Python assignment of values within an array

Question

I am trying to copy a vector several times and then change one of its elements:

from copy import deepcopy

v = [0.5,1.0,2.0]
m = 3 * [deepcopy(v)]
# m = [[0.5,1.0,2.0],[0.5,1.0,2.0],[0.5,1.0,2.0]]
m [0][0] = "Python"
# m = [["Python",1.0,2.0],["Python",1.0,2.0],["Python",1.0,2.0]]

as you can see instead of just changing the 0 element form the 0 array, it is changing all the 0 elements. What am I doing wrong?

Thanks!

Your code seems to be correct, except for the last line. The last line is output or part of the code? — Shadab Hussain, Mar 15 '20 at 14:52
Does this answer your question? [List of lists changes reflected across sublists unexpectedly](https://stackoverflow.com/questions/240178/list-of-lists-changes-reflected-across-sublists-unexpectedly) — Tomerikoo, Mar 15 '20 at 14:57

Kenta Nomoto · Accepted Answer · 2020-03-15T15:13:24.453

4

What you did here was that you made three references to the same thing.

3 * [deepcopy(v)] simply made 3 different references to the same list.

You would want to do

m = [deepcopy(v) for x in range(3)]

edited Mar 15 '20 at 15:13

answered Mar 15 '20 at 14:52

Kenta Nomoto

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Python assignment of values within an array

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