is being run itself, either from inside the listener or from a
concurrent thread, now raises a RuntimeError, as the collection used is
now an instance of ``colletions.deque()`` and does not support changes
while being iterated.  Previously, a plain Python list was used where
removal from inside the event itself would produce silent failures.
fixes #3163

sqlalchemy/orm, sqlalchemy/event, sqlalchemy/testing

to get all flake8 passing

event.listen and event.listen_for have a kwarg once added in 0.9.4 (not 0.9.3) CHANGELOG agrees with this as well. (as does my manual testing)

and :func:`.event.listens_for`.  This is a convenience feature which
will wrap the given listener such that it is only invoked once.

if the given target/event/fn is set up to listen.
- repair mutable package which is doing some conditional event listening