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):
            fid = gzip.open(cache_file,'rb')
            roidb = pickle.load(fid)
            fid.close()
            print('{} gt roidb loaded from {}'.format(self.name, cache_file))
            return roidb

        gt_roidb = [self._load_vg_annotation(index)
                    for index in self.image_index]
        fid = gzip.open(cache_file,'wb')
        pickle.dump(gt_roidb, fid, pickle.HIGHEST_PROTOCOL)
        fid.close()
        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/vg.py