Cartesian Product

v1.js

function* cartesianProduct(...iterables) {
    const pools = iterables.map(function(iterable) {
        const pool = Array.from(iterable);

        return {pool, length: pool.length, counter: 0};
    });
    let iterations = pools.reduce(
        (total, {length}) => total * length,
        1
    );
    while(iterations--) {
        yield pools.map(({counter, pool}) => pool[counter]);

        for(const pool of pools) {
            pool.counter++;
            if(pool.counter < pool.length) {
                break;
            }
            pool.counter = 0;
        }
    }
}

v2.py

import functools
import itertools
import operator

import pytest

def product(*iterables):
    pools = [tuple(iterable) for iterable in iterables]
    iterations = functools.reduce(operator.mul, map(len, pools))

    for i in range(iterations):
        result = []
        for pool in pools:
            result.append(pool[i % len(pool)])
            i //= len(pool)
        yield tuple(result)

class CartesianProduct:
    def __init__(self, *iterables):
        self.pools = [tuple(iterable) for iterable in iterables]
    
    def __len__(self):
        return functools.reduce(
            operator.mul,
            map(len, self.pools)
        )
    
    def __getitem__(self, idx):
        result = []
        for pool in self.pools:
            result.append(pool[idx % len(pool)])
            idx = idx // len(pool)
        return tuple(result)
    
    def __iter__(self):
        for i in range(len(self)):
            yield self[i]


@pytest.mark.parametrize('a', [
    ([1, 2], [3, 4]),
    ([1], [2]),
    ([1, 2, 3], [1, 2]),
    ([1, 2], [3, 4], [5, 6]),
    ([1], [2, 3], [4, 5, 6], [7, 8, 9, 10]),
    ([1, 2, 3, 4], [5, 6, 7], [8, 9], [10]),
])
def test_product(a):

    assert sorted(itertools.product(*a)) == sorted(product(*a))


@pytest.mark.parametrize('a', [
    ([1, 2], [3, 4]),
    ([1], [2]),
    ([1, 2, 3], [1, 2]),
    ([1, 2], [3, 4], [5, 6]),
    ([1], [2, 3], [4, 5, 6], [7, 8, 9, 10]),
    ([1, 2, 3, 4], [5, 6, 7], [8, 9], [10]),
])
def test_cartesianproduct(a):
    cart_prod = CartesianProduct(*a)
    assert sorted(itertools.product(*a)) == sorted(cart_prod)