How To Draw 2 Planes Intersecting

          from mpl_toolkits.mplot3d import axes3d import matplotlib.pyplot as plt import numpy as np   fig = plt.figure() ax = fig.add_subplot(111, projection='3d')  dim = 10  X, Y = np.meshgrid([-dim, dim], [-dim, dim]) Z = np.zeros((2, 2))  angle = .5 X2, Y2 = np.meshgrid([-dim, dim], [0, dim]) Z2 = Y2 * angle X3, Y3 = np.meshgrid([-dim, dim], [-dim, 0]) Z3 = Y3 * angle  r = 7 M = 1000 th = np.linspace(0, 2 * np.pi, M)  x, y, z = r * np.cos(th),  r * np.sin(th), angle * r * np.sin(th)  ax.plot_surface(X2, Y3, Z3, color='blue', alpha=.5, linewidth=0, zorder=-1)  ax.plot(x[y < 0], y[y < 0], z[y < 0], lw=5, linestyle='--', color='green',         zorder=0)  ax.plot_surface(X, Y, Z, color='red', alpha=.5, linewidth=0, zorder=1)  ax.plot(r * np.sin(th), r * np.cos(th), np.zeros(M), lw=5, linestyle='--',         color='k', zorder=2)  ax.plot_surface(X2, Y2, Z2, color='blue', alpha=.5, linewidth=0, zorder=3)  ax.plot(x[y > 0], y[y > 0], z[y > 0], lw=5, linestyle='--', color='green',         zorder=4)  plt.axis('off') plt.show()

result

caveats:

I am running a version very close to the current master, so I am not sure what will work in older versions
The reason for splitting up the plotting is that 'above' and 'below' are determined in a some what arcane way (I am not strictly sure the zorder actually does anything), and is really dependent on the order the artists are drawn in. Thus surfaces can not intersect (one will be above the other every where), so you need to plot the sections on either side of the intersection separately. (You can see this in the black line which I didn't split at looks like it in 'on top of' the upper blue plane).
The 'proper' ordering of the surfaces also seems to be dependent on the view angle.