bpo-39176: Improve error message for 'named assignment' (GH-17777) (GH-17778)

(cherry picked from commit 37143a8e3b2e9245d52f4ddebbdd1c6121c96884)

Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>

Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>
3 files changed