So far, you’ve written Python programs using variables, functions, loops, and lists this is called procedural programming.

But what if you want to:

• Represent real-world things like a Car, Student, or Book?
• Reuse and organize your code better?
• Build scalable applications like games, dashboards, or web APIs?

That’s where Object-Oriented Programming (OOP) comes in.

In this post, we’ll cover:

• What OOP is and why it matters
• How to create and use classes and objects
  🔗 Read this detailed explanation of classes and objects in a dedicated post →
• Instance variables vs methods
  🔗 Read this detailed explanation of Instance variables vs methods in a dedicated post →
• What is self in Python?
  🔗 Read this detailed explanation of self in a dedicated post →
• Constructors (__init__)
• A real-world example
• Best practices and common mistakes

Let’s dive in.

🧠 What Is Object-Oriented Programming?

Object-Oriented Programming (OOP) is a way of writing programs using objects that combine:

• Data (variables like name, age, balance)
• Behavior (functions like withdraw, display, speak)

Think of it as creating your own custom data types.

🧱 What Is a Class?

A class is a blueprint for creating objects.

class Student:
    pass

🧍‍♂️ What Is an Object?

An object is an instance of a class it’s the actual thing based on the blueprint.

s1 = Student()  # s1 is an object of the Student class

🔧 __init__ Method – The Constructor

Let’s create a more useful class:

class Student:
    def __init__(self, name, age):
        self.name = name
        self.age = age

🔍 Breakdown:

• __init__() is a special method that runs when you create an object
• self refers to the object being created
• name and age are input parameters
• self.name creates a variable tied to the object

✅ Creating Objects from Class

s1 = Student("Ali", 20)
s2 = Student("Fatima", 22)

print(s1.name)   # Ali
print(s2.age)    # 22

🎯 What is self in Python?

Think of self as:

• A label that refers to the current object
• Required as the first argument in all class methods
• Automatically passed when you call methods on the object

class Example:
    def say_hello(self):
        print("Hello!")

e = Example()
e.say_hello()  # No need to pass 'self' Python does that

🔁 Adding Methods (Functions Inside Classes)

class Student:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    def speak(self):
        print(f"My name is {self.name}, and I'm {self.age} years old.")

s1 = Student("Ali", 21)
s1.speak()  # My name is Ali, and I'm 21 years old.

🎯 Class vs Instance Variables

Class Variable: Shared across all objects

Instance Variable: Unique per object

class Student:
    school = "PyUniverse"  # Class variable
    
    def __init__(self, name):
        self.name = name    # Instance variable

💡 Real-Life OOP Example: Bank Account

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

    def deposit(self, amount):
        self.balance += amount
        print(f"₹{amount} deposited. New balance: ₹{self.balance}")

    def withdraw(self, amount):
        if amount > self.balance:
            print("Insufficient funds.")
        else:
            self.balance -= amount
            print(f"₹{amount} withdrawn. Remaining balance: ₹{self.balance}")

a1 = BankAccount("Sufiyan", 1000)
a1.deposit(500)
a1.withdraw(700)

🔁 Using __str__ to Print Objects Nicely

class Product:
    def __init__(self, name, price):
        self.name = name
        self.price = price
    
    def __str__(self):
        return f"{self.name} costs ₹{self.price}"

p = Product("Keyboard", 899)
print(p)  # Keyboard costs ₹899

⚠️ Common OOP Mistakes (and Fixes)

More To Read On This Topic

• Encapsulation in Python: Data Hiding, __str__(), and Clean Class Design
• Learn Python Programming from Scratch: A Beginner’s Roadmap