def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        else:
            ret = self[key] = self.default_factory(name=key)
            return ret
def reorder_item(self, item, new_position):
    orig_position = self._get_item_position(item)
    processed_new_position = super().reorder_item(item, new_position)