title: Django pre_save signal
body: <p>I needed to be able to change my model data before it's saved, so I considered using pre_save handler to be the best option:</p>
  
  <pre><code>@receiver(pre_save, weak = False)
  def pre_category_save(sender, **kwargs):
      if kwargs['instance'].tags is None:
          kwargs['instance'].tags = kwargs['instance'].__unicode__().replace(' -&gt; ', ', ')
  </code></pre>
  
  <p>Under the instance key of kwargs I expected to find the actual model instance I'm saving, but instead I got an object of LogEntry class - that's the cause why my function fails returning this error: 'LogEntry' object has no attribute 'tags'. So - how can I fix that? Checking if instance has attribute tags is not a solution, because I always get only logentry object. I can eventually overload Model.save method, though I'd rather not do this.</p>