title: Creating a defaultdict with empty numpy array
body: <p>I'm wondering if there's a more clever way to create a default dict from collections.
  The dict should have an empty numpy ndarray as default value.</p>
  
  <p>My best result is so far:</p>
  
  <pre><code>import collections
  d = collections.defaultdict(lambda: numpy.ndarray(0))
  </code></pre>
  
  <p>However, i'm wondering if there's a possibility to skip the lambda term and create the dict in a more direct way. Like: </p>
  
  <pre><code>d = collections.defaultdict(numpy.ndarray(0))  # &lt;- Nice and short - but not callable
  </code></pre>