Variable Updating (Python)

I am trying to create a 3D cube matrix and here is the matrix:

cube = [
    [
        ['W', 'W', 'W'],
        ['W', 'W', 'W'],
        ['W', 'W', 'W']
    ],   
    [
        ['G', 'G', 'G'],
        ['G', 'G', 'G'],
        ['G', 'G', 'G']
    ],
    [
        ['R', 'R', 'R'],
        ['R', 'R', 'R'],
        ['R', 'R', 'R']
    ],
    [
        ['B', 'B', 'B'],
        ['B', 'B', 'B'],
        ['B', 'B', 'B']
    ],
    [
        ['O', 'O', 'O'],
        ['O', 'O', 'O'],
        ['O', 'O', 'O']
    ],
    [
        ['Y', 'Y', 'Y'],
        ['Y', 'Y', 'Y'],
        ['Y', 'Y', 'Y']
    ],
]

I also have a function with the rotations:

def cube_rotation(rotation):
    if 'U' in rotation:
        cube_g = cube[1]
        direction = 1
        if '\'' in rotation: direction = -1;
        for i in range(1,4):
            cube[i][0] = cube[i+direction][0];
        cube[4][0] = cube_g[0];
    print(cube)
cube_rotation('U')

The U rotation basically means to turn the top of the cube to left. [![[![enter image description here][1]][1] [1]: https://i.sstatic.net/XYqVm.png

What I expect as the outcome is:

[
[['W', 'W', 'W'], ['W', 'W', 'W'], ['W', 'W', 'W']], 
[['R', 'R', 'R'], ['G', 'G', 'G'], ['G', 'G', 'G']], 
[['B', 'B', 'B'], ['R', 'R', 'R'], ['R', 'R', 'R']], 
[['O', 'O', 'O'], ['B', 'B', 'B'], ['B', 'B', 'B']], 
[['G', 'G', 'G'], ['O', 'O', 'O'], ['O', 'O', 'O']], # Point of Conflict (4th index)
[['Y', 'Y', 'Y'], ['Y', 'Y', 'Y'], ['Y', 'Y', 'Y']]
]

but my actual outcome changes the 4th index to:

[['R', 'R', 'R'], ['O', 'O', 'O'], ['O', 'O', 'O']]

I probably assume this to be because cube_g is updating in the for loop but I don't find a reason why. It is before the for loop. I even tried changing the variable names and adding new variables to avoid any inconsiderable reasons, but nothing seems to work! Any ideas as to why this might happen?

You're referencing the original cube when assigning it to cube_g, you have to make a copy with .copy()

This should work:

def cube_rotation(rotation):
    if 'U' in rotation:
        cube_g = cube[1].copy()
        direction = 1
        if '\'' in rotation: direction = -1;
        for i in range(1,4):
            cube[i][0] = cube[i+direction][0];
        cube[4][0] = cube_g[0];
    print(cube)
cube_rotation('U')