title: Python != operation vs "is not"
body: <p>In a comment on <a href="https://stackoverflow.com/questions/2079786/caching-sitemaps-in-django">this question</a>, I saw a statement that recommended using</p>
  
  <pre><code>result is not None
  </code></pre>
  
  <p>vs</p>
  
  <pre><code>result != None
  </code></pre>
  
  <p>I was wondering what the difference is, and why one might be recommended over the other?</p>