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Sameer Qaiser
Sameer Qaiser

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Python Classes: A Beginner's Guide to OOP

#python #beginners #oop #programming

📌 Quick Info

  • Topic: Classes and objects in Python
  • Target Audience: Beginners who know functions and dictionaries
  • Goal: Understand why classes exist and how to write one

1. Introduction

"For weeks, I stored everything in dictionaries. Then I had 10 players in a game, each with a name, score, and level — and I had to update all of them manually. That's when I learned about classes."

2. The Problem (Using Dictionaries for Everything) 

player1 = {"name": "Ali", "score": 0, "level": 1}
player2 = {"name": "Sara", "score": 0, "level": 1}
player3 = {"name": "Ahmed", "score": 0, "level": 1}

def add_score(player, points):
    player["score"] += points

add_score(player1, 10)
print(player1["score"])  # 10
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Problem: Every player is a plain dictionary. No structure. Easy to typo. Hard to scale.

3. The Solution (With Classes) 

lass Player:
    def _init_(self, name):
        self.name = name
        self.score = 0
        self.level = 1

    def add_score(self, points):
        self.score += points

player1 = Player("Ali")
player2 = Player("Sara")

player1.add_score(10)
print(player1.score)   
print(player2.score)
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Every Player is now a Player object with its own data and its own methods.

4. How It Works (Line By Line)

Line 1: class Player: — Defines a new class called Player.

Line 2: def init(self, name): — This runs automatically when you create a new player. It's called the constructor.

Line 3-5: self.name = name — Stores data on the object. self refers to the specific instance.

Line 7: def add_score(self, points): — A method that belongs to the class.

Line 11: player1 = Player("Ali") — Creates an instance (an object) of the class.

5. What is self?

self is how Python knows which player you're talking about.

When you write player1.add_score(10), Python translates it to:

Player.add_score(player1, 10)
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So self = player1 in that call. It's the object the method was called on.

Rule: Every method inside a class takes self as its first parameter. No exceptions.

6. Real Example (My Practice) 

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

    def deposit(self, amount):
        self.balance += amount

    def withdraw(self, amount):
        if amount > self.balance:
            print("Insufficient funds.")
        else:
            self.balance -= amount

    def show_balance(self):
        print(f"{self.owner}: ${self.balance}")

account = BankAccount("Ali", 100)
account.deposit(50)
account.withdraw(30)
account.show_balance()
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Output: 

Ali: $120
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7. Class vs Instance 

class Dog:
    species = "Canis familiaris"  

    def __init__(self, name):
        self.name = name          

dog1 = Dog("Rex")
dog2 = Dog("Max")

print(dog1.species)   
print(dog2.species)   
print(dog1.name)      
print(dog2.name)
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Class attribute = shared by every instance.
Instance attribute = unique to each instance.

8. What I learned

· Classes bundle data and behavior together
· —init— runs when you create a new instance
· Self is how methods know which instance they belong to
· Class attributes are shared, instance attributes are unique
· Classes make code easier to scale when you have many similar things

9. Conclusion

"Classes felt like overkill when I had one player. But when I had ten, they saved me hours. Now I reach for classes whenever I have multiple things with the same shape — because managing them manually is how bugs get born."

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