title: Multiple interact() commands duplicate widgets in IPython
body: <p>I am using an IPython Jupyter notebook. In the following situation, I call a function using <code>interact()</code>, which in turns calls a second function again using <code>interact()</code>.</p>
  
  <pre><code>def fun1(dataset_id):
       dataset = read_dataset(dataset_id)
       interact(fun2, data=dataset, var=(0,dataset.property,0.1))
  
  def fun2(data, var):
       # something
  
  interact(fun1, dataset_id=(0,5,1))
  </code></pre>
  
  <p>When first running this, it display 2 slider widgets: one for <code>dataset_id</code>, and one for the variable <code>var</code>. But if I vary the <code>dataset_id</code> slider once, a second slider for <code>var</code> is added below the first <code>var</code> slider, so now I have 3 sliders in total. How can I avoid this?</p>