def METHOD_NAME(self, idx_spec, loader_cont_fn, **kwargs):
    if len(self) == 0:
        raise ValueError("Please call open_file() first!")
    idx_lst = self.get_matching_indexes(idx_spec)
    for idx in idx_lst:
        try:
            dst_obj = self.load_idx(idx, **kwargs)
            # call continuation function
            loader_cont_fn(dst_obj)
        except Exception as e:
            self.logger.error("Error loading index '%s': %s" % (idx, str(e)))