I need to wait in a script until a certain number of conditions become true?

I know I can roll my own eventing using condition variables and friends, but I don't want to go through all the trouble of implementing it, since some object property changes come from external thread in a wrapped C++ library (Boost.Python), so I can't just hijack __setattr__ in a class and put a condition variable there, which leaves me with either trying to create and signal a Python condition variable from C++, or wrap a native one and wait on it in Python, both of which sound fiddly, needlessly complicated and boring.

Is there an easier way to do it, barring continuous polling of the condition?

Ideally it would be along the lines of

res = wait_until(lambda: some_predicate, timeout)
if (not res):
    print 'timed out'