title: Interactive plotting mode pl.ion() not working
body: <p>I have the following in my <code>matplotlibrc</code>:</p>
  <pre><code>backend : QT4Agg
  backend.qt4 : PySide
  </code></pre>
  <p>If I try the following:</p>
  <pre><code>import pylab as pl
  pl.ion()
  pl.plot(xrange(10))
  pl.show()
  pl.draw()
  </code></pre>
  <p>Nothing happens. No window is opened.</p>
  <p><strong>But</strong> if I do:</p>
  <pre><code>import pylab as pl
  pl.ioff()
  pl.plot(xrange(10))
  pl.show()
  </code></pre>
  <p>I can see the window and the plot correctly.</p>
  <p>Ho can I fix this? I am using <a href="https://store.continuum.io/cshop/anaconda/" rel="nofollow noreferrer">Anaconda</a>'s distribution on Linux 64 bit.</p>
  <h2>Update:</h2>
  <p>I have reproduced the behavior above in two different ways:</p>
  <ol>
  <li>From the shell (e.g. bash), <code>&gt; python program.py</code></li>
  <li>Starting <code>ipython</code> as <code>&gt; ipython</code>, and then <code>run program.py</code></li>
  </ol>