code: def _family_id_to_superclass(self, family_id):
          
          for family in [XBlock, XBlockAside]:
              if family_id == family.entry_point:
                  return family
          raise ValueError('No such family: {}'.format(family_id))
docs: Temporary hardcoded mapping from serialized family id to either `class :XBlock:` or `:XBlockAside`