title: how to remove line connecting discontinued point in matplotlib.pyplot.plot
body: <p>I have a dataframe which has one column shows price, and its index is datetime.</p>
  
  <pre><code>2018-09-18T02:29:56.5   524.6
  2018-09-18T02:29:57.0   524.6
  2018-09-18T02:29:57.5   524.8
  2018-09-18T02:29:59.0   525.1
  2018-09-18T02:29:59.5   525.1
  2018-09-18T02:30:00.0   524.8
  2018-09-19T21:00:00.5   527.1
  2018-09-19T21:00:01.0   527.1
  2018-09-19T21:00:01.5   527.3
  2018-09-19T21:00:02.0   527.7
  2018-09-19T21:00:02.5   527.5
  2018-09-19T21:00:03.0   527.6
  2018-09-19T21:00:03.5   527.4
  </code></pre>
  
  <p>im trying to plot the timeplot by <code>matplotlib.pyplot.plot(df)</code>.
  It gives a plot but with a long straight line connecting the discontinued datapoint (last data point on 2018-09-18T02:30:00.0 and the first data point on 2018-09-19T21:00:00.5). Is there a way to remove the connecting line between the data point gap?</p>