title: python bar plot from list of tuples
body: <p>Very newbie question:</p>
  
  <p>I need to draw a bar plot from a list of tuples.  The first element is a name (categorical) for the x axis, the second element is float type (for the y axis).  I'd also like to order the bars in descending order, and add a trendline.  Here is some sample code:</p>
  
  <pre><code>In [20]: popularity_data
  Out[20]: 
  [('Unknown', 10.0),
   (u'Drew E.', 240.0),
   (u'Anthony P.', 240.0),
   (u'Thomas H.', 220.0),
   (u'Ranae J.', 150.0),
   (u'Robert T.', 120.0),
   (u'Li Yan M.', 80.0),
   (u'Raph D.', 210.0)]
  </code></pre>