code: def shutdown(self, save=None):
          
          if save is self.SHUTDOWN_SAVE:
              return self.execute(b'SHUTDOWN', b'SAVE')
          elif save is self.SHUTDOWN_NOSAVE:
              return self.execute(b'SHUTDOWN', b'NOSAVE')
          else:
              return self.execute(b'SHUTDOWN')
docs: Synchronously save the dataset to disk and then
          shut down the server.