title: Pythonic way to find elementa of a python list that are not contained in another python list
body: <p>I am trying to find a faster solution to what I have now. My problem consists of creating a python list derived from 2 other lists. List_a has many elements, list_b has even more elements, some in common with list_a.</p>
  
  <p>This is what I have:</p>
  
  <pre><code>list_a = [a huge python list with over 100,000 elements ]
  list_b = [a huge python list with over 1,000,00 elements]
  </code></pre>
  
  <p>My solution:</p>
  
  <pre><code>list_c = []
  for item in list_a:
      if item not in list_b:
          list_c.append(item)
  </code></pre>
  
  <p>It works, but it is very, very slow. Is there a way to solve this faster?</p>