title: In numpy, why multi dimension array d[0][0:2][0][0] returning not two elements
body: <pre><code>In [136]: d = np.ones((1,2,3,4))
  
  In [167]: d[0][0][0:2][0]
  Out[167]: array([ 1.,  1.,  1.,  1.])
  </code></pre>
  
  <p>as shown above, why it's not returning exactly 2 elements</p>