title: Matplotlib ion() function fails to be interactive
body: <p>I have problem with interactive feature of Matplotlib. I ran the following program and received a freezing empty graph window.</p>
  
  <pre><code>import matplotlib.pyplot as plt
  import numpy as np
  
  plt.ion()
  x = np.arange(0, 4*np.pi, 0.1)
  y = [np.sin(i) for i in x]
  plt.plot(x, y, 'g-', linewidth=1.5, markersize=4)
  plt.show()
  </code></pre>
  
  <p>If I removed 'plt.ion()' statement, then it worked just fine. I use IDLE and the Matplotlib version 1.2.x package is installed in Python 3.2.2. </p>
  
  <p>I expect it to be interactive, but instead I got an unfriendly non-interactive window. Can someone shed some light of what I am missing? Thank you in advance.</p>