Python Classes & Objects – OOP Foundation Explained

Introduction – Why Use Classes and Objects in Python?

Python supports object-oriented programming (OOP), which organizes code into classes (blueprints) and objects (instances). This approach:

• Promotes reusability and modularity
• Makes code easier to manage
• Reflects real-world entities in your codebase

From web applications to data models and APIs, classes and objects are the building blocks of robust Python programs.

In this guide, you’ll learn:

• What classes and objects are in Python
• How to define and use them
• Special methods like __init__()
• Accessing and modifying object attributes
• Best practices and real-world examples

What Is a Class in Python?

A class is a blueprint for creating objects. It defines attributes (variables) and behaviors (methods) that the objects created from the class will have.

🧍 What Is an Object?

An object is an instance of a class. It holds actual values for the attributes defined in the class.

Defining a Class and Creating an Object

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

    def greet(self):
        return f"Hello, my name is {self.name} and I'm {self.age} years old."

Creating an Object

person1 = Person("Alice", 30)
print(person1.greet())

Output:

Hello, my name is Alice and I'm 30 years old.

Understanding __init__() Constructor

• __init__() is a constructor method
• Automatically called when a new object is created
• self refers to the current object

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

Object Attributes and Methods

Accessing Attributes

print(person1.name)  # Alice
print(person1.age)   # 30

Modifying Attributes

person1.age = 31
print(person1.greet())  # Updated age

Adding Attributes Dynamically

person1.city = "New York"
print(person1.city)  # New York

Multiple Objects from the Same Class

person2 = Person("Bob", 25)
print(person2.greet())  # Hello, my name is Bob and I'm 25 years old.

Each object has its own copy of data.

Class vs Instance Variables

class Product:
    tax = 0.1  # class variable

    def __init__(self, price):
        self.price = price  # instance variable

    def final_price(self):
        return self.price + (self.price * Product.tax)

Class Methods and Static Methods

class MyClass:
    @classmethod
    def class_info(cls):
        print("This is a class method.")

    @staticmethod
    def static_info():
        print("This is a static method.")

Real-World Example – Bank Account

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:
            self.balance -= amount
        else:
            print("Insufficient balance.")

    def get_balance(self):
        return self.balance

acc = BankAccount("Alice", 1000)
acc.deposit(500)
acc.withdraw(300)
print(acc.get_balance())  # 1200

Best Practices for Classes & Objects

Summary – Recap & Next Steps

Python’s classes and objects let you model real-world systems, organize code cleanly, and re-use logic effectively. With __init__(), attributes, methods, and instantiation, you can start building anything from APIs to simulations.

Key Takeaways:

• Classes define structure; objects are real instances
• Use __init__() to initialize object state
• Access and modify object attributes using dot notation
• Create multiple objects from the same class

Real-World Relevance:
Used in web development (Django, Flask), GUI apps, game design, machine learning models, and more.

FAQ – Python Classes & Objects

What’s the difference between a class and an object?

A class is a template; an object is an instance of that template with real data.

What is self in Python?

self refers to the current object. It’s required to access instance attributes and methods.

Can I create multiple objects from one class?

Yes. Each object will have its own data.

p1 = Person("A", 25)
p2 = Person("B", 30)

What’s the use of __init__()?

It initializes the object when it’s created. Think of it as a constructor.

Can I have optional parameters in a class?

Yes, just assign default values:

def __init__(self, name, age=18):
    ...