title: How do I set label for an already plotted line in matplotlib?
body: <p>In my code I've already executed</p>
  
  <pre><code>ax.plot(x, y, 'b.-', ...)
  </code></pre>
  
  <p>and need to be able to set the label for the corresponding line after the fact, to have the same effect as if I'd</p>
  
  <pre><code>ax.plot(x, y, 'b.-', label='lbl', ...)
  </code></pre>
  
  <p>Is there a way to do this in Matplotlib?</p>