sudoku.py

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

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)):
			if bo[i][j]==0:
				return (i,j)	#row,col
	return None

print_board(board)
solve(board)
print(" ")
print("=====================")
print("======Solution=======")
print("=====================")
print(" ")
print_board(board)