2d Array adds last element to entire list

[bowlofred]

Your initial problem was that you were not making different lists, but just several copies of one list. The construction: [[]] * num takes the inside list and makes num references to it, but they're all the same list. So each time through was overwriting the previous trips through the loop.

>>> players = [[0] * 4] * 3
>>> players
[[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
>>> players[0][1] = "x"
>>> players
[[0, 'x', 0, 0], [0, 'x', 0, 0], [0, 'x', 0, 0]]

For this to work, you'd need to make different lists.

>>> players = [[0] * 4 for x in range(3)]
>>> players
[[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
>>> players[0][1] = "x"
>>> players
[[0, 'x', 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]