How do I replace elements in two-dimensional array in python?

My task is to replace all the elements whose both indexes are odd with 1, and all the elements whose both indexes are even with -1.

>Solution :

You can replace elements by using a double index like: array[y][x] if array is list of lists.

This is a example:

array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
length = len(array)
for y in range(length):
    for x in range(length):
        if y % 2 and x % 2:
            array[y][x] = 1
        elif y % 2 == 0 and x % 2 == 0:
            array[y][x] = 0
print(array)

This will output: [[0, 2, 0], [4, 1, 6], [0, 8, 0]]