class RangeIterator(object):
    def __init__(self, start, end):
        self.i = start
        self.end = end
    def __next__(self):
        if self.i >= self.end:
            raise StopIteration(self.i)
        i = self.i
        self.i += 1
        return i
class Range(object):
    def __init__(self, start, end):
        self.start = start
        self.end = end
    def __iter__(self):
        return RangeIterator(self.start, self.end)
r = Range(3, 10)
try:
    s, t = iter(r), iter(r)
    while True:
        print(next(s), next(t))
except StopIteration as e:
    print('Caught:', repr(e))