Tim, do you remember why Condition.notify() went to great lengths to act as if the lock could be released after the check for self._is_owned()?  

It loops over its own a copy of __waiters, and the __waiters.remove(waiter) code is wrapped in a try/except to detect a situation where __waiters mutated during the release-loop.  I'm presuming that defensive programming was put there for a reason.