title: H5py: fast way to save list of list of numpy.ndarray?
body: <p>How can I save and read efficiently a list of list of numpy.ndarray, with h5py? E.g. I want to save/read:</p>
  
  <pre><code>Y = np.arange(3**3).reshape(3,3,3)
  X = [[Y,Y],[Y,Y,Y],[Y]]
  </code></pre>
  
  <p>I am looking for the most efficient (no double loops etc) solution.</p>