title: Left tick marks remain in matplotlib despite call to tick_params and use of NullLocator
body: <p>I've been struggling to remove the left tick marks from a matplotlib plot which has two subplots which share the x-axis.</p>
  
  <p>If I just start with one plot, things behave as I would expect:</p>
  
  <pre><code>X = np.linspace(0, 2 * np.pi, 100)
  Y = np.sin(X)
  Z = np.sin(2 * X)
  
  fig, ax1 = plt.subplots()
  
  ax1.set_ylim([-1.1, 1.1])
  
  ax1.spines['top'].set_visible(False)
  ax1.spines['left'].set_visible(False)
  ax1.spines['right'].set_visible(False)
  
  ax1.tick_params(axis='both',
                  which='both',
                  bottom='off',
                  top='off',
                  left='off',
                  right='off')
  
  ax1.plot(X, Y, color='b')
  </code></pre>
  
  <p>yields:
  <a href="http://i.stack.imgur.com/RqNiM.png" rel="nofollow">No left ticks, all is well</a></p>
  
  <p>If I try to use <code>.twinx()</code> to make another plot that shares the same y-axis and use the same methods I used on <code>ax1</code>, then the left ticks return:</p>
  
  <pre><code>... continuing the block above...
  
  ax2 = ax1.twinx()
  ax2.spines['top'].set_visible(False)
  ax2.spines['left'].set_visible(False)
  ax2.spines['right'].set_visible(False)
  
  ax2.tick_params(axis='both',
                  which='both',
                  bottom='off',
                  top='off',
                  left='off',
                  right='off')
  
  ax2.plot(X, Z, color='r')
  </code></pre>
  
  <p>yields:
  <a href="http://i.stack.imgur.com/G5gOk.png" rel="nofollow">The left ticks are back</a></p>
  
  <p>I'm probably missing something simple, but I've been reading through documentation, playing with code, and looking through other posts to no avail.</p>
  
  <p>Any help would be greatly appreciated.</p>
  
  <p>EDIT: including <code>ax2.yaxis.set_major_locator(plt.NullLocator())</code> still doesn't get rid of the left ticks.</p>