The current documentation says it returns None if the name is not found, but (GH-26785) (GH-27371)

the implementation uses [] and will raise KeyError instead.

Noticed by @srittau in python/typeshed@5659.
(cherry picked from commit f22737abfa07605f4ed1a99cfa97a26520b6c5c2)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>