📚 Project 03: Library Management System

📚 LIBRARY MANAGEMENT SYSTEM
=============================
 
1. View Catalog
2. Add Book
3. Register Member
4. Borrow Book
5. Return Book
6. View Member Info
7. Exit
 
Choose: 4
 
Enter Member ID: M001
Enter Book ISBN: 978-0-13-110362-7
 
✅ "The C Programming Language" has been borrowed by Alice.
   Due date: 2025-02-15
   Books borrowed: 1/3

cd projects/03_library_management
python solution.py

"""
================================================================================
Project 03: Library Management System
Difficulty: 🟠 Advanced
================================================================================
 
An object-oriented Library Management System for managing books, members,
and borrow/return operations with proper validation and error handling.
 
Concepts Used:
- Classes and Objects
- Inheritance and Encapsulation
- Properties and Methods
- Custom Exceptions
- __str__ and __repr__ magic methods
- Composition (Library has Books and Members)
 
================================================================================
"""
 
from datetime import datetime, timedelta
 
 
# -----------------------------------------------------------------------------
# Custom Exceptions
# -----------------------------------------------------------------------------
 
class LibraryError(Exception):
    """Base exception for library errors."""
    pass
 
 
class BookNotFoundError(LibraryError):
    """Raised when a book is not found."""
    pass
 
 
class BookNotAvailableError(LibraryError):
    """Raised when a book is already borrowed."""
    pass
 
 
class MemberNotFoundError(LibraryError):
    """Raised when a member is not found."""
    pass
 
 
class BorrowLimitError(LibraryError):
    """Raised when a member has reached their borrow limit."""
    pass
 
 
# -----------------------------------------------------------------------------
# Book Class
# -----------------------------------------------------------------------------
 
class Book:
    """Represents a book in the library."""
 
    def __init__(self, title: str, author: str, isbn: str):
        self._title = title
        self._author = author
        self._isbn = isbn
        self._is_available = True
        self._borrowed_by = None
        self._due_date = None
 
    @property
    def title(self) -> str:
        return self._title
 
    @property
    def author(self) -> str:
        return self._author
 
    @property
    def isbn(self) -> str:
        return self._isbn
 
    @property
    def is_available(self) -> bool:
        return self._is_available
 
    @property
    def due_date(self):
        return self._due_date
 
    def borrow(self, member_id: str, days: int = 14) -> None:
        """Mark the book as borrowed."""
        if not self._is_available:
            raise BookNotAvailableError(
                f'"{self._title}" is already borrowed.'
            )
        self._is_available = False
        self._borrowed_by = member_id
        self._due_date = datetime.now() + timedelta(days=days)
 
    def return_book(self) -> None:
        """Mark the book as returned."""
        self._is_available = True
        self._borrowed_by = None
        self._due_date = None
 
    def __str__(self) -> str:
        status = "✅ Available" if self._is_available else f"❌ Borrowed (due: {self._due_date.strftime('%Y-%m-%d')})"
        return f'"{self._title}" by {self._author} [ISBN: {self._isbn}] — {status}'
 
    def __repr__(self) -> str:
        return f"Book(title='{self._title}', author='{self._author}', isbn='{self._isbn}')"
 
 
# -----------------------------------------------------------------------------
# Member Class
# -----------------------------------------------------------------------------
 
class Member:
    """Represents a library member."""
 
    MAX_BORROW_LIMIT = 3
 
    def __init__(self, name: str, member_id: str):
        self._name = name
        self._member_id = member_id
        self._borrowed_books: list[str] = []  # List of ISBNs
 
    @property
    def name(self) -> str:
        return self._name
 
    @property
    def member_id(self) -> str:
        return self._member_id
 
    @property
    def borrowed_books(self) -> list:
        return self._borrowed_books.copy()
 
