While loop incorrectly updating the variables [duplicate]

Question

I have a while loop in my python code which contains a nested for loop that loops over a 2D array. The variable T needs to get updated at end of the while loop. However I'm seeing that the variable is getting updated within the for loop itself. What am I doing incorrectly here and how to modify this?

error = 1
tolerance = 1e-6
T = T_new
itr = 0
while error>tolerance:
    itr = itr+1
    for i in range(1,imax-1):
        for j in range(1,jmax-1):
            T_new[i,j]=0.25*(T[i-1,j]+T[i+1,j]+T[i,j-1]+T[i,j+1])
    error = np.max(np.abs(T_new-T))
    T = T_new

Answer 1

In python, only primitives: ints, floats, strings, are copied by value. Lists, dicts, and objects by default are copied by reference.

You can from copy import deepcopy and use T = deepcopy(T_new) to get the behavior you want. Before doing so though, think about if you are writing your code in an optimal manner. For example, you use itr = itr + 1 instead of itr += 1. Also think about formatting. Use an auto formatter if you can't bother to write your code properly.