code: def get_final_css(self):
          
          default = " ".join(self.get_default_classes())
          defined = self.attrs.get('class', '')
          additional = " ".join(getattr(self, "classes", []))
          non_empty = [test for test in (defined, default, additional) if test]
          final_classes = " ".join(non_empty).strip()
          return final_classes
docs: Returns a final css class concatenated string.