code: def clear_dns_cache(self,
                          host: Optional[str]=None,
                          port: Optional[int]=None) -> None:
          
          if host is not None and port is not None:
              self._cached_hosts.remove((host, port))
          elif host is not None or port is not None:
              raise ValueError("either both host and port "
                               "or none of them are allowed")
          else:
              self._cached_hosts.clear()
docs: Remove specified host/port or clear all dns local cache.