title: django - get field which name is dynamic
body: <p>What I need:
  I want to get object details from DB. I use get() function. The problem I have is, that I make in in a function, and one of the arguments is field name as string:</p>
  
  <pre><code>def delete_file_if_changed(id, change, form, model, field_name='image'):
      if change:
          if field_name in form.changed_data:
              old_image = model.objects.get(pk__exact=id)
  </code></pre>
  
  <p>Now - how can I do the thing that I can get old_image.field_name - how to do that?</p>