Hacker rank Diagonal Difference

#!/bin/python3
 
import math
import os
import random
import re
import sys
 
#
# Complete the 'diagonalDifference' function below.
#
# The function is expected to return an INTEGER.
# The function accepts 2D_INTEGER_ARRAY arr as parameter.
#
 
def diagonalDifference(arr):
    # Write your code here
    cnt=len(arr)
    primary=0
    secondary=0
    for i in range(cnt):
        primary+=arr[i][i]
        secondary+=arr[cnt-i-1][i]
    return abs(primary-secondary)
if __name__ == '__main__':
    fptr = open(os.environ['OUTPUT_PATH'], 'w')
 
    n = int(input().strip())
 
    arr = []
 
    for _ in range(n):
        arr.append(list(map(int, input().rstrip().split())))
 
    result = diagonalDifference(arr)
 
    fptr.write(str(result) + '\n')
 
    fptr.close()