def train(self):
        """
        Run training.
        Returns:
            OrderedDict of results, if evaluation is enabled. Otherwise None.
        """
        super().train(self.start_epoch, self.max_epoch, self.iters_per_epoch)
        if comm.is_main_process():
            assert hasattr(
                self, "_last_eval_results"
            ), "No evaluation results obtained during training!"
            return self._last_eval_results

        Run training.
        Returns:
            OrderedDict of results, if evaluation is enabled. Otherwise None.
        
fastreid/engine/defaults.py