code: def add_regional_client(self, region_name):
          
          if region_name not in self._regional_clients:
              session = boto3.session.Session(region_name=region_name, botocore_session=self.config.botocore_session)
              client = session.client("kms", config=self._user_agent_adding_config)
              self._register_client(client, region_name)
              self._regional_clients[region_name] = client
docs: Adds a regional client for the specified region if it does not already exist.
  
          :param str region_name: AWS Region ID (ex: us-east-1)