title: How to see if the user chose a element in a list (python)
body: <p>I'm trying to use the following code :</p>
  
  <pre><code>blosum = input("pick a matrix:")
  x = [30, 40, 50, 100, 75, 70]
  while blosum not in x :
      blosum = raw_input("Incorrect, pick a valid matrix:")
  print ('ok')    
  </code></pre>
  
  <p>I want it to decide whether the user chose one of the options of the list. If the user chose one of them, then the program should keep running, otherwise, it keeps telling the user to pick a valid matrix. But it doesn't work, why?</p>