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 mesh(isa, with_axis=False, ax=0):
    """plot mesh of I7/ISA7 model
    Args:
      isa: Isa7 object
    """
    from matplotlib.lines import Line2D
    if ax == 0:
        ax = plt.gca()
    ax.set_aspect('equal')
    for el in isa.elements:
        pts = [list(i) for i in zip(*[v.xy for v in el.vertices])]
        ax.add_line(Line2D(pts[0], pts[1], color='b', ls='-', lw=0.25))

    # for nc in isa.nodechains:
    #    pts = [list(i) for i in zip(*[(n.x, n.y) for n in nc.nodes])]
    #    ax.add_line(Line2D(pts[0], pts[1], color="b", ls="-", lw=0.25,
    #                       marker=".", ms="2", mec="None"))

    # for nc in isa.nodechains:
    #    if nc.nodemid is not None:
    #        plt.plot(*nc.nodemid.xy, "rx")

    ax.autoscale(enable=True)
    if not with_axis:
        ax.axis('off')