product.py

def product(*iterables):
    if iterables:
        first, *others = iterables
        for x in first:
            for xs in product(*others):
                yield [x] + xs
    else:
        yield []

def product(*iterables):
    if not iterables:
        return
    iters = [iter(xs) for xs in iterables]
    last = len(iters)-1
    i = 0
    row = [0] * len(iters)
    while True:
        try:
            n = next(iters[i])
        except StopIteration:
            if i == 0:
                return
            iters[i] = iter(iterables[i])
            i -= 1
        else:
            row[i] = n
            if i == last:
                yield list(row)
            else:
                i += 1