title: efficiently knowing if intersection of two list is empty or not, in python
body: <p>Suppose I have two lists, L and M. Now I want to know if they share an element.
  Which would be the fastest way of asking (in python) if they share an element?
  I don't care which elements they share, or how many, just if they share or not.</p>
  
  <p>For example, in this case  </p>
  
  <pre><code>L = [1,2,3,4,5,6]
  M = [8,9,10]
  </code></pre>
  
  <p>I should get False, and here:</p>
  
  <pre><code>L = [1,2,3,4,5,6]
  M = [5,6,7]
  </code></pre>
  
  <p>I should get True.</p>
  
  <p>I hope the question's clear.
  Thanks!</p>
  
  <p>Manuel</p>