Object-Oriented Programming in Python

1. What is a Class?

A class is a blueprint for creating objects. Each object created from a class is called an instance, containing its own data and methods.

Creating a Class

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

    def bark(self):
        return "Woof!"

Here, Dog is a class with an initializer method __init__ and a method bark(). The self parameter refers to the instance.

Creating an Instance

dog1 = Dog("Buddy", 3)
print(dog1.name)  # Output: Buddy
print(dog1.bark())  # Output: Woof!

2. Inheritance

Inheritance allows a class to inherit attributes and methods from another class, promoting code reuse and creating a hierarchy of classes.

Example of Inheritance

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

class Dog(Animal):
    def bark(self):
        return "Woof!"

Here, Dog inherits from Animal, meaning it has access to the name attribute defined in Animal.

Using the Inherited Class

dog1 = Dog("Buddy")
print(dog1.name)  # Output: Buddy
print(dog1.bark())  # Output: Woof!

3. Polymorphism

Polymorphism allows different classes to be treated as instances of the same class through shared methods, promoting flexibility in code.

Example of Polymorphism

class Cat:
    def speak(self):
        return "Meow!"

class Dog:
    def speak(self):
        return "Woof!"

def make_animal_speak(animal):
    print(animal.speak())

Both Cat and Dog have a speak() method, allowing make_animal_speak() to call speak() on any object passed to it:

dog = Dog()
cat = Cat()
make_animal_speak(dog)  # Output: Woof!
make_animal_speak(cat)  # Output: Meow!

4. Encapsulation

Encapsulation restricts access to specific parts of an object, using private methods and variables to protect the internal state.

Example of Encapsulation

class BankAccount:
    def __init__(self, balance=0):
        self.__balance = balance

    def deposit(self, amount):
        if amount > 0:
            self.__balance += amount

    def get_balance(self):
        return self.__balance

Here, __balance is a private variable, only accessible within the class through the get_balance() method.