title: Numpy object array of numerical arrays
body: <p>I want to create an array with <code>dtype=np.object</code>, where each element is an array with a numerical type, e.g int or float. For example:</p>
  
  <pre><code>&gt;&gt;&gt; a = np.array([1,2,3])
  &gt;&gt;&gt; b = np.empty(3,dtype=np.object)
  &gt;&gt;&gt; b[0] = a
  &gt;&gt;&gt; b[1] = a
  &gt;&gt;&gt; b[2] = a
  </code></pre>
  
  <p>Creates what I want:</p>
  
  <pre><code>&gt;&gt;&gt; print b.dtype
  object
  
  &gt;&gt;&gt; print b.shape
  (3,)
  
  &gt;&gt;&gt; print b[0].dtype
  int64
  </code></pre>
  
  <p>but I am wondering whether there isn't a way to write lines 3 to 6 in one line (especially since I might want to concatenate 100 arrays). I tried</p>
  
  <pre><code>&gt;&gt;&gt; b = np.array([a,a,a],dtype=np.object)
  </code></pre>
  
  <p>but this actually converts all the elements to np.object:</p>
  
  <pre><code>&gt;&gt;&gt; print b.dtype
  object
  
  &gt;&gt;&gt; print b.shape
  (3,)
  
  &gt;&gt;&gt; print b[0].dtype
  object
  </code></pre>
  
  <p>Does anyone have any ideas how to avoid this?</p>