Question: what is proper way to define python function as event_trigger?

Hello.

Problem:

1. any attempt to define python function as an event_trigger, i.e.:

CREATE FUNCTION public.verify()
RETURNS event_trigger
LANGUAGE 'plpython3u'
AS $$ print("hello-kitty") $$;

2. fails with message:

ERROR: trigger functions can only be called as triggers

SQL state: 0A000

3. here in the source:

https://github.com/postgres/postgres/blob/master/src/pl/plpython/plpy_procedure.c#L226

Question:

what is proper way to define python function as event_trigger?

Thank you.