Solved by ptrblck in post #2 
              
              
                Negative dimensions start from the end, so -1 would be the last dimension, -2 the one before etc.: 
        [1, 256, 7, 7]
pos dim: 0,   1,  2, 3
neg dim: -4, -3, -2, -1

If you are passing dimensions outside of this range, you should get an error: 
IndexError: Dimension out of range (expected to be…