    @property
    def borrow_count(self) -> int:
        return len(self._borrowed_books)
 
    def can_borrow(self) -> bool:
        """Check if the member can borrow more books."""
        return self.borrow_count < self.MAX_BORROW_LIMIT
 
    def add_book(self, isbn: str) -> None:
        """Add a book ISBN to the borrowed list."""
        if not self.can_borrow():
            raise BorrowLimitError(
                f"{self._name} has reached the borrow limit ({self.MAX_BORROW_LIMIT} books)."
            )
        self._borrowed_books.append(isbn)
 
    def remove_book(self, isbn: str) -> None:
        """Remove a book ISBN from the borrowed list."""
        if isbn in self._borrowed_books:
            self._borrowed_books.remove(isbn)
 
    def __str__(self) -> str:
        return (
            f"👤 {self._name} (ID: {self._member_id}) "
            f"— Books borrowed: {self.borrow_count}/{self.MAX_BORROW_LIMIT}"
        )
 
    def __repr__(self) -> str:
        return f"Member(name='{self._name}', member_id='{self._member_id}')"
 
 
# -----------------------------------------------------------------------------
# Library Class (Composition)
# -----------------------------------------------------------------------------
 
class Library:
    """Manages books and members."""
 
    def __init__(self, name: str):
        self.name = name
        self._books: dict[str, Book] = {}       # ISBN -> Book
        self._members: dict[str, Member] = {}   # member_id -> Member
 
    # --- Book Management ---
 
    def add_book(self, title: str, author: str, isbn: str) -> Book:
        """Add a new book to the catalog."""
        if isbn in self._books:
            print(f"  ⚠️  Book with ISBN {isbn} already exists.")
            return self._books[isbn]
 
        book = Book(title, author, isbn)
        self._books[isbn] = book
        return book
 
    def find_book(self, isbn: str) -> Book:
        """Find a book by ISBN."""
        if isbn not in self._books:
            raise BookNotFoundError(f"No book found with ISBN: {isbn}")
        return self._books[isbn]
 
    def search_books(self, query: str) -> list[Book]:
        """Search books by title or author."""
        query_lower = query.lower()
        return [
            book for book in self._books.values()
            if query_lower in book.title.lower() or query_lower in book.author.lower()
        ]
 
    # --- Member Management ---
 
    def register_member(self, name: str, member_id: str) -> Member:
        """Register a new library member."""
        if member_id in self._members:
            print(f"  ⚠️  Member ID {member_id} already exists.")
            return self._members[member_id]
 
        member = Member(name, member_id)
        self._members[member_id] = member
        return member
 
    def find_member(self, member_id: str) -> Member:
        """Find a member by ID."""
        if member_id not in self._members:
            raise MemberNotFoundError(f"No member found with ID: {member_id}")
        return self._members[member_id]
 
    # --- Borrow / Return ---
 
    def borrow_book(self, member_id: str, isbn: str) -> None:
        """Allow a member to borrow a book."""
        member = self.find_member(member_id)
        book = self.find_book(isbn)
 
        if not member.can_borrow():
            raise BorrowLimitError(
                f"{member.name} has reached the borrow limit."
            )
 
        book.borrow(member_id)
        member.add_book(isbn)
        print(f'  ✅ "{book.title}" has been borrowed by {member.name}.')
        print(f"     Due date: {book.due_date.strftime('%Y-%m-%d')}")
        print(f"     Books borrowed: {member.borrow_count}/{Member.MAX_BORROW_LIMIT}")
 
    def return_book(self, member_id: str, isbn: str) -> None:
        """Allow a member to return a book."""
        member = self.find_member(member_id)
        book = self.find_book(isbn)
 
        book.return_book()
        member.remove_book(isbn)
        print(f'  ✅ "{book.title}" has been returned by {member.name}.')
 
