Most pythonic means to find out if an element from one list is not a member of another list
<blockquote>
  <p><strong>Possible Duplicate:</strong><br>
  <a href="http://stackoverflow.com/questions/5305164/get-difference-from-2-lists-python">Get difference from 2 lists. Python</a>  </p>
</blockquote>



<p>I have two lists</p>

<pre><code>rt = [1,2,3]
dp = [1,2]
</code></pre>

<p>What is the most pythonic way to find out that in the <code>rt</code> list that <code>3</code> is not a element of the <code>dp</code> list?</p>
