Python - intersect a dict and list
<p>Given the following data structures ,what is the most efficient way to find out the intersection -  keys which are common to both the data structures.  </p>

<pre><code>dict1 = {'2A':'....','3A':'....','4B':.....}  
list1 = [......,'2A','4B'.....]

Expected output = ['2A','4B']
</code></pre>

<p>I am fine to organize the list(not dict1) into any other data-structure if that yields a faster output too.
Since this lookup has 2 be done for a large number of dicts - speed is vital.</p>
