Array initialization anomaly

[deanhystad]

x=[[0]*4]*10 creates the array[0, 0, 0, 0] and then makes an array that holds ten of these arrays. All of the arrays inside x are the same array. Not the same values (which they are), but the same array. It is as if you did this:

y=[0]*4
x=[y,y,y,y,y,y,y,y,y,y]

A slightly shorter version of what you came up with:

x=[[0]*4 for _ in range(10)]
x[0][0] = 1
print(x)

Output:
[[1, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], ...