Python iter() neighbors() function

def neighbors(x: Iterable[_T1], fill_item: _T1 = ...) -> Iterable[Tuple[_T1, _T1]]:
    # def neighbors(x, fill_item = ...):
    values = iter(x)
    for first in values:
        last = first
        for v in values:
            yield last, v
            last = v
        if last is first and fill_item is not Ellipsis:
            yield fill_item, first
            return