How to solve diagonally constraint sudoku? - python-3.x

Question

Write a program to solve a Sudoku puzzle by filling the empty cells where 0 represent empty cell.
Rules:
All the number in sudoku must appear exactly once in diagonal running from top-left to bottom-right.
All the number in sudoku must appear exactly
once in diagonal running from top-right to bottom-left.
All the number in sudoku
must appear exactly once in a 3*3 sub-grid.
However number can repeat in row or column.
Constraints:
N = 9; where N represent rows and column of grid.
What I have tried:
N = 9
def printing(arr):
for i in range(N):
for j in range(N):
print(arr[i][j], end=" ")
print()
def isSafe(grid, row, col, num):
for x in range(9):
if grid[x][x] == num:
return False
cl = 0
for y in range(8, -1, -1):
if grid[cl][y] == num:
cl += 1
return False
startRow = row - row % 3
startCol = col - col % 3
for i in range(3):
for j in range(3):
if grid[i + startRow][j + startCol] == num:
return False
return True
def solveSudoku(grid, row, col):
if (row == N - 1 and col == N):
return True
if col == N:
row += 1
col = 0
if grid[row][col] > 0:
return solveSudoku(grid, row, col + 1)
for num in range(1, N + 1, 1):
if isSafe(grid, row, col, num):
grid[row][col] = num
print(grid)
if solveSudoku(grid, row, col + 1):
return True
grid[row][col] = 0
return False
if (solveSudoku(grid, 0, 0)):
printing(grid)
else:
print("Solution does not exist")
Input:
grid =
[
[0, 3, 7, 0, 4, 2, 0, 2, 0],
[5, 0, 6, 1, 0, 0, 0, 0, 7],
[0, 0, 2, 0, 0, 0, 5, 0, 0],
[2, 8, 3, 0, 0, 0, 0, 0, 0],
[0, 5, 0, 0, 7, 1, 2, 0, 7],
[0, 0, 0, 3, 0, 0, 0, 0, 3],
[7, 0, 0, 0, 0, 6, 0, 5, 0],
[0, 2, 3, 0, 3, 0, 7, 4, 2],
[0, 5, 0, 0, 8, 0, 0, 0, 0]
]
Output:
8 3 7 0 4 2 1 2 4
5 0 6 1 8 6 3 6 7
4 1 2 7 3 5 5 0 8
2 8 3 5 4 8 6 0 5
6 5 0 0 7 1 2 1 7
1 4 7 3 2 6 8 4 3
7 8 1 4 1 6 3 5 0
6 2 3 7 3 5 7 4 2
0 5 4 2 8 0 6 8 1
Basically I am stuck on the implementation of checking distinct number along diagonal. So question is how I can make sure that no elements gets repeated in those diagonal and sub-grid.