class_docstr: Open Images dataset for detection.
  
  Args:
      ann_file (str): Annotation file path.
      label_file (str): File path of the label description file that
          maps the classes names in MID format to their short
          descriptions.
      meta_file (str): File path to get image metas.
      hierarchy_file (str): The file path of the class hierarchy.
      image_level_ann_file (str): Human-verified image level annotation,
          which is used in evaluation.
      backend_args (dict, optional): Arguments to instantiate the
          corresponding backend. Defaults to None.
docstr: Join ``self.data_root`` with annotation path.
docstr_tok: ["Join","``","self.data_root","``","with","annotation","path","."]
code: def _join_prefix(self):
      """Join ``self.data_root`` with annotation path."""
      super()._join_prefix()
      if not is_abs(self.label_file) and self.label_file:
          self.label_file = osp.join(self.data_root, self.label_file)
      if not is_abs(self.meta_file) and self.meta_file:
          self.meta_file = osp.join(self.data_root, self.meta_file)
      if not is_abs(self.hierarchy_file) and self.hierarchy_file:
          self.hierarchy_file = osp.join(
              self.data_root, self.hierarchy_file
          )
      if self.image_level_ann_file and not is_abs(
          self.image_level_ann_file
      ):
          self.image_level_ann_file = osp.join(
              self.data_root, self.image_level_ann_file
          )
  
imports: import csv
  import os.path
  from collections import defaultdict
  from typing import Dict, List, Optional
  import numpy
  from mmengine.fileio import get_local_path, load
  from mmengine.utils import is_abs
  from mmdet.registry import DATASETS
  from .base_det_dataset import BaseDetDataset
label_desc: Use image node_id 7 for calling the OpenImagesDataset obj's underlying member method code with example usage: obj._join_prefix() without return types