>>> list(itertools.product(*arrays))
[(-1, -2, -3), (-1, -2, 3), (-1, 2, -3), (-1, 2, 3), (1, -2, -3), (1, -2, 3), (1, 2, -3), (1, 2, 3)]
This will feed all the pairs as separate arguments to product
, which will then give you the cartesian product of them.
The reason your version isn’t working is that you are giving product
only one argument. Asking for a cartesian product of one list is a trivial case, and returns a list containing only one element (the list given as argument).