code: def _isbn_cleaner(fn):
      
      @wraps(fn)
      def wrapper(isbn):
          return fn(_clean_isbn(isbn))
  
      return wrapper
docs: Decorator for calling other functions from this module.
  
      Purpose of this decorator is to clean the ISBN string from garbage and
      return list of digits.
  
      Args:
          fn (function): function in which will be :func:`_clean_isbn(isbn)` call
                         wrapped.