working.py

board = [
    [7,8,0,4,0,0,1,2,0],
    [6,0,0,0,7,5,0,0,9],
    [0,0,0,6,0,1,0,7,8],
    [0,0,7,0,4,0,2,6,0],
    [0,0,1,0,5,0,9,3,0],
    [9,0,4,0,6,0,0,0,5],
    [0,7,0,3,0,0,0,1,2],
    [1,2,0,0,0,7,4,0,0],
    [0,4,9,2,0,6,0,0,7]
]

def solve(bo):
    find = find_empty(bo)
    if not find:
        return True
    else:
        row , col = find
    for i in range (1,10):
        if valid(bo, i, (row,col)):
            bo[row][col] = i

            if solve(bo):
                return True
            bo[row][col] = 0

    return False







def valid(bo,num,pos):
    #check row
    for i in range(len(bo[0])):
        if bo[pos[0]][i] == num and pos[1] != i:
            return False

    #check column
    for i in range(len(bo)):
        if bo[i][pos[1]] == num and pos[0] != i:
            return False

    #check box
    box_x = pos[1] // 3
    box_y = pos[0] // 3

    for i in range(box_y*3 , box_y*3 + 3):
        for j in range(box_x *3 , box_x*3 + 3):
            if bo[i][j] == num and (i,j) != pos:
                return False

    return True


def print_board(bo):
    for i in range(len(bo)):
        if i % 3== 0 and i!=0:
            print("- - - - - - - - - - - ")

        for j in range(len(bo[0])):
            if j%3==0 and j!=0:
                print(" | ", end="")

            if j==8:
                print(bo[i][j])
            else:
                print(str(bo[i][j]) + " ", end="")

def find_empty(bo):
    for i in range(len(bo)):
        for j in range(len(bo[0])):
            if bo[i][j] == 0:
                return (i,j) # row,col
    return None

print_board(board)
solve(board)
print("----------------------\n----------------------")
print_board(board)