Python Classes and Objects

Introduction

Classes and objects are the core of Object-Oriented Programming. A class defines a blueprint, while an object is a real instance created from it. This is how you build structured, reusable Python applications.

1. Creating a Basic Class

class Car:
    pass

mycar = Car()
print(mycar)

2. Adding Attributes (Constructor)

class Car:
    def __init__(self, model, year):
        self.model = model
        self.year = year

c = Car("Subaru Impreza", 2002)
print(c.model, c.year)

3. Adding Methods

class Car:
    def __init__(self, model):
        self.model = model

    def start(self):
        print(self.model, "is starting...")

car = Car("Impreza GX")
car.start()

4. The `self` Keyword

self refers to the current object and is required inside class methods.

5. Class Attributes vs Instance Attributes

class Player:
    max_hp = 100  # class attribute

    def __init__(self, name):
        self.name = name  # instance attribute

p1 = Player("Kal")
p2 = Player("Ghost")

print(Player.max_hp)
print(p1.name)

6. Inheritance

class Animal:
    def speak(self):
        print("Animal sound")

class Dog(Animal):
    def speak(self):
        print("Woof!")

d = Dog()
d.speak()

7. Method Overriding

Child classes can replace parent methods.

class Car:
    def drive(self):
        print("Car driving")

class Subaru(Car):
    def drive(self):
        print("Subaru with AWD driving!")

s = Subaru()
s.drive()

8. Using super()

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

class Student(Person):
    def __init__(self, name, grade):
        super().__init__(name)
        self.grade = grade

9. Magic Methods

Special methods that start and end with __.

class Vector:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __str__(self):
        return f"({self.x}, {self.y})"

v = Vector(5, 8)
print(v)

10. Encapsulation (Private Attributes)

class Bank:
    def __init__(self):
        self.__balance = 0

    def deposit(self, amt):
        self.__balance += amt

    def get_balance(self):
        return self.__balance

b = Bank()
b.deposit(100)
print(b.get_balance())

Summary