Classes and Objects

The cornerstone of Object-Oriented Programming — bundling data and behaviour together into reusable blueprints.

"A class is a blueprint. An object is something built from that blueprint. Every car in a factory is a different object, but they all share the same design."

— ShurAI

The Problem Classes Solve

Imagine storing data about three students using plain variables:

python — messy without classes

student1_name  = "Riya"
student1_score = 92
student1_grade = "A"

student2_name  = "Arjun"
student2_score = 75
student2_grade = "B"

# Ten students? Forty variables. Chaos.

A class bundles the data and behaviour of a thing into one reusable unit:

python — clean with a class

class Student:
    pass   # empty class for now

# Create two objects from the same blueprint
s1 = Student()
s2 = Student()

# Give each object its own data
s1.name  = "Riya"
s1.score = 92

s2.name  = "Arjun"
s2.score = 75

print(s1.name, s1.score)   # Riya 92
print(s2.name, s2.score)   # Arjun 75

Class vs Object — The Blueprint Analogy

🛠️

Class = Blueprint

Defines the structure: what data and actions this type of thing has.
Exists once in your code.
Example: class Car:

🚗

Object = Instance

A specific thing built from the blueprint.
Can create thousands.
Example: my_car = Car()

A Proper Class with Data and Methods

python

class Dog:
    def __init__(self, name, breed):
        self.name  = name     # store data on the object
        self.breed = breed

    def bark(self):
        print(f"{self.name} says: Woof!")

    def describe(self):
        print(f"{self.name} is a {self.breed}")

# Create two Dog objects
dog1 = Dog("Bruno", "Labrador")
dog2 = Dog("Luna",  "Husky")

dog1.bark()        # Bruno says: Woof!
dog2.describe()    # Luna is a Husky
print(dog1.name)    # Bruno

Key Terms

Term	Meaning	Example
class	The blueprint definition	class Dog:
object / instance	A specific thing built from the class	dog1 = Dog(...)
attribute	Data stored on an object	dog1.name
method	A function that belongs to a class	dog1.bark()

Real Example — BankAccount Class

python

class BankAccount:
    def __init__(self, owner, balance=0):
        self.owner   = owner
        self.balance = balance

    def deposit(self, amount):
        self.balance += amount
        print(f"Deposited {amount}. Balance: {self.balance}")

    def withdraw(self, amount):
        if amount > self.balance:
            print("Insufficient funds!")
        else:
            self.balance -= amount
            print(f"Withdrew {amount}. Balance: {self.balance}")

acc = BankAccount("Riya", 1000)
acc.deposit(500)
acc.withdraw(200)
acc.withdraw(2000)

output

Deposited 500. Balance: 1500
Withdrew 200. Balance: 1300
Insufficient funds!

"OOP isn't about writing more code — it's about writing better-organised code. When a class models a real-world concept cleanly, the rest of the program almost writes itself."

— ShurAI

🧠 Quiz — Q1

What is a class in Python?

🧠 Quiz — Q2

What is the difference between a class and an object?

🧠 Quiz — Q3

How do you access the name attribute on an object called dog1?

🧠 Quiz — Q4

What is a method?