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 = osp.join(self.cache_path, self.name + '_gt_roidb.pkl')
        if osp.exists(cache_file):
            with open(cache_file, 'rb') as fid:
                roidb = cPickle.load(fid)
            print '{} gt roidb loaded from {}'.format(self.name, cache_file)
            return roidb

        gt_roidb = [self._load_coco_annotation(index)
                    for index in self._image_index]

        with open(cache_file, 'wb') as fid:
            cPickle.dump(gt_roidb, fid, cPickle.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/coco.py