Matplotlib transparent line plots

Question

I am plotting two similar trajectories in matplotlib and I\'d like to plot each of the lines with partial transparency so that the red (plotted second) doesn\'t obscure the

Answer 1

After I plotted all the lines, I was able to set the transparency of all of them as follows:

for l in fig_field.gca().lines:
    l.set_alpha(.7)

EDIT: please see Joe's answer in the comments.