Plotting a line over several graphs

Question

I don\'t know how this thing is called, or even how to describe it, so the title may be a little bit misleading.

The first attached graph was created with pyplot.

Answer 1

Relevant documentation:
http://matplotlib.sourceforge.net/api/pyplot_api.html#matplotlib.pyplot.axvline

Edit: since @DSM's answer was so much better than mine I have shamefully incorporated some of that answer in an attempt to make my answer less poor.

I've tried to handle the somewhat-general case of multiple subplots in a column (i.e. not the even-more-general case of multiple subplots, e.g. in a grid).

Thanks, @DSM, for your answer and @Artium for the question.

import matplotlib.pyplot as plt
import numpy as np

def main():
    fig = plt.figure() 

    x = np.arange(20)
    y1 = np.cos(x)
    y2 = (x**2)
    y3 = (x**3)
    yn = (y1,y2,y3)
    cut = (x > 0) & (x % 2 == 0)
    COLORS = ('b','g','k')

    for i,y in enumerate(yn):
        ax = fig.add_subplot(len(yn),1,i+1)

        ax.plot(x, y,ls='solid', color=COLORS[i], zorder=1) 
        ax.scatter(x[cut], y[cut], c='r', zorder=2)

        if i != len(yn) - 1:
            ax.set_xticklabels( () )

        for j in x[cut]:
            if i != len(yn) - 1:
                ax.axvline(x=j, ymin=-1.2, ymax=1,
                           c='r', lw=2, zorder=0, clip_on=False)
            else:
                ax.axvline(x=j, ymin=0, ymax=1,
                           c='r', lw=2, zorder=0, clip_on=False)

    fig.suptitle('Matplotlib Vertical Line Example')
    plt.show()

if __name__ == '__main__':
    main()