Set predictor for continued training.

        It is not recommended for user to call this function.
        Please use init_model argument in engine.train() or engine.cv() instead.

def _set_predictor(self, predictor):
        """Set predictor for continued training.

        It is not recommended for user to call this function.
        Please use init_model argument in engine.train() or engine.cv() instead.
        """
        if predictor is self._predictor:
            return self
        if self.data is not None:
            self._predictor = predictor
            return self._free_handle()
        else:
            raise LightGBMError("Cannot set predictor after freed raw data, "
                                "set free_raw_data=False when construct Dataset to avoid this.")