The following code surprised me.
alist = [[]] * 4
alist[0].append(100)
I expected that alist would be
[[100],[],[],[]]
but it turned out to be
[[100],[100],[100],[100]]
Does anyone know why python works that way? thank you.
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That's the difference of value and reference.list is same as reference. – stars seven Mar 02 '20 at 18:52
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You could check that is the same reference with help of `is` such that `alist[0] is alist[1]` is True but in other case `alist = [[] for _ in range(4)]` all references will be points to a 4 different empty list objects. Also check that `alist[0] is []` is False. – frost-nzcr4 Mar 02 '20 at 21:05
2 Answers
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on this line alist = [[]] * 4 you are creating one inner list and 4 references to the same list, to fix this you can use:
alist = [[] for _ in range(4)]
kederrac
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alist1 = [[] for _ in range(4)]
alist1[0] = 100
print(alist1)
vijju
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After the first line you can just `alist1[0] = 100`. No need for the second loop – Ghasem Mar 03 '20 at 07:26
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