title: Unusual behaviour of pick_event in a matplotlib
body: <p>When fig.canvas.draw() is used in onclick function, it doesn't wait for onclick event, and it comes out of the function. How to make it work continuously, so that label can be displayed every time when  clicked on the pie chart.</p>
  
  <pre><code>import matplotlib.pyplot as plt
  labels = ['Beans', 'Squash', 'Corn']
  def main():
      # Make an example pie plot
      fig = plt.figure()
      ax = fig.add_subplot(111)
  
      #labels = ['Beans', 'Squash', 'Corn']
      wedges, plt_labels = ax.pie([20, 40, 60], labels=labels)
      ax.axis('equal')
  
      make_picker(fig, wedges)
      plt.show()
  
  def make_picker(fig, wedges):
  
      def onclick(event):
          print event.__class__
          wedge = event.artist
          label = wedge.get_label()
          print label
          fig.canvas.figure.clf() 
          ax=fig.add_subplot(111)
          wedges, plt_labels = ax.pie([50, 100, 60],labels=labels)
          fig.canvas.draw()
  
      # Make wedges selectable
      for wedge in wedges:
          wedge.set_picker(True)
  
      fig.canvas.mpl_connect('pick_event', onclick)
  
  if __name__ == '__main__':
      main()
  </code></pre>