code: def form_lines_valid(self, form):
          
          handled = 0
          for inner_form in form:
              if not inner_form.cleaned_data.get(formsets.DELETION_FIELD_NAME):
                  handled += 1
                  self.handle_inner_form(inner_form)
  
          self.log_and_notify_lines(handled)
          return http.HttpResponseRedirect(self.get_success_url())
docs: Handle a valid LineFormSet.