          # When the ModelForm is passed an instance, that instance's current values are
          # inserted as 'initial' data in each Field.
          f = RoykoForm(auto_id=False, instance=self.w_royko)
          self.assertHTMLEqual(
              six.text_type(f),
              '''<tr><th>Name:</th><td><input type="text" name="name" value="Mike Royko" maxlength="50" required /><br />
              <span class="helptext">Use both first and last names.</span></td></tr>'''
          )
  
          art = Article.objects.create(
 
</s> remove             six.text_type(f),
 </s> add             str(f), </s> remove             six.text_type(f),
 </s> add             str(f), </s> remove             six.text_type(CustomFieldForExclusionForm()),
 </s> add             str(CustomFieldForExclusionForm()), </s> remove             six.text_type(f.media),
 </s> add             str(f.media), </s> remove             six.text_type(CategoryForm()),
 </s> add             str(CategoryForm()),
            str(f),
          # When the ModelForm is passed an instance, that instance's current values are
          # inserted as 'initial' data in each Field.
          f = RoykoForm(auto_id=False, instance=self.w_royko)
          self.assertHTMLEqual(
            str(f),
              '''<tr><th>Name:</th><td><input type="text" name="name" value="Mike Royko" maxlength="50" required /><br />
              <span class="helptext">Use both first and last names.</span></td></tr>'''
          )
  
          art = Article.objects.create(
keep keep keep keep replace keep keep keep keep keep
 Refs #23919 -- Removed six.<various>_types usage

Thanks Tim Graham and Simon Charette for the reviews. 
tests/model_forms/tests.py