aligned_next.py

iters = [iter(t) for t in [(1, 2), (0, 2), (0, 2, 3)]]


def get(itr):
    try:
        return next(itr)
    except StopIteration:
        return None


def aligned_next(iters, old_min, old_head_values):
    if old_head_values is None:
        head_values = tuple(get(itr) for itr in iters)
    else:
        head_values = tuple(
            get(iters[i]) if (old_head_values[i] is not None and old_head_values[i] == old_min)
            else old_head_values[i]
            for i in range(len(iters))
        )
    non_none_values = [v for v in head_values if v is not None]
    if len(non_none_values) == 0:
        raise StopIteration
    min_value = min(non_none_values)
    return min_value, head_values


min_value = None
head_values = None
while True:
    try:
        min_value, head_values = aligned_next(iters, min_value, head_values)
        print(f"{min_value}, {head_values}")
    except StopIteration:
        break