code: def _query(self, host_object):
          
          host_to_query = host_object.relative_domain
          query_name = host_to_query.derelativize(self._query_suffix)
          try:
              return query(query_name)
          except NXDOMAIN:
              return None
docs: Query the DNSBL service for given value.
  
          :param host_object: an object representing host, created by
          self._host_factory
          :returns: an instance of dns.resolver.Answer for given value if
          it is listed. Otherwise, it returns None.