title: How to label y-axis when using a secondary y-axis?
body: <p>I am trying to label both y-axis, one to say "WLL", the other to say "S&amp;P 500". Right now, I can only label the secondary y-axis (S&amp;P 500).  </p>
  
  <pre><code>import pandas as pd
  from pandas import DataFrame
  from matplotlib import pyplot as plt
  import pandas.io.data as web
  import datetime as dt
  
  start = '2013-01-01'
  end = dt.datetime.today()
  
  df = web.DataReader('WLL', 'yahoo', start, end)
  sp = web.DataReader('^GSPC', 'yahoo', start, end)
  
  fig, ax1 = plt.subplots()
  df['Close'].plot(ax=ax1,color='g',linewidth=1.0)
  sp['Close'].plot(secondary_y=True, ax=ax1,color='b',linewidth=1.0)
  ax = df['Close'].plot(); sp['Close'].plot(ax=ax, secondary_y=True)
  
  plt.xlabel('xlabel', fontsize=10)
  plt.ylabel('ylabel', fontsize=10)
  
  plt.show()
  </code></pre>