Chapter 9: Object-Oriented Programming (OOP)

9.1 Chapter Overview

Object-Oriented Programming, commonly known as OOP, is a programming approach that organizes code using objects. An object represents a real-world item such as a student, course, employee, vehicle, product, account, or training centre.

In this chapter, learners will understand how Python uses classes and objects to create structured, reusable, and professional programs. Learners will also study four major OOP concepts: class, object, inheritance, encapsulation, and abstraction.

9.2 Chapter Objectives

• Understand the meaning and purpose of Object-Oriented Programming.
• Explain the difference between a class and an object.
• Create Python classes using attributes and methods.
• Create objects from classes.
• Understand and apply inheritance.
• Understand encapsulation and data protection.
• Understand abstraction and simplified design.
• Develop beginner-friendly OOP applications in Python.

Learning Outcomes

• Create simple Python classes and objects.
• Use constructors with __init__().
• Define object attributes and methods.
• Apply inheritance to reuse class features.
• Use encapsulation to protect data.
• Explain abstraction in simple programming terms.

9.3 What is Object-Oriented Programming?

Object-Oriented Programming is a method of programming where software is designed using objects. Each object contains data and actions. The data is stored as attributes, and the actions are written as methods.

9.4 Why OOP is Important

OOP is widely used in professional software development because it makes programs more organized, reusable, scalable, and easier to maintain.

9.5 Classes in Python

A class is a blueprint or template used to create objects. A class defines what data an object will store and what actions the object can perform.

Basic Class Example

class Student:
    name = "Amin"
    course = "Python Programming"

print(Student.name)
print(Student.course)

9.6 Objects in Python

An object is an instance of a class. Once a class is created, we can create many objects from it.

Creating an Object

class Student:
    name = "Amin"
    course = "Python Programming"

student1 = Student()

print(student1.name)
print(student1.course)

In this example, student1 is an object created from the Student class.

9.7 Constructor using __init__()

The __init__() method is called automatically when an object is created. It is commonly used to set initial values for object attributes.

Example

class Student:
    def __init__(self, name, course):
        self.name = name
        self.course = course

student1 = Student("Amin", "Python")
student2 = Student("Mei Ling", "AI")

print(student1.name, student1.course)
print(student2.name, student2.course)

9.8 Methods in Classes

A method is a function inside a class. Methods describe the actions an object can perform.

class Student:
    def __init__(self, name, course):
        self.name = name
        self.course = course

    def display_profile(self):
        print("Student Name:", self.name)
        print("Course:", self.course)

student1 = Student("Amin", "Certified Python Programmer")
student1.display_profile()

9.9 Encapsulation

Encapsulation means keeping data and methods together inside a class. It also helps protect data from being changed directly from outside the class.

In Python, attributes can be treated as protected or private by using underscores.

Encapsulation Example

class Student:
    def __init__(self, name, marks):
        self.name = name
        self.__marks = marks

    def display_marks(self):
        print("Marks:", self.__marks)

student1 = Student("Amin", 85)
student1.display_marks()

9.10 Getter and Setter Methods

Getter and setter methods are used to access and update private data safely.

class Student:
    def __init__(self, name, marks):
        self.name = name
        self.__marks = marks

    def get_marks(self):
        return self.__marks

    def set_marks(self, marks):
        if marks >= 0 and marks <= 100:
            self.__marks = marks
        else:
            print("Invalid marks")

student1 = Student("Amin", 80)

print(student1.get_marks())

student1.set_marks(90)

print(student1.get_marks())

9.11 Inheritance

Inheritance allows one class to reuse the attributes and methods of another class. The original class is called the parent class, and the new class is called the child class.

Example

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

    def display_name(self):
        print("Name:", self.name)

class Student(Person):
    def display_role(self):
        print("Role: Student")

student1 = Student("Amin")

student1.display_name()
student1.display_role()

9.12 Types of Inheritance

9.13 Abstraction

Abstraction means showing only important details and hiding unnecessary implementation details. In simple terms, users can use a feature without knowing how it works internally.

For example, when a student clicks a login button, they do not need to know the full coding logic behind authentication. They only see the simple action: enter username and password.

Simple Abstraction Example

class Payment:
    def process_payment(self):
        print("Processing payment securely...")

payment1 = Payment()
payment1.process_payment()

9.14 Practical Example: Course Registration System

This example uses OOP to create a simple student registration system.

class Student:
    def __init__(self, name, course, fee):
        self.name = name
        self.course = course
        self.fee = fee

    def display_registration(self):
        print("----- Registration Details -----")
        print("Student Name:", self.name)
        print("Course:", self.course)
        print("Course Fee: RM", self.fee)

student1 = Student("Amin", "Certified Python Programmer", 1500)
student1.display_registration()

9.15 Practical Example: Employee and Trainer Inheritance

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

    def display_employee(self):
        print("Employee Name:", self.name)

class Trainer(Employee):
    def display_trainer_role(self):
        print("Role: Python Trainer")

trainer1 = Trainer("Dr. Kumar")

trainer1.display_employee()
trainer1.display_trainer_role()

9.16 Common Beginner Mistakes

9.17 Hands-On Practice

9.18 Final Assessment Quiz

Answer the following questions. Correct Answer = +1 Mark Wrong Answer = -0.5 Mark

Final Practical Assessment

Develop a Python program named oop_student_management.py. The program must include a Student class, constructor, attributes, display method, encapsulated marks, getter and setter methods, and a CertifiedStudent class that inherits from Student.

9.19 Chapter Summary

In this chapter, learners studied Object-Oriented Programming in Python. They learned how to create classes, objects, constructors, attributes and methods. They also explored inheritance, encapsulation and abstraction, which are important principles in professional software development.