import rx

once = False


def nope(i):
    global once
    print('try', i)
    if i == 2 and not once:
        once = True
        raise ValueError(i)
    return i


s = rx.subjects.Subject()

s.map(nope).retry().subscribe(print)


s.on_next(1)
s.on_next(2)
s.on_next(3)