using mpatches.Patch for a custom legend

I'm using the following code to create a custom matplotlib legend.

import matplotlib.patches as mpatches
import matplotlib.pyplot as plt
colors = ["g", "w"]
texts = ["Green Data Description", "RedData Description"]
patches = [ mpatches.Patch(color=colors[i], label="{:s}".format(texts[i]) ) for i in range(len(texts)) ]
plt.legend(handles=patches, bbox_to_anchor=(0.5, 0.5), loc='center', ncol=2 )

The resulted legend is as follows:

1 - The white symbol in the legend is not shown because that the default legend background is white as well. How can I set the legend background to other color ?

2 - How to change the rectangular symbols in the legend into circular shape ?

Solution 1:

Try this:

import matplotlib.pyplot as plt
import numpy as np
import matplotlib.patches as mpatches
from matplotlib.legend_handler import HandlerPatch
colors = ["g", "w"]
texts = ["Green Data Description", "RedData Description"]
class HandlerEllipse(HandlerPatch):
    def create_artists(self, legend, orig_handle,
                       xdescent, ydescent, width, height, fontsize, trans):
        center = 0.5 * width - 0.5 * xdescent, 0.5 * height - 0.5 * ydescent
        p = mpatches.Ellipse(xy=center, width=width + xdescent,
                             height=height + ydescent)
        self.update_prop(p, orig_handle, legend)
        p.set_transform(trans)
        return [p]


c = [ mpatches.Circle((0.5, 0.5), 1, facecolor=colors[i], linewidth=3) for i in range(len(texts))]
plt.legend(c,texts,bbox_to_anchor=(0.5, 0.5), loc='center', ncol=2, handler_map={mpatches.Circle: HandlerEllipse()}).get_frame().set_facecolor('#00FFCC')
plt.show()

output:

Update:

To circle, set width equals to height, in mpatches.Ellipse

Remove the outer black line, set edgecolor="none" in mpatches.Circle

code:

import matplotlib.pyplot as plt
import numpy as np
import matplotlib.patches as mpatches
from matplotlib.legend_handler import HandlerPatch
colors = ["g", "w"]
texts = ["Green Data Description", "RedData Description"]
class HandlerEllipse(HandlerPatch):
    def create_artists(self, legend, orig_handle,
                       xdescent, ydescent, width, height, fontsize, trans):
        center = 0.5 * width - 0.5 * xdescent, 0.5 * height - 0.5 * ydescent
        p = mpatches.Ellipse(xy=center, width=height + xdescent,
                             height=height + ydescent)
        self.update_prop(p, orig_handle, legend)
        p.set_transform(trans)
        return [p]


c = [ mpatches.Circle((0.5, 0.5), radius = 0.25, facecolor=colors[i], edgecolor="none" ) for i in range(len(texts))]
plt.legend(c,texts,bbox_to_anchor=(0.5, 0.5), loc='center', ncol=2, handler_map={mpatches.Circle: HandlerEllipse()}).get_frame().set_facecolor('#00FFCC')
plt.show()

New Picture:

Solution 2:

1. Setting the legend's background color can be done using the facecolor argument to plt.legend(),

    plt.legend(facecolor="plum")
   

2. To obtain a circular shaped legend handle, you may use a standard plot with a circular marker as proxy artist,

    plt.plot([],[], marker="o", ms=10, ls="")
   

Complete example:

import matplotlib.patches as mpatches
import matplotlib.pyplot as plt
colors = ["g", "w"]
texts = ["Green Data Description", "RedData Description"]
patches = [ plt.plot([],[], marker="o", ms=10, ls="", mec=None, color=colors[i], 
            label="{:s}".format(texts[i]) )[0]  for i in range(len(texts)) ]
plt.legend(handles=patches, bbox_to_anchor=(0.5, 0.5), 
           loc='center', ncol=2, facecolor="plum", numpoints=1 )

plt.show()

(Note that mec and numpoints arguments are only required for older versions of matplotlib)

For more complicated shapes in the legend, you may use a custom handler map, see the legend guide or e.g. this answer as an example