title: NumPy append vs Python append
body: <p>In Python I can append to an empty array like:</p>
  
  <pre><code>&gt;&gt;&gt; a = []
  &gt;&gt;&gt; a.append([1,2,3])
  &gt;&gt;&gt; a.append([1,2,3])
  &gt;&gt;&gt; a
  [[1, 2, 3], [1, 2, 3]]
  </code></pre>
  
  <p>How can I do the same in NumPy? <code>np.append</code> flattens the array, unfortunately (and I need to have an empty array at the beginning).</p>