def reserveBook(self,name, student_id, book_title, days): for book in Catalog.books_list: if book.title == book_title and len(book.book_item) != 0: book_item = book.book_item.pop() book.total_count -= 1 Catalog.updateIssuerInfo(book_item, name, student_id, days) Catalog.addToReservedList(book_item) return book_item else: print("The book you're trying to reserve is unavailable.")