Classes and Objects in Python

In Object-Oriented Programming (OOP), a class is a blueprint for creating objects. An object is an instance of a class — it contains data (attributes) and behavior (methods).

Class vs Object

Term	Meaning
Class	Template or blueprint
Object	Instance of the class

How to Define a Class

class_syntax.py

class ClassName:
    def __init__(self, parameters):
        # attributes
        self.attribute = value
 
    def method(self):
        # method body
        pass

How to Create an Object

create_object.py

obj = ClassName(parameters)

Example 1: Simple Class with Method

example1_simple_class.py

class Animal:
    def sound(self):
        print("This animal makes a sound.")
 
a = Animal()
a.sound()

output.txt

This animal makes a sound.

Example 2: Class with Attributes

example2_attributes.py

class Dog:
    def __init__(self, name, breed):
        self.name = name
        self.breed = breed
 
    def info(self):
        print(f"My dog {self.name} is a {self.breed}.")
 
dog1 = Dog("Buddy", "Golden Retriever")
dog1.info()

output.txt

My dog Buddy is a Golden Retriever.

Example 3: Class with Multiple Methods

example3_multiple_methods.py

class Circle:
    def __init__(self, radius):
        self.radius = radius
 
    def area(self):
        return 3.1416 * self.radius * self.radius
 
    def perimeter(self):
        return 2 * 3.1416 * self.radius
 
c1 = Circle(5)
print("Area:", c1.area())
print("Perimeter:", c1.perimeter())

output.txt

Area: 78.54
Perimeter: 31.416

Example 4: Class with Default Attribute Values

example4_default_values.py

class Student:
    def __init__(self, name, grade="A"):
        self.name = name
        self.grade = grade
 
    def show(self):
        print(f"Student: {self.name}, Grade: {self.grade}")
 
s1 = Student("Alice")
s2 = Student("Bob", "B")
 
s1.show()
s2.show()

output.txt

Student: Alice, Grade: A
Student: Bob, Grade: B

Example 5: Class Representing Real-World Entity

example5_realworld.py

class BankAccount:
    def __init__(self, holder, balance):
        self.holder = holder
        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 show_balance(self):
        print(f"{self.holder}'s balance: ₹{self.balance}")
 
acc = BankAccount("John", 10000)
acc.deposit(2000)
acc.withdraw(1500)
acc.show_balance()

output.txt

John's balance: ₹10500

Summary

Class is a template — defines what attributes and methods an object will have.
Object is an instance — stores actual data.
You can define attributes using __init__().
You can define methods to operate on the object.
Objects allow you to model real-world entities in your programs.

In the next section, we will explore Constructors and __init__ — the special method used to initialize object state.

Introduction to OOP Constructors and `__init__`