Python 3 — OOP: Classes & Objects

🐍 Python 3 🟢 Lesson 14 📅 July 2026

Object-Oriented Programming (OOP) is a design pattern that models software after real-world objects. Instead of writing disconnected variables and functions, OOP binds them together inside a single, unified capsule called a Class.

1 Class Blueprints vs Object Instances

Think of a **Class** as a blueprint (like the architectural blueprint for a house). You can't live inside a blueprint. An **Object** is the actual house constructed from that blueprint. You can build as many houses as you want from a single blueprint!

2 Defining a Class & Constructor

We define classes using the class keyword. The __init__ function is the constructor method that initializes an object when it's created. The self parameter represents the current object instance:

Python 3 — Class Definition ▶ Run Code

class Student:
    # Constructor (Blueprint Setup)
    def __init__(self, name, score):
        self.name = name   # Attribute
        self.score = score # Attribute
        
    # Class Method (Action)
    def display_info(self):
        print(f"Student: {self.name}, Score: {self.score}/100")

# Constructing object instances
student1 = Student("Alice", 92)
student2 = Student("Balaji", 98)

# Running methods on instances
student1.display_info()
student2.display_info()

3 Modifying Object Attributes

You can access and modify attributes directly on object instances using the dot (.) syntax:

Python 3 — Modifying Objects ▶ Run Code

student1.score = 95 # Modify Alice's score
student1.display_info() # Student: Alice, Score: 95/100

💡 Understanding 'self':

The self parameter is mandatory inside class methods. When you call student1.display_info(), Python passes the student1 object as the first parameter (self) under the hood. This is how the method knows which object's attributes to display.

4 Coding Challenge

Create a class called 'Car' with constructor attributes for 'brand', 'model', and 'year'. Add a method called 'drive()' that prints: "[brand] [model] is driving away!". Instantiate a car object and call the method.