title: matplotlib - single axis label for multi-panel plot?
body: <p>I want to create a multi-panel plot:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  fig = plt.figure()
  ax1 = fig.add_subplot(2,1,1)
  ax1.scatter(1,1)
  ax2 = fig.add_subplot(2,1,2,sharex=ax1)
  ax2.scatter(1,1)
  </code></pre>
  
  <p>and then create a separate axes object just for the label...</p>
  
  <pre><code>dummy = fig.add_subplot(1,1,1)
  dummy.set_visible(False)
  dummy.yaxis.set_label_text('y label')
  dummy.yaxis.label.set_visible(True)
  </code></pre>
  
  <p>But does not work. I wonder why?</p>