def format_results(self, results, jsonfile_prefix=None):
        """Format the results to json (standard format for COCO evaluation).

        Args:
            results (list[dict]): Testing results of the dataset.
            jsonfile_prefix (str | None): The prefix of json files. It includes
                the file path and the prefix of filename, e.g., "a/b/prefix".
                If not specified, a temp file will be created. Default: None.

        Returns:
            tuple: Returns (result_files, tmp_dir), where `result_files` is a \
                dict containing the json filepaths, `tmp_dir` is the temporal \
                directory created for saving json files when \
                `jsonfile_prefix` is not specified.
        """
        if isinstance(results, dict):
            # print(f'results must be a list, but get dict, keys={results.keys()}')
            # assert isinstance(results, list)
            results = results['bbox_results']
        assert isinstance(results, list)
        assert len(results) == len(self), (
            'The length of results is not equal to the dataset len: {} != {}'.
            format(len(results), len(self)))

        if jsonfile_prefix is None:
            tmp_dir = tempfile.TemporaryDirectory()
            jsonfile_prefix = osp.join(tmp_dir.name, 'results')
        else:
            tmp_dir = None

        # currently the output prediction results could be in two formats
        # 1. list of dict('boxes_3d': ..., 'scores_3d': ..., 'labels_3d': ...)
        # 2. list of dict('pts_bbox' or 'img_bbox':
        #     dict('boxes_3d': ..., 'scores_3d': ..., 'labels_3d': ...))
        # this is a workaround to enable evaluation of both formats on nuScenes
        # refer to https://github.com/open-mmlab/mmdetection3d/issues/449
        if not ('pts_bbox' in results[0] or 'img_bbox' in results[0]):
            result_files = self._format_bbox(results, jsonfile_prefix)
        else:
            # should take the inner dict out of 'pts_bbox' or 'img_bbox' dict
            result_files = dict()
            for name in results[0]:
                if name == 'metric_results':
                    continue
                print(f'\nFormating bboxes of {name}')
                results_ = [out[name] for out in results]
                tmp_file_ = osp.join(jsonfile_prefix, name)
                result_files.update(
                    {name: self._format_bbox(results_, tmp_file_)})
        return result_files, tmp_dir
Format the results to json (standard format for COCO evaluation).

        Args:
            results (list[dict]): Testing results of the dataset.
            jsonfile_prefix (str | None): The prefix of json files. It includes
                the file path and the prefix of filename, e.g., "a/b/prefix".
                If not specified, a temp file will be created. Default: None.

        Returns:
            tuple: Returns (result_files, tmp_dir), where `result_files` is a                 dict containing the json filepaths, `tmp_dir` is the temporal                 directory created for saving json files when                 `jsonfile_prefix` is not specified.
        
projects/mmdet3d_plugin/datasets/nuscenes_vad_dataset.py