behavior

   Polymorphism allows different objects to respond to the same method call appropriately.

3. Final Answer:

   Polymorphism -> Option C

4. Quick Check:

   Same method call, different objects = polymorphism [OK]

Hint: Calling same method on any object shows polymorphism [OK]

Common Mistakes:

• Confusing with inheritance which is about class hierarchy
• Mixing with encapsulation which hides data
• Thinking abstraction means calling any method