Pythonic update of a `defaultdict`
<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>
