def __repr__(self):
        return "<Requirement(package={package}, version='{version}')>".format(
            package=self.package, version=self.version)
def winding_current(pos, current, ax=0):
    """plot winding currents"""
    if ax == 0:
        ax = plt.gca()
    ax.set_title('Winding Currents / A')
    ax.grid(True)
    for p, i in zip(pos, current):
        ax.plot(p, i)