docs: def set_state(self, updater=None, **kwargs):
          """Update the datastore.
  
          :param func|dict updater: (state) => state_change or dict state_change
          :rtype: Iterable[tornado.concurrent.Future]
          """
          if callable(updater):
              state_change = updater(self)
          elif updater is not None:
              state_change = updater
          else:
              state_change = kwargs
  
          return [callback_result
                  for k, v in state_change.items()
                  for callback_result in self.set(k, v)]