Checked Python izip variant.

izip_checked.py

class izip_checked(object):
    def __init__(self, *args):
        self._iterators = map(iter, args)

    def __iter__(self):
        if self._iterators:
            return self
        return iter([])

    def next(self):
        results = []
        stop = False

        for iterator in self._iterators:
            try:
                results.append(iterator.next())
                if stop:
                    raise Exception("Later iterators succeeded, returned {}.".format(results))
            except StopIteration:
                if results:
                    raise Exception("Earlier iterators succeeded, returned {}.".format(results))
                stop = True

        if stop:
            raise StopIteration()

        return tuple(results)