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Lesson 13: Python Classes and Object-Oriented Programming (OOP) | Coding Class Series

Introduction

Welcome to Lesson 13!
In this lesson, we will learn about Object-Oriented Programming (OOP) in Python, including classes, objects, methods, and inheritance.
OOP helps you structure your code in a way that models real-world objects and makes programming more organized and reusable.

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1. What is a Class?

A class is a blueprint for creating objects. It defines attributes (data) and methods (functions).

# Define a class
class Dog:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    def bark(self):
        print(f"{self.name} says Woof!")

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2. Creating Objects

An object is an instance of a class.

# Create objects
dog1 = Dog("Buddy", 3)
dog2 = Dog("Max", 5)

print(dog1.name)  # Buddy
dog2.bark()       # Max says Woof!

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3. The __init__ Method

• __init__ is a constructor used to initialize objects.
• self refers to the instance of the class.

class Cat:
    def __init__(self, name, color):
        self.name = name
        self.color = color
    
    def meow(self):
        print(f"{self.name}, the {self.color} cat, says Meow!")

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4. Methods

Methods are functions inside classes that operate on objects.

class Circle:
    def __init__(self, radius):
        self.radius = radius
    
    def area(self):
        return 3.1416 * self.radius ** 2
    
    def perimeter(self):
        return 2 * 3.1416 * self.radius

c = Circle(5)
print(c.area())       # 78.54
print(c.perimeter())  # 31.416

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5. Inheritance

Inheritance allows a class to inherit attributes and methods from another class.

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

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

class Cat(Animal):
    def speak(self):
        print("Meow Meow")

d = Dog()
c = Cat()
d.speak()  # Woof Woof
c.speak()  # Meow Meow

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6. Encapsulation

Encapsulation hides data inside a class using private attributes.

class BankAccount:
    def __init__(self, balance):
        self.__balance = balance  # private variable
    
    def deposit(self, amount):
        self.__balance += amount
    
    def get_balance(self):
        return self.__balance

account = BankAccount(1000)
account.deposit(500)
print(account.get_balance())  # 1500

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7. Polymorphism

Polymorphism allows objects of different classes to be used interchangeably.

class Bird:
    def speak(self):
        print("Tweet")

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

def make_speak(animal):
    animal.speak()

b = Bird()
d = Dog()
make_speak(b)  # Tweet
make_speak(d)  # Woof

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8. Practice Exercises

1. Create a class Student with attributes name, roll_no, marks. Write a method to calculate percentage.
2. Create a class Vehicle and inherit it with Car and Bike. Add different methods to each.
3. Implement encapsulation for a Library class where books is private.
4. Write a program demonstrating polymorphism with two different classes.

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