def _try_next(self, get_more_allowed):
        """Advance the cursor blocking for at most one getMore command."""
        if not len(self.__data) and not self.__killed and get_more_allowed:
            self._refresh()
        if len(self.__data):
            coll = self.__collection
            return coll.database._fix_outgoing(self.__data.popleft(), coll)
        else:
            return None
Advance the cursor blocking for at most one getMore command.
stackoverflow/venv/lib/python3.6/site-packages/pymongo/command_cursor.py