title: Django csv export
body: <p>I have the following csv export function to export model information in csv file. But I am trying to figure out how to show outputs from functions in the model. So the csv export function shows all the fields in the model (fields in the table) but not outputs from functions in the model..</p>
  
  <p>So if I have the following:</p>
  
  <pre><code>def avg_tag(self, obj):
      bids = Bid.objects.active(user=obj.user.id)
      return bids.aggregate(average_price=Avg('list_price'))['average_price']
  </code></pre>
  
  <p>in the model</p>
  
  <p>It does not get the output from that function.</p>
  
  <p>Here is the csv export function action:</p>
  
  <pre><code>def export_select_fields_csv_action(description="Export selected objects",
                       fields=None, exclude=None, header=True):
  def export_as_csv(modeladmin, request, queryset):
      """
      Generic csv export admin action.
      based on http://djangosnippets.org/snippets/1697/
      """
      opts = modeladmin.model._meta
      field_names = [field.name for field in opts.fields]
      labels = []
      if exclude:
          field_names = [v for v in field_names if v not in exclude]
      elif fields:
          field_names = [k for k, v in fields if k in field_names]
          labels = [v for k, v in fields if k in field_names]
  
      response = HttpResponse(mimetype='text/csv')
      response['Content-Disposition'] = ('attachment; filename=%s.csv'
          % unicode(opts).replace('.', '_'))
  
      writer = csv.writer(response)
      if header:
          if labels:
              writer.writerow(labels)
          else:
              writer.writerow(field_names)
      for obj in queryset:
          writer.writerow([unicode(getattr(obj, field)).encode('utf-8')
              for field in field_names])
      return response
  export_as_csv.short_description = description
  return export_as_csv
  </code></pre>
  
  <p>How can I change the function above so that the outputs from functions in the model are outputted in the csv? Thanks!</p>