library.py

import json

# ---------------- Variables & Basic Syntax ----------------
library_name = "City Central Library"
total_books = 0

# ---------------- Nested Dictionary ----------------
library = {
    "Fiction": {
        "Harry Potter": {"author": "J.K. Rowling", "copies": 3},
        "The Hobbit": {"author": "J.R.R. Tolkien", "copies": 2}
    },
    "Science": {
        "A Brief History of Time": {"author": "Stephen Hawking", "copies": 4},
        "The Selfish Gene": {"author": "Richard Dawkins", "copies": 1}
    }
}

# ---------------- Functions ----------------
def display_books():
    print(f"\n📚 {library_name} - Book List")
    for category, books in library.items():
        print(f"\nCategory: {category}")
        for title, info in books.items():
            print(f"  {title} by {info['author']} - {info['copies']} copies")

def add_book(category, title, author, copies):
    if category not in library:
        library[category] = {}
    library[category][title] = {"author": author, "copies": copies}
    print(f"✅ '{title}' added under {category}.")

def borrow_book(title):
    for category, books in library.items():
        if title in books:
            if books[title]["copies"] > 0:
                books[title]["copies"] -= 1
                print(f"📖 You borrowed '{title}'. Copies left: {books[title]['copies']}")
                return
            else:
                print("❌ No copies left!")
                return
    print("❌ Book not found.")

# ---------------- JSON Save & Load ----------------
def save_data():
    with open("library_data.json", "w") as f:
        json.dump(library, f)
    print("💾 Data saved.")

def load_data():
    global library
    try:
        with open("library_data.json", "r") as f:
            library = json.load(f)
        print("📂 Data loaded.")
    except FileNotFoundError:
        print("⚠ No saved data found.")

# ---------------- Aggregation ----------------
def total_books_count():
    total = sum(info["copies"] for books in library.values() for info in books.values())
    print(f"📊 Total books in library: {total}")

# ---------------- Program Flow ----------------
load_data()

while True:
    print("\n--- Library Menu ---")
    print("1. Display Books")
    print("2. Add Book")
    print("3. Borrow Book")
    print("4. Total Books Count")
    print("5. Save & Exit")

    choice = input("Enter choice: ")

    if choice == "1":
        display_books()
    elif choice == "2":
        cat = input("Enter category: ")
        title = input("Enter title: ")
        author = input("Enter author: ")
        copies = int(input("Enter number of copies: "))
        add_book(cat, title, author, copies)
    elif choice == "3":
        title = input("Enter title to borrow: ")
        borrow_book(title)
    elif choice == "4":
        total_books_count()
    elif choice == "5":
        save_data()
        break
    else:
        print("❌ Invalid choice. Try again.")