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 _explicitfiles(kindpats):
    """Returns the potential explicit filenames from the patterns.

    >>> _explicitfiles([(b'path', b'foo/bar', b'')])
    ['foo/bar']
    >>> _explicitfiles([(b'rootfilesin', b'foo/bar', b'')])
    []
    """
    # Keep only the pattern kinds where one can specify filenames (vs only
    # directory names).
    filable = [kp for kp in kindpats if kp[0] not in ("rootfilesin",)]
    return _roots(filable)