I need to merge two iterators. I wrote this function:

```
def merge_no_repeat(iter1, iter2, key=None):
    """
    a = iter([(2, 'a'), (4, 'a'), (6, 'a')])
    b = iter([(1, 'b'), (2, 'b'), (3, 'b'), (4, 'b'), (5, 'b'), (6, 'b'), (7, 'b'), (8, 'b')])
    key = lambda item: item[0]
    fusion_no_repeat(a, b, key) ->
                iter([(1, 'b'), (2, 'a'), (3, 'b'), (4, 'a'), (5, 'b'), (6, 'a'), (7, 'b'), (8, 'b')])
    :param iter1: sorted iterator
    :param iter2: sorted iterator
    :param key: lambda get sorted key, default: lambda x: x
    :return: merged iterator
    """
    if key is None:
        key = lambda x: x
    element1 = next(iter1, None)
    element2 = next(iter2, None)
    while element1 is not None or element2 is not None:
        if element1 is None:
            yield element2
            element2 = next(iter2, None)
        elif element2 is None:
            yield element1
            element1 = next(iter1, None)
        elif key(element1) > key(element2):
            yield element2
            element2 = next(iter2, None)
        elif key(element1) == key(element2):
            yield element1
            element1 = next(iter1, None)
            element2 = next(iter2, None)
        elif key(element1) < key(element2):
            yield element1
            element1 = next(iter1, None)

```

This function works. But I think it's too complicated. Is it possible to make this function easiest using *Python Standard Libraries*?