Classes & Objects

Model real things in code with classes, attributes and methods — the heart of object-oriented programming.

🎯 What you will learn

Define a class with __init__
Create objects with their own attributes
Write methods that use self

👋 Let’s get started!

A class is a blueprint 📐; objects are the things built from it. One “Pet” class can create thousands of different pets, each with its own name and mood. This is object-oriented programming (OOP), used in almost every big app.

🪜 Step by step

1. 📐 Blueprint

class defines the blueprint. __init__ runs when an object is created.

class Pet:
    def __init__(self, name, species):
        self.name = name
        self.species = species

2. 🐶 Objects

Call the class like a function to build objects.

rex = Pet("Rex", "dog")
mia = Pet("Mia", "cat")
print(rex.name, mia.species)

3. ⚙️ Methods

Methods are functions inside a class. self means “this object”.

class Pet:
    def __init__(self, name):
        self.name = name
        self.hunger = 5

    def feed(self):
        self.hunger -= 2
        print(f"{self.name} munches. Hunger: {self.hunger}")

🧪 Try it!

Change the code and press ▶ Run to see what happens. You can’t break anything!

Virtual pet

class Pet:
    def __init__(self, name):
        self.name = name
        self.happiness = 5

    def play(self):
        self.happiness += 2
        return f"{self.name} chases the ball! 😄 ({self.happiness})"

    def __str__(self):
        return f"Pet {self.name} with happiness {self.happiness}"

buddy = Pet("Buddy")
print(buddy.play())
print(buddy.play())
print(buddy)

Build a BankAccount class

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

📖 Key words

Tap a card to flip it over!

Class: A blueprint for objects 📐
Object: A thing built from a class 🧱
Attribute: Data stored in an object 🏷️
self: The current object 🪞

🏆 Challenge

Finish the Rectangle class so area() returns width × height. The program should print 12.

Challenge

class Rectangle:
    def __init__(self, width, height):
        self.width = width
        self.height = height

    def area(self):
        pass

print(Rectangle(3, 4).area())

Knowledge Check Quiz

What does __init__ do?
What prints?
A class is like a…