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 i1beta_torque(i1, beta, torque, title='', ax=0):
    """creates a surface plot of torque vs i1, beta"""
    if ax == 0:
        _create_3d_axis()
        ax = plt.gca()
    azim = 210
    if 0 < np.mean(beta) or -90 > np.mean(beta):
        azim = -60
    unit = 'Nm'
    scale = 1
    if np.min(torque) < -9.9e3 or np.max(torque) > 9.9e3:
        scale = 1e-3
        unit = 'kNm'
    if title:
        _plot_surface(ax, i1, beta, scale*np.asarray(torque),
                      (u'I1/A', u'Beta/°', title),
                      azim=azim)
    else:
        _plot_surface(ax, i1, beta, scale*np.asarray(torque),
                      (u'I1/A', u'Beta/°', u'Torque/{}'.format(unit)),
                      azim=azim)