title: Adding a legend to a matplotlib boxplot with multiple plots on same axes
body: <p>I have a boxplot generated with matplotlib:</p>
  
  <p><a href="https://i.stack.imgur.com/KF4Q2.png" rel="noreferrer"><img src="https://i.stack.imgur.com/KF4Q2.png" alt="enter image description here"></a></p>
  
  <p>However, I have no idea how to generate the legend. Whenever I try the following I get an error saying <code>Legend does not support {boxes: ...</code> 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!</p>
  
  <pre><code>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')
  </code></pre>