def _run_aggregation_cmd(self, session, explicit_session):
        """Run the full aggregation pipeline for this ChangeStream and return
        the corresponding CommandCursor.
        """
        cmd = self._aggregation_command_class(
            self._target, CommandCursor, self._aggregation_pipeline(),
            self._command_options(), explicit_session,
            result_processor=self._process_result)

        return self._client._retryable_read(
            cmd.get_cursor, self._target._read_preference_for(session),
            session)
Run the full aggregation pipeline for this ChangeStream and return
        the corresponding CommandCursor.
        
stackoverflow/venv/lib/python3.6/site-packages/pymongo/change_stream.py