docs: def _archive_extensions():
          """Create translations from file extension to archive format
  
          Returns
          -------
          dict
              The mapping from file extension to archive format
          dict
              The mapping from archive format to default file extension
          """
          if six.PY3:
              ext_map = {}
              fmt_map = {}
              for key, exts, desc in shutil.get_unpack_formats():
                  fmt_map[key] = exts[0]
                  for ext in exts:
                      ext_map[ext] = key
          else:
              ext_map = {'.tar': 'tar',
                         '.tar.bz2': 'bztar',
                         '.tar.gz': 'gztar',
                         '.tar.xz': 'xztar',
                         '.tbz2': 'bztar',
                         '.tgz': 'gztar',
                         '.txz': 'xztar',
                         '.zip': 'zip'}
              fmt_map = {'bztar': '.tar.bz2',
                         'gztar': '.tar.gz',
                         'tar': '.tar',
                         'xztar': '.tar.xz',
                         'zip': '.zip'}
          return ext_map, fmt_map