Sudoku Solver

def find_empty_cell(board):
    for board_row in range(9):
        for board_cow in range(9):
            if board[board_row][board_cow] == '':
                return board_row, board_cow

    return None, None


def is_valid(board, prediction, row, col):
    row_vals = board[row]
    if prediction in row_vals:
        return False

    col_vals = [board[i][col] for i in range(9)]
    if prediction in col_vals:
        return False

    row_start = (row // 3) * 3
    col_start = (col // 3) * 3

    for r in range(row_start, row_start + 3):
        for c in range(col_start, col_start + 3):
            if board[r][c] == prediction:
                return False

    return True


def solver(board):
    row, col = find_empty_cell(board)

    if row is None:
        return True

    for guess in range(1, 10):
        if is_valid(board, guess, row, col):
            board[row][col] = guess
            if solver(board):
                return True
        board[row][col] = ''

    return False


matrix = [
    ['6', '3', '', '', '', '', '', '8', '1'],
    ['', '2', '', '', '', '3', '', '', ''],
    ['', '', '', '', '1', '7', '4', '3', ''],

    ['', '9', '6', '4', '', '', '5', '7', ''],
    ['', '', '', '7', '6', '2', '', '', ''],
    ['', '8', '', '', '', '', '6', '', ''],

    ['', '6', '', '', '2', '', '', '', ''],
    ['3', '', '9', '', '', '', '', '6', ''],
    ['', '', '', '', '', '', '', '', '9']
]
print(solver(matrix))
for j in matrix:
    print(', '.join(map(str, j)))


# matrix = [
#     ['', '', '', '', '', '', '', '', ''],
#     ['', '', '', '', '', '', '', '', ''],
#     ['', '', '', '', '', '', '', '', ''],
#
#     ['', '', '', '', '', '', '', '', ''],
#     ['', '', '', '', '', '', '', '', ''],
#     ['', '', '', '', '', '', '', '', ''],
#
#     ['', '', '', '', '', '', '', '', ''],
#     ['', '', '', '', '', '', '', '', ''],
#     ['', '', '', '', '', '', '', '', '']
# ]