MODULE 7: Object-Oriented Programming (OOP)

This is Module 7, where we transition from functional programming to Object-Oriented Programming (OOP). OOP is a paradigm based on the concept of “objects,” which can contain data (attributes) and code (methods). It is essential for building large-scale, maintainable software

1. Classes & Objects

A Class is a blueprint or a template for creating objects. An Object is an instance of a class.

Example:

• Class: Car (The blueprint)
• Object: my_tesla, your_bmw (The actual physical cars)

Python

class Car:
    pass

my_tesla = Car() # Creating an object

2. Constructors (__init__)

The __init__ method is a special method called automatically when an object is created. It is used to initialize the object’s attributes.

Example:

Python

class Robot:
    def __init__(self, name):
        self.name = name # Attribute

r1 = Robot("R2-D2")

3. Instance vs. Class Variables

• Instance Variables: Unique to each object (defined inside __init__).
• Class Variables: Shared by all objects of the class (defined outside __init__).

Example:

Python

class Dog:
    species = "Canine" # Class variable (all dogs are canines)

    def __init__(self, name):
        self.name = name # Instance variable (unique name)

4. Methods

Methods are functions defined inside a class that describe the behaviors of the object. They always take self as the first argument, which refers to the specific instance of the object.

Python

class Bird:
    def fly(self):
        print("Wings flapping!")

5. The Four Pillars of OOP

A. Encapsulation

Encapsulation hides the internal state of an object and requires all interaction to be performed through public methods. In Python, we use a double underscore __ to suggest a “private” variable.

Python

class BankAccount:
    def __init__(self):
        self.__balance = 0 # Private attribute

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

B. Inheritance

Inheritance allows a class (Child) to acquire the properties and methods of another class (Parent). This promotes code reusability.

Python

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

class Dog(Animal): # Dog inherits from Animal
    def speak(self):
        print("Bark!")

C. Polymorphism

Polymorphism (meaning “many forms”) allows different classes to be treated as instances of the same general class through the same interface. Usually, this means different classes having the same method name but different logic.

Python

animals = [Dog(), Cat()]
for animal in animals:
    animal.make_sound() # Same method name, different output based on object type

D. Abstraction

Abstraction hides complex implementation details and only shows the necessary features of an object. In Python, we use the abc (Abstract Base Classes) module to enforce this.

6. Method Overriding

Method Overriding occurs when a child class provides a specific implementation of a method that is already defined in its parent class.

Example:

Python

class Parent:
    def show(self):
        print("Inside Parent")

class Child(Parent):
    def show(self): # Overriding
        print("Inside Child")

7. Real-world OOP Examples

OOP is everywhere in software development:

• Game Development: A Player class with attributes (health, level) and methods (jump, shoot).
• Banking Systems: An Account class with subclasses for SavingsAccount and CheckingAccount.
• GUI Libraries: A Button class that inherits properties from a Widget class.