c1 = plt.contour(X, Y, abs(np.angle(Z) * 180 / np.pi), levels=levels)
c2 = plt.contour(X, Y, abs(np.angle(Z * np.exp(0.5j * np.pi)) * 180 / np.pi
    ), levels=levels)
Stop pyplot.contour from drawing a contour along a discontinuity