code: def _prefix_description_for_number(data, longest_prefix, numobj, lang, script=None, region=None):
      
      e164_num = format_number(numobj, PhoneNumberFormat.E164)
      if not e164_num.startswith(U_PLUS):  # pragma no cover
          # Can only hit this arm if there's an internal error in the rest of
          # the library
          raise Exception("Expect E164 number to start with +")
      for prefix_len in range(longest_prefix, 0, -1):
          prefix = e164_num[1:(1 + prefix_len)]
          if prefix in data:
              # This prefix is present in the geocoding data, as a dictionary
              # mapping language info to location name.
              name = _find_lang(data[prefix], lang, script, region)
              if name is not None:
                  return name
              else:
                  return U_EMPTY_STRING
      return U_EMPTY_STRING
docs: Return a text description of a PhoneNumber for the given language.
  
      Arguments:
      data -- Prefix dictionary to lookup up number in.
      longest_prefix -- Length of the longest key in data.
      numobj -- The PhoneNumber object for which we want to get a text description.
      lang -- A 2-letter lowercase ISO 639-1 language code for the language in
                    which the description should be returned (e.g. "en")
      script -- A 4-letter titlecase (first letter uppercase, rest lowercase)
                    ISO script code as defined in ISO 15924, separated by an
                    underscore (e.g. "Hant")
      region --  A 2-letter uppercase ISO 3166-1 country code (e.g. "GB")
  
      Returns a text description in the given language code, for the given phone
      number's area, or an empty string if no description is available.