zip_longest_impl.py

# Don’t use this, use itertools.zip_longest() instead!
def alternate_all(*args):
    ls = [iter(i) for i in args]
    stops = 0 # cheat and get 9 LOC by making this a keyword argument
    while stops != len(ls):
        stops = 0
        for l in ls:
            try:
                yield next(l)
            except StopIteration:
                stops += 1