Building real-world projects using OOP principles

Imagine you have a big box of LEGO bricks. Each brick is a small part, but when you put it together, you can build something amazing like a castle or a spaceship. In programming, we use something called Object-Oriented Programming (OOP) to build big projects by combining small, manageable parts. Let’s learn how to do this using Python!

Real-World Project: A Simple Library System

Let’s build a small library system where you can add books, lend them to people, and return them.

Step 1: Define the Classes

We’ll need three main classes: Library, Book, and Member.

1. Library: Manages the collection of books and the members.
2. Book: Represents a book with a title and author.
3. Member: Represents a library member who can borrow books.

Code Example

Class Definitions

class Book:
    def __init__(self, title, author):
        self.title = title
        self.author = author
        self.is_borrowed = False

class Member:
    def __init__(self, name):
        self.name = name
        self.borrowed_books = []

class Library:
    def __init__(self):
        self.books = []
        self.members = []

    def add_book(self, book):
        self.books.append(book)

    def add_member(self, member):
        self.members.append(member)

    def lend_book(self, book_title, member_name):
        for book in self.books:
            if book.title == book_title and not book.is_borrowed:
                for member in self.members:
                    if member.name == member_name:
                        book.is_borrowed = True
                        member.borrowed_books.append(book)
                        return f"Book '{book_title}' has been lent to {member_name}"
        return f"Book '{book_title}' is not available"

    def return_book(self, book_title, member_name):
        for member in self.members:
            if member.name == member_name:
                for book in member.borrowed_books:
                    if book.title == book_title:
                        book.is_borrowed = False
                        member.borrowed_books.remove(book)
                        return f"Book '{book_title}' has been returned by {member_name}"
        return f"Book '{book_title}' was not borrowed by {member_name}"

Step 2: Create Objects and Use Them

Now, let’s create some books, members, and a library. We’ll add books and members to the library and perform lending and return actions.

# Create some books
book1 = Book("Harry Potter and the Philosopher's Stone", "J.K. Rowling")
book2 = Book("The Hobbit", "J.R.R. Tolkien")

# Create some members
member1 = Member("Alice")
member2 = Member("Bob")

# Create a library
library = Library()

# Add books to the library
library.add_book(book1)
library.add_book(book2)

# Add members to the library
library.add_member(member1)
library.add_member(member2)

# Lend a book to a member
print(library.lend_book("Harry Potter and the Philosopher's Stone", "Alice"))

# Return a book from a member
print(library.return_book("Harry Potter and the Philosopher's Stone", "Alice"))

Practice Questions

1. Add More Books: Create two more books and add them to the library. Write the code to do this.
2. More Members: Create one more member and add them to the library. Write the code to do this.
3. Lend and Return: Lend a book to the new member and then return it. Write the code to do this.

Practice Solutions

1. Add More Books:

# Create more books
book3 = Book("1984", "George Orwell")
book4 = Book("To Kill a Mockingbird", "Harper Lee")

# Add books to the library
library.add_book(book3)
library.add_book(book4)

2. More Members:

# Create another member
member3 = Member("Charlie")

# Add the member to the library
library.add_member(member3)

3. Lend and Return:

# Lend a book to the new member
print(library.lend_book("1984", "Charlie"))

# Return the book from the new member
print(library.return_book("1984", "Charlie"))

By using classes and objects, we can create complex systems in a simple and organized way. In this example, we built a small library system that can manage books and members, and handle lending and returning books. This is just a start! With OOP, you can build even more complex and interesting projects. Keep practicing, and you’ll become a great programmer!