Question

class Book:
# Class attribute to keep track of the total copies
available_copies = 0

def __init__(self, title, author, year, copies):
# Instance attributes
self.title = title
self.author = author
self.year = year

# Initialize available copies
Book.available_copies += copies
self.copies = copies

def borrow(self):
"""Method to borrow a book, decreases available copies if possible."""
global borrowed # Indicating we are using a global variable
if Book.available_copies > 0:
Book.available_copies -= 1
borrowed += 1
print(f"You have borrowed '{self.title}'. {Book.available_copies} copies left.")
else:
print(f"Sorry, '{self.title}' is currently not available.")

def return_book(self):
"""Method to return a book, increases available copies."""
global borrowed # Indicating we are using a global variable
if borrowed > 0:
Book.available_copies += 1
borrowed -= 1
print(f"You have returned '{self.title}'. {Book.available_copies} copies available now.")
else:
print("No borrowed books to return.")

def display_info(self):
"""Method to display book information."""
print(f"Title: {self.title}, Author: {self.author}, Year: {self.year}, Available Copies: {Book.available_copies}")

# Global variable to keep track of borrowed books
borrowed = 0

# Test the Book class by instantiating several objects and demonstrating methods
# Create book instances
book1 = Book("1984", "George Orwell", 1949, 5)
book2 = Book("To Kill a Mockingbird", "Harper Lee", 1960, 3)

# Display information of the books
book1.display_info()
book2.display_info()

# Borrow books
book1.borrow()
book2.borrow()

# Current state after borrowing
book1.display_info()
book2.display_info()

# Return books
book1.return_book()
book2.return_book()

# Final state
book1.display_info()
book2.display_info(

Answer 1

Your code for the `Book` class and its usage is generally good, but there are a few improvements and corrections that can be made to enhance readability and functionality. Here are some suggestions:

1. Remove the use of global variables where possible. Instead, maintain the borrowed count as an instance variable.
2. Add error handling to prevent returning more books than were borrowed.
3. The `available_copies` should be updated based on the number of books you are borrowing or returning individually, rather than a global count for all books.

Here’s the revised implementation:

```python
class Book:
# Class attribute to keep track of the total available copies
def __init__(self, title, author, year, copies):
# Instance attributes
self.title = title
self.author = author
self.year = year
self.available_copies = copies # Each book keeps track of its own available copies
self.borrowed_copies = 0 # Track how many copies are currently borrowed

def borrow(self):
"""Method to borrow a book, decreases available copies if possible."""
if self.available_copies > 0:
self.available_copies -= 1
self.borrowed_copies += 1
print(f"You have borrowed '{self.title}'. {self.available_copies} copies left.")
else:
print(f"Sorry, '{self.title}' is currently not available.")

def return_book(self):
"""Method to return a book, increases available copies."""
if self.borrowed_copies > 0:
self.available_copies += 1
self.borrowed_copies -= 1
print(f"You have returned '{self.title}'. {self.available_copies} copies available now.")
else:
print("No borrowed books to return.")

def display_info(self):
"""Method to display book information."""
print(f"Title: {self.title}, Author: {self.author}, Year: {self.year}, Available Copies: {self.available_copies}")

# Test the Book class by instantiating several objects and demonstrating methods
# Create book instances
book1 = Book("1984", "George Orwell", 1949, 5)
book2 = Book("To Kill a Mockingbird", "Harper Lee", 1960, 3)

# Display information of the books
book1.display_info()
book2.display_info()

# Borrow books
book1.borrow()
book2.borrow()

# Current state after borrowing
book1.display_info()
book2.display_info()

# Return books
book1.return_book()
book2.return_book()

# Final state
book1.display_info()
book2.display_info()
```

### Summary of Changes:

- Removed the global variable and instead used instance attributes for managing borrowed copies.
- Each book now independently manages its own count of available and borrowed copies.
- The `borrow` and `return_book` methods ensure they respect the individual book's counts.

This design is more modular and adheres better to object-oriented principles, allowing easier tracking of each book's state.