    # --- Display ---
 
    def display_catalog(self) -> None:
        """Display the full library catalog."""
        if not self._books:
            print("  📭 No books in the catalog.")
            return
 
        print(f"\n  📚 {self.name} — Catalog ({len(self._books)} books)")
        print(f"  {'='*65}")
        for book in self._books.values():
            print(f"  {book}")
 
    def display_members(self) -> None:
        """Display all members."""
        if not self._members:
            print("  📭 No registered members.")
            return
 
        print(f"\n  👥 Registered Members ({len(self._members)})")
        print(f"  {'='*50}")
        for member in self._members.values():
            print(f"  {member}")
 
 
# -----------------------------------------------------------------------------
# Interactive Menu
# -----------------------------------------------------------------------------
 
def display_menu():
    """Display the main menu."""
    print("""
╔══════════════════════════════════════════╗
║    📚 LIBRARY MANAGEMENT SYSTEM 📚      ║
╠══════════════════════════════════════════╣
║  1. View Catalog                        ║
║  2. Add Book                            ║
║  3. Search Books                        ║
║  4. Register Member                     ║
║  5. Borrow Book                         ║
║  6. Return Book                         ║
║  7. View Member Info                    ║
║  8. Exit                                ║
╚══════════════════════════════════════════╝
    """)
 
 
def main():
    """Main entry point."""
    library = Library("City Public Library")
 
    # Pre-load some sample data
    library.add_book("The C Programming Language", "Kernighan & Ritchie", "978-0-13-110362-7")
    library.add_book("Clean Code", "Robert C. Martin", "978-0-13-235088-4")
    library.add_book("Python Crash Course", "Eric Matthes", "978-1-59327-603-4")
    library.add_book("Design Patterns", "Gang of Four", "978-0-20-163361-0")
    library.add_book("The Pragmatic Programmer", "Hunt & Thomas", "978-0-20-161622-4")
 
    library.register_member("Alice", "M001")
    library.register_member("Bob", "M002")
 
    while True:
        display_menu()
        choice = input("  Choose an option (1-8): ").strip()
 
        try:
            if choice == "1":
                library.display_catalog()
 
            elif choice == "2":
                title = input("  Enter title: ").strip()
                author = input("  Enter author: ").strip()
                isbn = input("  Enter ISBN: ").strip()
                if title and author and isbn:
                    library.add_book(title, author, isbn)
                    print(f'  ✅ "{title}" added to the catalog.')
                else:
                    print("  ❌ All fields are required.")
 
            elif choice == "3":
                query = input("  Search (title or author): ").strip()
                results = library.search_books(query)
                if results:
                    print(f"\n  🔍 Found {len(results)} result(s):")
                    for book in results:
                        print(f"  {book}")
                else:
                    print("  📭 No matching books found.")
 
            elif choice == "4":
                name = input("  Enter member name: ").strip()
                member_id = input("  Enter member ID: ").strip()
                if name and member_id:
                    library.register_member(name, member_id)
                    print(f"  ✅ {name} registered as member {member_id}.")
                else:
                    print("  ❌ All fields are required.")
 
            elif choice == "5":
                library.display_members()
                member_id = input("\n  Enter Member ID: ").strip()
                library.display_catalog()
                isbn = input("\n  Enter Book ISBN: ").strip()
                library.borrow_book(member_id, isbn)
 
            elif choice == "6":
                member_id = input("  Enter Member ID: ").strip()
                isbn = input("  Enter Book ISBN: ").strip()
                library.return_book(member_id, isbn)
 
            elif choice == "7":
                library.display_members()
                member_id = input("\n  Enter Member ID for details: ").strip()
                member = library.find_member(member_id)
                print(f"\n  {member}")
                if member.borrowed_books:
                    print("  Borrowed books:")
                    for isbn in member.borrowed_books:
                        book = library.find_book(isbn)
                        print(f"    📖 {book}")
                else:
                    print("  No books currently borrowed.")
 
            elif choice == "8":
                print("\n  👋 Thank you for using the Library Management System!")
                break
 
            else:
                print("  ❌ Invalid option. Please choose 1-8.")
 
        except LibraryError as e:
            print(f"  ❌ {e}")
 
        input("\n  Press Enter to continue...")
 
 
if __name__ == "__main__":
    main()