def _download_single(self, url_or_filename: str, download_config: DownloadConfig) -> str:
        url_or_filename = str(url_or_filename)
        if is_relative_path(url_or_filename):
            # append the relative path to the base_path
            url_or_filename = url_or_path_join(self._base_path, url_or_filename)
        out = cached_path(url_or_filename, download_config=download_config)
        out = tracked_str(out)
        out.set_origin(url_or_filename)
        return out

    def iter_archive(self, path_or_buf: Union[str, io.BufferedReader]):
        """Iterate over files within an archive.

        Args:
            path_or_buf (`str` or `io.BufferedReader`):
                Archive path or archive binary file object.

        Yields:
            `tuple[str, io.BufferedReader]`:
                2-tuple (path_within_archive, file_object).
                File object is opened in binary mode.

        Example: