title: Error "AttributeError: 'NoneType' object has no attribute 'kernel' when using simply vpython
body: <p>I'm just starting to try and use vpython, hoping to eventually use it to simulate an elliptical or parabolic orbit. I downloaded the module and tried to generate a simple sphere, and when I do so I get the above error. As far as I can tell, I have defined/called the function correctly. Here is my code</p>
  
  <pre><code>from vpython import *
  Sun = sphere(pos=(0,0,0), radius =0.5))
  </code></pre>