Source code for libcst._flatten_sentinel

# Copyright (c) Meta Platforms, Inc. and affiliates.
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.

import sys

# PEP 585
if sys.version_info < (3, 9):
    from typing import Iterable, Sequence
    from import Iterable, Sequence

from libcst._types import CSTNodeT_co

[docs]class FlattenSentinel(Sequence[CSTNodeT_co]): """ A :class:`FlattenSentinel` may be returned by a :meth:`CSTTransformer.on_leave` method when one wants to replace a node with multiple nodes. The replaced node must be contained in a `Sequence` attribute such as :attr:`~libcst.Module.body`. This is generally the case for :class:`~libcst.BaseStatement` and :class:`~libcst.BaseSmallStatement`. For example to insert a print before every return:: def leave_Return( self, original_node: cst.Return, updated_node: cst.Return ) -> Union[cst.Return, cst.RemovalSentinel, cst.FlattenSentinel[cst.BaseSmallStatement]]: log_stmt = cst.Expr(cst.parse_expression("print('returning')")) return cst.FlattenSentinel([log_stmt, updated_node]) Returning an empty :class:`FlattenSentinel` is equivalent to returning :attr:`cst.RemovalSentinel.REMOVE` and is subject to its requirements. """ nodes: Sequence[CSTNodeT_co] def __init__(self, nodes: Iterable[CSTNodeT_co]) -> None: self.nodes = tuple(nodes) def __getitem__(self, idx: int) -> CSTNodeT_co: return self.nodes[idx] def __len__(self) -> int: return len(self.nodes)