Classes & Objects

Classes

A class is a blueprint. The __init__ method runs when you create an object, and self refers to the instance itself.

Basic Class

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

p1 = Person("Alice", 25)
print(p1.name, p1.age)

Methods

Methods are functions defined inside a class. They always take self as the first parameter.

class Rectangle:
    def __init__(self, width, height):
        self.width = width
        self.height = height

    def area(self):
        return self.width * self.height

    def perimeter(self):
        return 2 * (self.width + self.height)

r = Rectangle(4, 5)
print(r.area())
print(r.perimeter())

Class vs Instance Variables

Class variables are shared by all instances; instance variables belong to each object.

class Employee:
    company = "TechCorp"

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

e1 = Employee("Alice")
e2 = Employee("Bob")

print(e1.company, e1.name)
print(e2.company, e2.name)

Employee.company = "NewCorp"
print(e1.company)