title: Django/Python - Check a date is in current week
body: <p>I would like to do something like this:</p>
  
  <pre><code>entries = Entry.objects.filter(created_at__in = current_week())
  </code></pre>
  
  <p>How to make it for good performance. Thanks!</p>
  
  <p>Edit: I still have no idea for <code>current_week()</code> function.</p>