title: matplotlib 2nd axis label not showing
body: <p>With matplotlib how can I get a 2nd y-axis label to show? This is what I have tried:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  x = [0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.65]
  y = [0, 0.15, 0.3, 0.35, 0.4, 0.55, 0.57, 0.58]
  fig = plt.figure()
  ax1 = fig.add_subplot(111)
  ax2 = ax1.twinx().twiny()
  ax2.set_xlabel('2nd x-axis label')
  ax2.set_ylabel('2nd y-axis label')
  ax1.set_xlim([0,1])
  ax1.plot(x, y)
  plt.show()
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/73Yjs.png" alt="enter image description here"></p>