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 winding_factors(wdg, n=8, ax=0):
    """plot winding factors"""
    ax = plt.gca()
    ax.set_title(f'Winding factors Q={wdg.Q}, p={wdg.p}, q={round(wdg.q,4)}')
    ax.grid(True)
    order, kwp, kwd, kw = np.array([(n, k1, k2, k3)
                                    for n, k1, k2, k3 in zip(wdg.kw_order(n),
                                                             wdg.kwp(n),
                                                             wdg.kwd(n),
                                                             wdg.kw(n))]).T
    try:
        markerline1, stemlines1, _ = ax.stem(order-1, kwp, 'C1:', basefmt=" ",
                                             markerfmt='C1.',
                                             use_line_collection=True, label='Pitch')
        markerline2, stemlines2, _ = ax.stem(order+1, kwd, 'C2:', basefmt=" ",
                                             markerfmt='C2.',
                                             use_line_collection=True, label='Distribution')
        markerline3, stemlines3, _ = ax.stem(order, kw, 'C0-', basefmt=" ",
                                             markerfmt='C0o',
                                             use_line_collection=True, label='Total')
        ax.set_xticks(order)
        ax.legend()
    except ValueError:  # empty sequence
        pass