Why a[0][0]==a[1][0] ?

Question

I thought the output would be [[2,3], [3,3]].
But it seems that a[0][0]==a[1][0].
https://code.sololearn.com/cMk9E0Oh0LJ4/?ref=app

Answer 1

The way you created the list, a[0] is indeed a[1]

try
print(a[0] is a[1])
and you will get True.

you should do
a = [[2,3] for _ in range(2)]

Answer 2

When you duplicate reference types, you copy references. Both members of your array reference the same array. If you change the one, you change the other.

Answer 3

The only thing I can think of here is that when you do the multiplication in the first line, it creates a second item in the outer list that points to wherever the item that was already there (in this case, the inner list) is stored, instead of creating another unique instance of it. In this way, when you change one, you inherently change the other, because they point to the same space in memory.