title: How to find a missing number from a list?
body: <p>How do I find the missing number from a sorted list the pythonic way?</p>
  
  <pre><code>a=[1,2,3,4,5,7,8,9,10]
  </code></pre>
  
  <p>I have come across this <a href="https://codereview.stackexchange.com/questions/24520/finding-missing-items-in-an-int-list/">post</a> but is there a more and efficient way to do this?</p>