def create_book(title, author, pages, publish_date, publisher):
book = Book()
book.title = title
book.author.append(author)
book.pages = pages
if publish_date:
book.publish_date = publish_date
book.publisher = publisher
book.save()
return book
def book_add_subscriber(bk, subscriber, start, end):
book = Book(bk)
borrow = Borrow(subscriber=subscriber, start=start, end=end)
book.borrowing_history.append(borrow)
book.save()
return book