Just figured why: If I type this on the kernel: weirdList = [[0]*3]*5 weirdList Out[257]: [[0, 0, 0], [0, 0, 0], [0, 0, 0], [0, 0, 0], [0, 0, 0]] weirdList[0][0] = 1 weirdList Out[259]: [[1, 0, 0], [1, 0, 0], [1, 0, 0], [1, 0, 0], [1, 0, 0]] All first elements of the sublists also changes. I dunno why...