Object-Oriented Programming – Classes

Defining classes, creating objects, instance variables, and methods.

What is a Class?

A class is a blueprint for creating objects. An object is an instance of a class containing both data (attributes) and behaviour (methods).

Defining a Class

class Dog:
    def __init__(self, name, breed):
        self.name = name
        self.breed = breed

    def bark(self):
        print(f"{self.name} says: Woof!")

    def __str__(self):
        return f"Dog({self.name}, {self.breed})"

rex = Dog("Rex", "German Shepherd")
rex.bark()
print(rex)

Class vs Instance Attributes

class Counter:
    count = 0   # class attribute (shared)

    def __init__(self):
        Counter.count += 1
        self.id = Counter.count   # instance attribute

a = Counter()
b = Counter()
print(Counter.count)  # 2

Methods

• Instance methods — take self as first parameter.
• Class methods — decorated with @classmethod, receive cls.
• Static methods — decorated with @staticmethod, receive neither.

class MathUtils:
    @staticmethod
    def is_even(n):
        return n % 2 == 0

print(MathUtils.is_even(4))  # True