lazy_product.py

from itertools import product

def lazy_product(*iterables):
    iters = [[i.__iter__(), [], False] for i in iterables]
    def _p_next(i, il, _):
        z = i.__next__()
        il.append(z)
        return z
    s = True
    while s:
        s = False
        for i in (x for x in iters if not x[2]):
            try:
                v = _p_next(*i)
                yield from product(*(j[1] if j is not i else [v] for j in iters))
                s = True
            except StopIteration:
                i[2] = True