title: Matplotlib plot is a no-show
body: <p>When I run this code</p>
  
  <pre><code>import pandas as pd
  import numpy as np
  def add_prop(group):
      births = group.births.astype(float)
      group['prop'] = births/births.sum()
      return group
  
  pieces = []
  columns = ['name', 'sex', 'births']
  
  for year in range(1880, 2012):
      path = 'yob%d.txt' % year
      frame = pd.read_csv(path, names = columns)
      frame['year'] = year
      pieces.append(frame)
      names = pd.concat(pieces, ignore_index = True)
  
  total_births = names.pivot_table('births', rows = 'year', cols = 'sex', aggfunc = sum)
  total_births.plot(title = 'Total Births by sex and year')
  </code></pre>
  
  <p>I get no plot.  This is from Wes McKinney's book on using Python for data analysis.
  Can anyone point me in the right direction?</p>