I have created a method in a model,

def update_book_price(self, book, updated_price):
    if not book:
        raise UserError('The book is not found')

    book.retail_price = updated_price

I tried calling this method from XML file like this,

    ref('library.book_the_alchemist')
    499

I have provided two arguments for the method here. but an error shows up,

TypeError: Book.update_book_price() missing 1 required positional argument: 'updated_price'

I think its because the first argument is passed to 'self'. How do i fix this?