def add_to_wishlist(book_pk, username):
"""This function add a book to the wish if not duplicate."""
try:
wishlist = WishList.get((WishList.username == username)
& (WishList.book == book_pk))
except DoesNotExist:
book = BookToRent.get(BookToRent.id == book_pk)
if not book.username.username == username:
WishList.create(
book=book_pk,
username=username,
)
else:
raise SelfBook
else:
raise DuplicateEntry
