Editing List of list of list in Python

Question

I am trying to edit elements in my list of list of list but it is editing multiple elements.

    L1 = [[0,0] for count in range(2)]
    L2 = [L1 for count in range(2)]
    L2[0][0][0] = 5
    print(L2)

What I expect is [[[5, 0], [0, 0]], [[0, 0], [0, 0]]]

But what I get is [[[5, 0], [0, 0]], [[5, 0], [0, 0]]]

It seems that I am editing the original list. Can someone explain how to edit a single element or set up nested lists where this effect won't occur.

Many thanks

Every element of L2 is the same list as L1: `all(a is L1 for a in L2)` is True. — Dan D., Nov 17 '16 at 21:01
in L2, it's a reference to lists made in L1. Python lists are mutable. — adarsh, Nov 17 '16 at 21:02

Alex Hall · Answer 1 · 2016-11-17T21:25:36.703

1

Don't reuse the variable:

L2 = [[[0,0] for count in range(2)] for count in range(2)]

Then the inner part [[0,0] for count in range(2)] will get recreated every time as a fresh, separate list.

edited Nov 17 '16 at 21:25

answered Nov 17 '16 at 21:03

Alex Hall

@MoinuddinQuadri The linked questions are generally about a list that has been multiplied, e.g. `[[0] * 2] * 2`. OP's case is ever so slightly different. – Alex Hall Nov 17 '16 at 21:13
@MoinuddinQuadri like that? – Alex Hall Nov 17 '16 at 21:25

1 Answers1