Adding a legend to a matplotlib boxplot with multiple plots on same axes

Question

I have a boxplot generated with matplotlib:

However, I have no idea how to generate the legend. Whenever I try the following I get an error saying Legend does not support {boxes: ... I've done a fair bit of searching and there doesn't seem to be an example showing how to achieve this. Any help would be appreciated!

bp1 = ax.boxplot(data1, positions=[1,4], notch=True, widths=0.35, patch_artist=True) bp2 = ax.boxplot(data2, positions=[2,5], notch=True, widths=0.35, patch_artist=True)  ax.legend([bp1, bp2], ['A', 'B'], loc='upper right') 

Answer 1

The boxplot returns a dictionary of artists

result : dict
A dictionary mapping each component of the boxplot to a list of the matplotlib.lines.Line2D instances created. That dictionary has the following keys (assuming vertical boxplots):

• boxes: the main body of the boxplot showing the quartiles and the median’s confidence intervals if enabled.
• [...]

Using the boxes, you can get the legend artists as

ax.legend([bp1["boxes"][0], bp2["boxes"][0]], ['A', 'B'], loc='upper right') 

Complete example:

import matplotlib.pyplot as plt import numpy as np; np.random.seed(1)  data1=np.random.randn(40,2) data2=np.random.randn(30,2)  fig, ax = plt.subplots() bp1 = ax.boxplot(data1, positions=[1,4], notch=True, widths=0.35,                   patch_artist=True, boxprops=dict(facecolor="C0")) bp2 = ax.boxplot(data2, positions=[2,5], notch=True, widths=0.35,                   patch_artist=True, boxprops=dict(facecolor="C2"))  ax.legend([bp1["boxes"][0], bp2["boxes"][0]], ['A', 'B'], loc='upper right')  ax.set_xlim(0,6) plt.show()