Set legend symbol opacity with matplotlib?

Question

I'm working on a plot with translucent 'x' markers (20% alpha). How do I make the marker appear at 100% opacity in the legend?

import matplotlib.pyplot as plt plt.plot_date( x = xaxis, y = yaxis, marker = 'x', color=[1, 0, 0, .2], label='Data Series' ) plt.legend(loc=3, mode="expand", numpoints=1, scatterpoints=1 ) 

Answer 1

UPDATED: There is an easier way! First, assign your legend to a variable when you create it:

leg = plt.legend() 

Then:

for lh in leg.legendHandles:      lh.set_alpha(1) 

OR if the above doesn't work (you may be using an older version of matplotlib):

for lh in leg.legendHandles:      lh._legmarker.set_alpha(1) 

to make your markers opaque for a plt.plot or a plt.scatter, respectively.

Note that using simply lh.set_alpha(1) on a plt.plot will make the lines in your legend opaque rather than the markers. You should be able to adapt these two possibilities for the other plot types.

Sources: Synthesized from some good advice by DrV about marker sizes. Update was inspired by useful comment from Owen.

Answer 2

Following up on cosmosis's answer, to make the "fake" lines for the legend invisible on the plot, you can use NaNs, and they will still work for generating legend entries:

import numpy as np import matplotlib.pyplot as plt # Plot data with alpha=0.2 plt.plot((0,1), (0,1), marker = 'x', color=[1, 0, 0, .2]) # Plot non-displayed NaN line for legend, leave alpha at default of 1.0 legend_line_1 = plt.plot( np.NaN, np.NaN, marker = 'x', color=[1, 0, 0], label='Data Series' ) plt.legend()