title: Numpy iterator on array do not work as expected
body: <p>I want to declare an array of object and later to include arrays in it. I can do it this way:</p>
  
  <pre><code>import numpy as np    
  v = np.empty([2,2], dtype=object)
  for i in range(len(v.flat)):
    v.flat[i] = np.ones([3])
  </code></pre>
  
  <p>But since Numpy has iterators, I wanted to use them:</p>
  
  <pre><code>v = np.empty([2,2], dtype=object)
  for i in np.nditer(v, flags=['refs_ok'],op_flags=['readwrite']):
    i[...] = np.ones([3])
  </code></pre>
  
  <p>and the message is:</p>
  
  <pre><code>ValueError: could not broadcast input array from shape (3) into shape()
  </code></pre>
  
  <p>Can someone explain my how to do it correctly?</p>
  
  <p>TIA</p>