title: global variables not updated
body: <p>I am new here and probably this is super obvious, but I don't get it:
  I wanna save the clicked coordinates (coords) to work with them aferwards, somehow this doesn't work. I am still on Python 2.7 btw. </p>
  
  <p>thanks in advance!</p>
  
  <pre><code>import matplotlib.pyplot as plt
  
  plt.close('all')
  coords=[]
  
  
  # Simple mouse click function to store coordinates
  def onclick(event):
      global coords, xi,yi
      xi,yi =event.xdata, event.ydata
      coords.append((xi,yi))
      if len(coords) == 2:
          fig.canvas.mpl_disconnect(cid)
          plt.close(1)
  
  
  
      return coords, xi , yi 
  
  
  
  
  x = np.arange(-10,10)
  y = x**2
  
  fig = plt.figure(1)
  ax = fig.add_subplot(111)
  ax.plot(x,y)
  plt.show(1)
  
  
  # Call click func
  cid = fig.canvas.mpl_connect('button_press_event', onclick)
  print coords
  
  
  </code></pre>