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 current_label_start(self):
        if self.current_label and self.message:
            return self.message.get_label_range(self.current_label, self.proto_view, False)[0]
        else:
            return -1