[FIXED] Multi-color Legend Entry

Issue

I would like to make a legend entry in a matplotlib look something like this:

It has multiple colors for a given legend item. Code is shown below which outputs a red rectangle. I'm wondering what I need to do to overlay one color ontop of another? Or is there a better solution?

import matplotlib.patches as mpatches
import matplotlib.pyplot as plt

red_patch = mpatches.Patch(color='red', label='Foo')
plt.legend(handles=[red_patch])

plt.show()

Solution

There is in fact a proper way to do this by implementing a custom legend handler as explained in the matplotlib-doc under "implementing a custom legend handler" (here):

import matplotlib.pyplot as plt
from matplotlib.collections import PatchCollection

# define an object that will be used by the legend
class MulticolorPatch(object):
    def __init__(self, colors):
        self.colors = colors
        
# define a handler for the MulticolorPatch object
class MulticolorPatchHandler(object):
    def legend_artist(self, legend, orig_handle, fontsize, handlebox):
        width, height = handlebox.width, handlebox.height
        patches = []
        for i, c in enumerate(orig_handle.colors):
            patches.append(plt.Rectangle([width/len(orig_handle.colors) * i - handlebox.xdescent, 
                                          -handlebox.ydescent],
                           width / len(orig_handle.colors),
                           height, 
                           facecolor=c, 
                           edgecolor='none'))

        patch = PatchCollection(patches,match_original=True)

        handlebox.add_artist(patch)
        return patch


# ------ choose some colors
colors1 = ['g', 'b', 'c', 'm', 'y']
colors2 = ['k', 'r', 'k', 'r', 'k', 'r']

# ------ create a dummy-plot (just to show that it works)
f, ax = plt.subplots()
ax.plot([1,2,3,4,5], [1,4.5,2,5.5,3], c='g', lw=0.5, ls='--',
        label='... just a line')
ax.scatter(range(len(colors1)), range(len(colors1)), c=colors1)
ax.scatter([range(len(colors2))], [.5]*len(colors2), c=colors2, s=50)

# ------ get the legend-entries that are already attached to the axis
h, l = ax.get_legend_handles_labels()

# ------ append the multicolor legend patches
h.append(MulticolorPatch(colors1))
l.append("a nice multicolor legend patch")

h.append(MulticolorPatch(colors2))
l.append("and another one")

# ------ create the legend
f.legend(h, l, loc='upper left', 
         handler_map={MulticolorPatch: MulticolorPatchHandler()}, 
         bbox_to_anchor=(.125,.875))

Answered By - raphael