def print_diagonals(list2d):
size = len(list2d)
primary = [list2d[i][i] for i in range(size)]
print(primary)
secondary = [list2d[i][size - 1 - i] for i in range(size)]
print(secondary)
list2d = [[ 1, -1, 77],
[-2, 88, -3],
[99, -4, 3]]
print_diagonals(list2d)
'''
run:
[1, 88, 3]
[77, 88, 99]
'''