Actually, wait() calls self._waiters.remove() without holding the lock. But I think it could easily do so after taking the lock (since it takes it anyway before returning).

Also, _waiters should better be a set, since wait() needs the associative behaviour when unregistering a waiter.

notify() would then look like:

for i in range(n):
    try:
        waiter = self._waiters.pop()
    except KeyError:
        break
    waiter.release()

and wait() would look like:

waiter = _allocate_lock()
waiter.acquire()
self._waiters.add(waiter)
self._release_save()
try:
    return waiter.acquire(timeout)
finally:
    self._acquire_restore()
    self._waiters.discard(waiter)