'Tarfile with file that extracts to outside directory.
Extracting this tarfile in directory <dir> will put its contents
directly in <dir> (rather than <dir/tarname>).'

def _outside_tar(self):

    outside_tar = (self.unsafe_common_dir / 'unsafe_file.tar.gz')
    with tarfile.open(outside_tar, 'w:gz') as tar:
        tar.addfile(tarfile.TarInfo(str((self.content_dir / 'a_file'))))
    return outside_tar
