title: Django check session without creating it in datebase
body: <p>I usually check the session like this:  </p>
  
  <pre><code>if request.session.get('var', False):  
    ...
  </code></pre>
  
  <p>The only problem, that if I do that and the session does not exist, django creates it - adds a row to django_session table.<br>
  How can I perform this check without creating the session if it does not exist?</p>