code: def get_formset_form_class(self):
          
          if self.form_class or self.change_fields:
              params = {'formfield_callback': self.formfield_for_dbfield}
              if self.form_class:
                  fc = self.customize_form_widgets(self.form_class)
                  params['form'] = fc
              if self.change_fields:
                  params['fields'] = self.change_fields
  
              return model_forms.modelform_factory(self.model, **params)
docs: Returns the form class for use in the formset.
  
          If a form_class attribute or change_fields
          is provided then a form will be constructed
          with that. Otherwise None is returned.