code: def _set_keyspace_for_all_conns(self, keyspace, callback):
          
          remaining_callbacks = set(self._connections)
          errors = []
  
          if not remaining_callbacks:
              callback(self, errors)
              return
  
          def connection_finished_setting_keyspace(conn, error):
              self.return_connection(conn)
              remaining_callbacks.remove(conn)
              if error:
                  errors.append(error)
  
              if not remaining_callbacks:
                  callback(self, errors)
  
          self._keyspace = keyspace
          for conn in self._connections:
              conn.set_keyspace_async(keyspace, connection_finished_setting_keyspace)
docs: Asynchronously sets the keyspace for all connections.  When all
          connections have been set, `callback` will be called with two
          arguments: this pool, and a list of any errors that occurred.