code: def lookup(self, host_value):
          
          try:
              host_object = self._host_factory(host_value)
          except InvalidHostError:
              return None
          result = self._get_match_and_classification(
              host_object
          )
          host_item, classification = result
          if host_item is not None:
              return AddressListItem(
                  host_item.to_unicode(),
                  self,
                  classification
              )
          return None
docs: Get a host value matching the given value.
  
          :param host_value: a value of the host of a type that can be
          listed by the service
          :returns: an instance of AddressListItem representing
          a matched value
          :raises InvalidHostError: if the argument is not a valid
          host string