title: numpy `np.array()[None]` behavior
body: <pre><code>import numpy as np  # specify import if you are using it with some other name
  
  np.array([1, 2, 3]) -&gt; array([1, 2, 3])
  
  np.array([1, 2, 3])[None] -&gt; array([[1, 2, 3]])
  </code></pre>
  
  <p>Notice the second lines has one additional dimension. Can someone explain this behavior to me? It's not multiplication. <code>np.array([1, 2, 3])*[None]</code> will raise an error. </p>