def next(self):
        if self.counter == 0 and self.used:
            raise StopIteration()
        try:
            return self.waiters.get().wait()
        finally:
            self.counter -= 1
Check to see if a stack exists.
dataset/ETHPy150Open veegee/guv/guv/greenpool.py/GreenPile.next--crossover with--dataset/ETHPy150Open saltstack/salt/salt/modules/boto_cfn.py/exists