code: def wants(cls, *service_names):
          
          def _decorator(cls_):                                # pylint: disable=missing-docstring
              for service_name in service_names:
                  cls_._services_requested[service_name] = "want"  # pylint: disable=protected-access
              return cls_
          return _decorator
docs: A class decorator to indicate that an XBlock class wants particular services.