title: matplotlib y axis labels disappearing with fontsize change
body: <p>I have the following code to plot the contents of a dataframe.</p>
  
  <p>Using pandas and matplotlib:</p>
  
  <pre><code>thedata = {'2013':[0.0,0.0]
            ,'2014':[0.0,0.0]
            ,'2015':[0.0,0.0]
            ,'2016':[1,0.0]
            ,'2017':[0.0,0.0]
            ,'2018':[1,0.0]}
  
  my_df = pd.DataFrame(thedata, index=['Green cars','Red cars'])
  
      plt.figure(figsize=(7,3))
      my_ax = plt.gca()
      my_ax.clear()
      my_ax.yaxis.set_major_locator(MaxNLocator(integer=True))
  
      my_df.transpose().plot(kind='bar'
                  , stacked=True  
                  , ax=my_ax
                  ).grid(True,'major','y')
  
      my_ax.legend(loc=9, bbox_to_anchor=(0.5, -0.1), frameon=False, ncol=2, fontsize=12 )
      plt.title('All the cars', fontsize = 12 )
      my_ax.set_xticklabels(my_ax.get_xticklabels(),rotation='horizontal', fontsize=12)
  #     my_ax.set_yticklabels(my_ax.get_yticklabels(),fontsize=12)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/vt6h6.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/vt6h6.jpg" alt="The dataframe and the output"></a></p>
  
  <p>The last line is commented out in order to get the output displayed.  I want to increase the font size of the y axis labels to be the same as the x, but when i un-comment that line and run it, the y axis labels just disappear and nothing is displayed there.</p>
  
  <p>Why is this happening and how do I fix it?</p>
  
  <p>Edit: - create the dataframe; pandas 0.23.0, matplotlib 2.2.2</p>