title: Finding intersection/difference between python lists
body: <p>I have two python lists:</p>
  
  <pre><code>a = [('when', 3), ('why', 4), ('throw', 9), ('send', 15), ('you', 1)]
  
  b = ['the', 'when', 'send', 'we', 'us']
  </code></pre>
  
  <p>I need to filter out all the elements from a that are similar to those in b. Like in this case, I should get:</p>
  
  <pre><code>c = [('why', 4), ('throw', 9), ('you', 1)]
  </code></pre>
  
  <p>What should be the most effective way?</p>