def gt_roidb(self):
    """
    Return the database of ground-truth regions of interest.

    This function loads/saves from/to a cache file to speed up future calls.
    """
    cache_file = os.path.join(self.cache_path, self.name + '_gt_roidb.pkl')
    if os.path.exists(cache_file):
      with open(cache_file, 'rb') as fid:
        try:
          roidb = pickle.load(fid)
        except:
          roidb = pickle.load(fid, encoding='bytes')
      print('{} gt roidb loaded from {}'.format(self.name, cache_file))
      return roidb

    gt_roidb = [self._load_pascal_annotation(index)
                for index in self.image_index]
    with open(cache_file, 'wb') as fid:
      pickle.dump(gt_roidb, fid, pickle.HIGHEST_PROTOCOL)
    print('wrote gt roidb to {}'.format(cache_file))

    return gt_roidb

    Return the database of ground-truth regions of interest.

    This function loads/saves from/to a cache file to speed up future calls.
    
lib/datasets/pascal_voc_rbg.py