Print Not Matching With An Array I'm Appending To

Question

I'm trying to make a function that takes an array of numbers and gives you every combination those numbers can be in, in two arrays.

My problem is that I can print the exact results that I want, but when I try to save the results into a variable, for some reason, I get the same sub-array spammed in my array.

Here is the code:

test = []
def partitioner(array1, array2):
    a = array1
    b = array2
    for _ in range(len(b)):
        a.append(b[0])
        del b[0]

        if(len(b) >= 1 and len(a) >= 1):
            print([a, b])       # This part right here, I'm printing the expected
            test.append([a, b]) # But this array is getting the actual
        partitioner(a, b)
        b.append(a[-1])
        del a[-1]

partitioner([], [x for x in range(3)])
print(test)

Expected:

[
[[0], [1, 2]],
[[0, 1], [2]],
[[0, 2], [1]],
[[1], [2, 0]],
[[1, 2], [0]],
[[1, 0], [2]],
[[2], [0, 1]],
[[2, 0], [1]],
[[2, 1], [0]]]

Actual:

[
[[], [0, 1, 2]],
[[], [0, 1, 2]],
[[], [0, 1, 2]], 
[[], [0, 1, 2]], 
[[], [0, 1, 2]], 
[[], [0, 1, 2]], 
[[], [0, 1, 2]], 
[[], [0, 1, 2]], 
[[], [0, 1, 2]]]

Answer 1

a and b are lists, so when they are overridden every iteration of the recursion with the last value it changes the values in test as well. Append a copy of a and b instead

test.append([a[:], b[:]])