How can two default dictionaries of lists be merged into one
<pre><code>the d1 is  defaultdict(&lt;type 'list'&gt;, {'A': [4, 4, 4, 4], 'S': [1]})
the d2 is  defaultdict(&lt;type 'list'&gt;, {'A': [4, 4, 4], 'B': [2], '[]': [4, 4]})
</code></pre>

<p>How to merge these two dictionaries into one?</p>

<p>The expected output should be </p>

<pre><code>the d3 is  defaultdict(&lt;type 'list'&gt;, {'A': [4], 'B': [2], 'S':[1] ,'[]': [4]})
</code></pre>

<p>In the resultant dictionary the multiple values should be made into one</p>
