Python list multiply and index

Question

I create 3 empty list nested in a list, and index to append to the first one, but it results in all the list:

In [1]:
   ...: a = [[]] * 3
   ...: a[0].append(3)
   ...: print(a)

Out [1]:
[[3], [3], [3]]

My expect output is:

[[3], [], []]

But if I do this:

In [2]:
   ...: b = []
   ...: for i in range(3):
   ...: b.append([])
   ...: b[0].append(3)
   ...: print(b)

Out [2]:
    [[3], [], []]

Then I got my expect output

Thanks

Please format your code. Did you have a question? – jarmod Oct 22 '21 at 00:37 — jarmod, Oct 22 '21 at 00:37

Mostafa Wael · Accepted Answer · 2021-10-22T00:52:03.340

2

Because in the first case, you are trying to access the same object (the object and its refernces).

But in the second case, list a has totally different -new- objects.

edited Oct 22 '21 at 00:52

answered Oct 22 '21 at 00:43

Mostafa Wael

If this answer helped you, please select it as the right answer :-) – Mostafa Wael Oct 22 '21 at 00:51

1 Answers1