def get_installed_pypackages():
    return {p.project_name.lower(): p for p in pkg_resources.working_set}
def voltage(title, pos, voltage, ax=0):
    """plot voltage vs. position"""
    if ax == 0:
        ax = plt.gca()
    ax.set_title('{} / V'.format(title))
    ax.grid(True)
    ax.plot(pos, voltage)