code: def watch(self, key, pipeline=False):
          
          if pipeline:
              self._pipeline.watch(key)
          else:
              self._db.watch(key)
docs: Watch the given key.
  
          Marks the given key to be watch for conditional execution
          of a transaction.
  
          Args:
              key (str): Key that needs to be watched
              pipeline (bool): True, start a transaction block. Default false.