Behaviour of 2D array

[buran]

The problem is how you create it on this line

torus = [[0] * MAXHORZ] * MAXVERT

lists are mutable and you populate with same object, thus when you update one, it is reflected elsewhere

rows = 3
cols = 4

spam = [[0] * cols] * rows
print(spam)
print([id(row) for row in spam])
spam[0][0] = 1
print(spam)
print('-----------------------')
eggs = [[0] * cols for _ in range(rows)]
print(eggs)
print([id(row) for row in eggs])
eggs[0][0] = 1
print(eggs)

Output:
[[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
[12470912, 12470912, 12470912]
[[1, 0, 0, 0], [1, 0, 0, 0], [1, 0, 0, 0]]
-----------------------
[[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
[13534272, 13534312, 13534152]
[[1, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]