def merge2(iter1,iter2):
   """ on input iter1, iter2, two non-empty sorted iterators, not
    necessarily infinite, produces the sorted merge of the two iterators"""

    left=next(iter1)
    right=next(iter2)
    while True:
        if left<right:
            yield(left)
            try:
                left=next(iter1)
            except StopIteration:  # iter1 is exhausted
                yield(right)          # in my question I refer to this yield
                for right in iter2:
                    yield(right)
                break                    
        else:
            yield(right)
            try:
                right=next(iter2)
            except StopIteration:  # iter2 is exhausted
                yield(left)
                for left in iter1:
                    yield(left)
                break