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 _remainingpats(pat, prefix):
    """list of patterns with prefix stripped

    >>> _remainingpats("a/b/c", "")
    ['a/b/c']
    >>> _remainingpats("a/b/c", "a")
    ['b/c']
    >>> _remainingpats("a/b/c", "a/b")
    ['c']
    >>> _remainingpats("a/b/c", "a/b/c")
    []
    >>> _remainingpats("", "")
    []
    """
    if prefix:
        if prefix == pat:
            return []
        else:
            assert pat[len(prefix)] == "/"
            return [pat[len(prefix) + 1 :]]
    else:
        if pat:
            return [pat]
        else:
            return []