title: Python Matplotlib plt.show() does not return the figure
body: <p>I remote login a server using <code>ssh -X ***@remote.arizona.edu</code> (This remote server is a Linux system) and tried to make some plots using Python, I had the following errors:</p>
  
  <pre><code>_tkinter.TclError: no display name and no $DISPLAY environment variable
  </code></pre>
  
  <p>Then I fixed this error by the adding the commands before I import any <code>matplotlib</code>:</p>
  
  <pre><code>import matplotlib
  matplotlib.use('Agg')
  matplotlib.matplotlib_fname()
  </code></pre>
  
  <p>Now it runs well. But the problem is that there is no figure displayed even if I had the command <code>plt.show()</code>. My old computer used Ubuntu 16.04 before, there is no such problem. Now I switched to MacBook Air, then I had this issue. It must be some Mac setting issues. Any thoughts to fix this issue?</p>