def get_dir_from_zipfile(zip_file, fallback=None):
    """Return the name of the root folder in a zip file.

    :param zip_file: a :class:`zipfile.ZipFile` instance.
    :param fallback: if `None`, the name of the zip file is used. This is
        returned if the zip file contains more than one top-level directory,
        or none at all.
    """
    fallback = fallback or zip_file.filename
    directories = [name for name in zip_file.namelist() if name.endswith("/")
                   and len(PurePath(name).parts) == 1]
    return fallback if len(directories) > 1 else directories[0]
def _GetOutputStream(output_format, output_dir):
  assert output_format in _OUTPUT_FORMAT_CHOICES, 'Must specify a valid format.'
  assert output_format not in ('gtest', 'none'), (
      'Cannot set stream for \'gtest\' or \'none\' output formats.')

  if output_format == 'buildbot':
    return sys.stdout

  assert output_format in _OUTPUT_FILENAME_LOOKUP, (
      'No known filename for the \'%s\' output format' % output_format)
  output_file = os.path.join(output_dir, _OUTPUT_FILENAME_LOOKUP[output_format])
  open(output_file, 'a').close()  # Create file if it doesn't exist.
  return open(output_file, 'r+')