code: def cls_sets(cls, wanted_cls, registered=True):
      
      sets = []
      for attr in dir(cls):
          if attr.startswith('_'):
              continue
          val = getattr(cls, attr, None)
          if not isinstance(val, wanted_cls):
              continue
          if (not registered) and getattr(val, '_registered', False):
              continue
          sets.append(val)
      return sets
docs: Return a list of all `wanted_cls` attributes in this
          class, where `wanted_cls` is the desired attribute type.