OOP Lab Exercise in Python: Build a Library Management System

Master Python Object-Oriented Programming with this hands-on lab exercise. Build a Library Management System to learn encapsulation, inheritance, and polymorphism through practical coding examples.

This lab practical is designed to reinforce the three pillars of Object-Oriented Programming (OOP) by building a Library Management System.

Phase 1: Encapsulation

Encapsulation involves bundling data (attributes) and methods into a single unit and restricting direct access to some components using “private” members (indicated by a double underscore __).

1. Define the class: Create a Book class.
2. Private Attributes: Use __title and __author so they cannot be changed directly from outside the class.
3. Getter/Setter: Provide methods to access or modify these values securely.

class Book:
    def __init__(self, title, author):
        self.__title = title  # Private attribute
        self.__author = author

    def get_details(self):
        return f"'{self.__title}' by {self.__author}"

    # Getter for title
    def get_title(self):
        return self.__title

Phase 2: Inheritance

Inheritance allows a class (child) to derive attributes and methods from another class (parent).

1. Create a Subclass: Create a DigitalBook class that inherits from Book.
2. Super Function: Use super().__init__() to initialize attributes from the parent class.
3. Unique Attributes: Add a specific attribute like file_size.

class DigitalBook(Book):
    def __init__(self, title, author, file_size):
        super().__init__(title, author)
        self.file_size = file_size

    def get_details(self):
        # Extending the parent method
        return f"{super().get_details()} [Size: {self.file_size}MB]"

Phase 3: Polymorphism

Polymorphism allows different classes to be treated as instances of the same general class through the same interface (method name), even if their underlying logic differs.

1. Add another subclass: Create a PaperBook class.
2. Consistent Method Names: Ensure both subclasses use the get_details() method name.
3. Demonstrate: Use a loop to call the same method on different types of objects.

class PaperBook(Book):
    def __init__(self, title, author, weight):
        super().__init__(title, author)
        self.weight = weight

    def get_details(self):
        return f"{super().get_details()} [Weight: {self.weight}g]"

# Polymorphism in action
library = [
    DigitalBook("Python Crash Course", "Eric Matthes", 5),
    PaperBook("Automate the Boring Stuff", "Al Sweigart", 500)
]

for book in library:
    print(book.get_details())

Summary Table: How they connect

Step-by-Step Exercise Task

1. Modify the Book class to include a private attribute __is_checked_out (boolean).
2. Create a method toggle_checkout() that flips this boolean.
3. Override the get_details() method in a new subclass called ReferenceBook which always returns “Cannot be checked out” regardless of the status.