Recursive Cartesian Product

A recursive approach to Python's iterative method for the Cartesian product:

def product(*args):
    res = []
    product_helper([], args, 0, res)
    return res

def product_helper(prefix, pools, offset, res):
    if offset >= len(pools):

    pool = pools[offset]

    for i in range(len(pool)):
        product_helper(prefix + [pool[i]], pools, offset + 1, res)

if __name__ == '__main__':
    import itertools
    L = ['abc', 'def']
    assert product(*L) == list(itertools.product(*L))