title: numpy array indexing: list index and np.array index give different result
body: <p>I am trying to index an np.array using list and <code>np.array</code> indexes.  But they give different result.</p>
  
  <p>Here is an illustration:</p>
  
  <pre><code>import numpy as np 
  x = np.arange(10)
  idx = [[0, 1], [1, 2]]
  x[np.array(idx)]  # returns array([[0, 1], [1, 2]])
  </code></pre>
  
  <p>but straightly apply the list gives error</p>
  
  <pre><code>x[idx]  # raises IndexError: too many indices for array
  </code></pre>
  
  <p>I'm expecting the above returns the same result as using <code>np.array</code> index.
  Any ideas why?</p>
  
  <p>I am using <code>python 3.5</code> and <code>numpy 1.13.1</code>.</p>