Determine if a Sudoku is valid, according to: Sudoku Puzzles  The Rules. The Sudoku board could be partially filled, where empty cells are filled with the character '.'.
def is_valid_sudoku(self, board):
    seen = []
    for i, row in enumerate(board):
        for j, c in enumerate(row):
            if c != '.':
                seen += [(c,j),(i,c),(i/3,j/3,c)]
    return len(seen) == len(set(seen))
