The one I know is pypy: bool(x) always return one of the two prebuilt singletons 
(doubletons?).

The docs explicitly mention "If lock is True...", "If lock is False...":
http://docs.python.org/library/multiprocessing.html#multiprocessing.sharedctypes.Value

I fear that testing the boolean value of the lock variable may have undesired effect; if 
even the main multiprocessing.RLock object has a _is_zero() method (that seems to return 
whether the lock is held or not), it is very possible that other implementations choose 
__nonzero__ for this.