Add element in a list in a list

Question

I have a list of list and I would like to add an element inside only one of the list but it is added everywhere. You can find my code bellow

repartition_labels = [[]]*3
repartition_labels[2].append(2)

The result I have is

[[2], [2], [2]]

and I would like to have the result

[[], [], [2]]

I already tried to function insert and extend but it didn't solve the problem

Use a list comprehension to construct the list. In this case it's only create 3 reference to the same list object. — Abdul Niyas P M, Nov 10 '20 at 10:49

score 2 · Answer 1 · answered Nov 10 '20 at 10:52

2

With repartition_labels = [[]]*3, you are generating a list which contains 3 references to the same object.

When you change that object, all references will show the (same) updated object.

answered Nov 10 '20 at 10:52

goodvibration

score 1 · Accepted Answer · answered Nov 10 '20 at 10:50

1

You have to do this:

repartition_labels = [[] for _ in range(0, 3)]
repartition_labels[2].append(2)

Output:

[[], [], [2]]

The reason your code is not working as expected, is because by [[]] * 3 you're creating three references to the same list.

answered Nov 10 '20 at 10:50

baduker

2 Answers2