How to solve diagonally constrained sudoku.

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 left-top to right-bottom diagonal.
All the number in sudoku must appear exactly once in right-top to left-bottom diagonal.
All the number in sudoku must appear exactly once in a square(3*3).
However number can repeat in row or column.

Basically I am stuck on the implementation of checking distinct number along diagonal. So my question is how I can make sure that no elements gets repeated in those diagonal and sub-grid.

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