What is the difference between [[]]*4 and [[],[],[],[]]

Question

I create two lists that seems the same

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

since when I print x, y, they give me the same output [[],[],[],[]]. However, when I apply the same operation x[0].append((1,2)), y[0].append((1,2)) on them, they give me different result

print x  >> [[(1, 2)], [(1, 2)], [(1, 2)], [(1, 2)]]
print y  >> [[(1, 2)], [], [], []]

Why this happens? And how to modify x to make sure x and y are exactly the same?

Short answer: [[]] creates 4 references to the same list. See Michael0x2a's link for a longer answer. — Dyrborg, Aug 03 '15 at 15:46
Also see [here](https://stackoverflow.com/questions/2612802/how-to-clone-or-copy-a-list-in-python) — Cory Kramer, Aug 03 '15 at 15:47

score 3 · Accepted Answer · answered Aug 03 '15 at 15:46

3

x is a list that references 4 times the same list.

y is a list of 4 independent empty lists.

answered Aug 03 '15 at 15:46

hiro protagonist

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What is the difference between [[]]*4 and [[],[],[],[]]

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