See difference in output by changing array definition.

Please provide the output you see and the output you expect.

And it would be better if you could just post the code into the comment window. I, for one, cannot run your .ipynb file.

after = [[1,2],[3,4]]
rows, cols = (len(after), len(after[0])) 

before = [[0]*cols]*rows

# before = [[0 for i in range(cols)] for j in range(rows)]  #uncomment this array definition and comment above one... see difference in output.

print(before)

def calculation(a,b):
    s = after[0][0]
    for x in range(a+1):
        for y in range(b+1):
                s += before[x][y]
    before[a][b] = after[a][b] - s
    
def cal2():
    for x in range(len(after)):
        for y in range(len(after[0])):
            calculation(x,y)
    before[0][0] = after[0][0]
    print(before)
cal2()


#expected output: [[1, 1], [2, 0]]

Your example is too complex to work through in my head, but I suspect this is the issue you're seeing: https://docs.python.org/3/faq/programming.html#why-did-changing-list-y-also-change-list-x

In any event, this is almost certainly not a bug in Python, but rather in your code. You might want to ask this question on the python-list mailing list https://mail.python.org/mailman/listinfo/python-list or on Stack Overflow, which are more appropriate venues than the bug tracker.

See https://docs.python.org/3/faq/programming.html#how-do-i-create-a-multidimensional-list.

Thanks, Serhiy. That's a better section than I found.

I'm going to close this. @jeetshahj12375: If you can show that this is a bug in python, please re-open this issue.