title: matplotlib:plot a line closed
body: <p>I plot a figure as below:</p>
  
  <pre><code>plt.plot(lon,lat,'ro-')
  plt.show()
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/P5mJx.png" alt="enter image description here"></p>
  
  <p>but the lines aren't closed.
  How can I make them closed as polygons?
  thank you</p>