gvrocha - 2 months ago 12
Python Question

# How to apply itertools.product to elements of a list of lists?

I have a list of arrays and I would like to get the cartesian product of the elements in the arrays.

I will use an example to make this more concrete...

itertools.product seems to do the trick but I am stuck in a little detail.

``````arrays = [(-1,+1), (-2,+2), (-3,+3)];
``````

If I do

``````cp = list(itertools.product(arrays));
``````

I get

``````cp = cp0 = [((-1, 1),), ((-2, 2),), ((-3, 3),)]
``````

But what I want to get is

``````cp1 = [(-1,-2,-3), (-1,-2,+3), (-1,+2,-3), (-1,+2,+3), ..., (+1,+2,-3), (+1,+2,+3)].
``````

I have tried a few different things:

``````cp = list(itertools.product(itertools.islice(arrays, len(arrays))));
cp = list(itertools.product(iter(arrays, len(arrays))));
``````

They all gave me cp0 instead of cp1.

Any ideas?

``````>>> list(itertools.product(*arrays))
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).