* The :mod:`lib2to3` module now emits a :exc:`PendingDeprecationWarning`.

Python 3.9 switched to a PEG parser (see :pep:`617`), and Python 3.10 may

include new language syntax that is not parsable by lib2to3's LL(1) parser.

The ``lib2to3`` module may be removed from the standard library in a future

Python version. Consider third-party alternatives such as `LibCST`_ or

`parso`_.

(Contributed by Carl Meyer in :issue:`40360`.)

.. _LibCST: https://libcst.readthedocs.io/

.. _parso: https://parso.readthedocs.io/