Is this solution close enough to your liking? It is slighty inspired by Ricardo's answer, but I only used one legend-object for each column, and then utilised the title
-keyword to set the title of each individual column. To put the markers in the center of each column I used handletextpad
with a negative value to push it backward. There are no legends to individual lines. I also had to insert some spaces into the title-strings to make them look equally big when drawn on screen.
I also noticed now when the figure was saved that additional tweaks to the exact position of the legend-boxes and are needed, but since I guess you might want to tweak more stuff in the code anyway I leave it for you. You might also need to play yourself with the handletextpad
to make them "perfectly" aligned.
import matplotlib.pylab as plt
import numpy as np
plt.close('all')
N = 25
y = np.random.randn(N)
x = np.arange(N)
y2 = np.random.randn(25)
# serie A
p1a, = plt.plot(x, y, "ro", ms=10, mfc="r", mew=2, mec="r")
p1b, = plt.plot(x[:5], y[:5] , "w+", ms=10, mec="w", mew=2)
p1c, = plt.plot(x[5:10], y[5:10], "w*", ms=10, mec="w", mew=2)
# serie B
p2a, = plt.plot(x, y2, "bo", ms=10, mfc="b", mew=2, mec="b")
p2b, = plt.plot(x[15:20], y2[15:20] , "w+", ms=10, mec="w", mew=2)
p2c, = plt.plot(x[10:15], y2[10:15], "w*", ms=10, mec="w", mew=2)
line_columns = [
p1a, p2a,
(p1a, p1b), (p2a, p2b),
(p1a, p1c), (p2a, p2c)
]
leg1 = plt.legend(line_columns[0:2], ['', ''], ncol=1, numpoints=1,
title='No prop', handletextpad=-0.4,
bbox_to_anchor=[0.738, 1.])
leg2 = plt.legend(line_columns[2:4], ['', ''], ncol=1, numpoints=1,
title=' Prop + ', handletextpad=-0.4,
bbox_to_anchor=[0.87, 1.])
leg3 = plt.legend(line_columns[4:6], ['', ''], ncol=1, numpoints=1,
title=' Prop * ', handletextpad=-0.4,
bbox_to_anchor=[0.99, 1.])
plt.gca().add_artist(leg1)
plt.gca().add_artist(leg2)
plt.gca().add_artist(leg3)
plt.gcf().show()
Edit
Maybe this will work better. You still have to tweak a few stuff, but the alignment-problem of the bboxes are away.
leg = plt.legend(line_columns, ['']*len(line_columns),
title='No Prop Prop + Prop *',
ncol=3, numpoints=1, handletextpad=-0.5)