Can't modify a simple matrix

[deanhystad]

I don't think this does what you think.

SiteVierge2d=[[0]*(8)]*(5)

To start with, the parenthesis have no effect here. The code runs the same with or without.

More importnatly, SiteVierge2d[0] is the same list as SiteVierge2d[1] and SiteVierge2d[2]... You can see that if you look at the object ID's. All 5 lists in SiteVierge2d are the same object.

SiteVierge2d=[[0]*(8)]*(5)
print(*map(id, SiteVierge2d))

Output:
1776206706304 1776206706304 1776206706304 1776206706304 1776206706304

It is the same as if you wrote this:

zeros = [0] * 8
SiteVierge2d = [zeros] * 5

I think you want to do something like this:

SiteVierge2d = [[0]*8 for _ in range(5)]
print(*map(id, SiteVierge2d))

2218135596032 2218135268288 2218135123136 2218135124096 2218135599936

Now each of the lists in SiteVierge2d are different lists because [0] * 8 was executed 5 times.

I don't think this does what you think either:

M=S[:]

This does not make a deep copy. The lists in M are the same lists in S. If you set M[1][2] = 3 then S[1][2] == 3. If you want M to be a new 2D array with the same values as S, you need to do a deep copy.

https://docs.python.org/3/library/copy.html