code: def get_price(self, undefined=""):
          
          return _undefined_pattern(
              "".join(self.get_subfields("020", "c")),
              lambda x: x.strip() == "",
              undefined
          )
docs: Args:
              undefined (optional): Argument, which will be returned if the
                        `price` record is not found.
  
          Returns:
              str: Price of the book (with currency) or `undefined` if `price` \
                   is not found.