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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def closest_common_ancestor(self, other):
 """ Find the common ancestor between this history node and 'other'. :param other: the PathHistory to find a common ancestor with. :return: the common ancestor SimStateHistory, or None if there isn't one """

        our_history_iter = reversed(HistoryIter(self))
        their_history_iter = reversed(HistoryIter(other))
        sofar = set()

        while True:
            our_done = False
            their_done = False

            try:
                our_next = next(our_history_iter)
                if our_next in sofar:
                    # we found it!
                    return our_next
                sofar.add(our_next)
            except StopIteration:
                # we ran out of items during iteration
                our_done = True

            try:
                their_next = next(their_history_iter)
                if their_next in sofar:
                    # we found it!
                    return their_next
                sofar.add(their_next)
            except StopIteration:
                # we ran out of items during iteration
                their_done = True

            # if we ran out of both lists, there's no common ancestor
            if our_done and their_done:
                return None