title: Python Slice Notation with Comma/List
body: <p>I have come across some python code with slice notation that I am having trouble figuring out.
  It looks like slice notation but uses a comma and a list:  </p>
  
  <pre><code>list[:, [1, 2, 3]]
  </code></pre>
  
  <p>Is this syntax valid? If so what does it do?</p>
  
  <p><b>edit</b> looks like it is a 2D numpy array</p>