def _AppendTokenSubtype(self, node, subtype, force=True):
    pytree_utils.AppendNodeAnnotation(node, pytree_utils.Annotation.SUBTYPE,
                                      subtype)
Append the token's subtype only if it's not already set.
dataset/ETHPy150Open google/yapf/yapf/yapflib/subtype_assigner.py/_SubtypeAssigner._AppendTokenSubtype