title: Pythonic update of a `defaultdict`
body: <p>What is a more "pythonic" version of this code? (in Python 2.x)</p>
  
  <pre><code>from collections import defaultdict
  dd = defaultdict(list)
  for i in some_list_of_items:
      current_dict = dict_from_an_item(i)
      for (k, v) in current_dict.items():
          dd[k].extend(v)
  </code></pre>
  
  <p>the <code>dict_from_an_item</code> parses an item and returns a dict that contains not nested lists as the values. Something like this    :</p>
  
  <pre><code>{ 'key1': [1, 2, 3],
    'key2': [2, 3, 4],
    'key3': [3, 4, 5, 6, 7, 8]}
  </code></pre>