[FIXED] Set boxplot 'boxes' facecolor transparency

Issue

I'm looking for a way to set transparency for the boxplot facecolor. Now it appears 'red' with alpha=1. How do I change it to 'red' with alpha of 0.5 for example while keeping the boxes edge-color non-transparent 'black'? I only want transparency for the facecolor, not for the edgecolor. Any ideas?

Tried code:

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
import matplotlib.colors as cls
import matplotlib

matplotlib.interactive(True)

df = pd.DataFrame({"A": [18,28,29,32,35,36,37,37,39,40,42,42,46,48,54,56,57,61,61,62,63,65],
                   "B":  [9,13,17,15,23,21,24,28,26,30,29,30,38,42,40,48,40,51,54,50,51,57],
                   "C": [1,98,65,47,58,95,24,5,63,7,41,5,6,84,56,96,33,25,61,94,68,83]})

columns = ['A', 'B']
df_data = df.loc[:, columns]

def boxplot(y_lims, y_lime):
    plt.figure(figsize=((12.0 / 2.54), (7.42 / 2.54)), facecolor=None, edgecolor='black')  
    fig, ax = plt.subplots() 
    boxprops = dict(linestyle='-', linewidth=0.6)  
    bp = df_data.boxplot(ax=ax, grid=False, showfliers=False, boxprops=boxprops, showmeans=True, return_type='dict', patch_artist=True)
    [patch.set(facecolor='red', alpha=1.0) for patch in bp['boxes']]   #if alpha=0.5; both face and edge color are transparent, I only want the facecolor to be transparent 
    [patch.set_edgecolor('black') for patch in bp['boxes']]
    [item.set_color('black') for item in bp['whiskers']]
    [item.set_color('black') for item in bp['caps']]
    [item.set_marker('.') for item in bp['means']]
    [item.set_markerfacecolor('black') for item in bp['means']]
    [item.set_markeredgecolor('black') for item in bp['means']]
    [item.set_color('black') for item in bp['medians']]

    ax.set_ylim(y_lims, y_lime)    
    plt.show()


if __name__ == '__main__':

    Boxplot_a = boxplot(None, None)

Note: - rgba-colors didn't do the trick, the alpha is not recognised for some reason

Solution

Once alpha is set for the whole path patch, possible alpha values in RGBA edge and face colors are ignored. Pandas sets alpha to 1 internally.

So in order to make it work you need to re-set alpha to None and then specify the alpha channel in the colors as needed (e.g. 0.5 for face and 1 for edge colors):

[patch.set(alpha=None, facecolor=(1,0,0,.5)) for patch in bp['boxes']]

Edit: this is already fixed and will be available in version 1.1.0 (third item here). Then you can simply do

boxprops = dict(linestyle='-', linewidth=0.6, facecolor=(1,0,0,.5), edgecolor='k')

(no need to change the patches afterwards)

Answered By - Stef