Simple 15puzzle repr

#usr/bin/env python

from sys import argv


class DimensionMismatchException(BaseException):
    pass

class Blank(object):
    def __repr__(self):
        return 'B'


class Puzzle:
    rows = 0
    cols = 0
    array = None
    blank = None

    def __init__(self, rows, cols, *data):
        if len(data) != rows*cols - 1:
            raise DimensionMismatchException('not enough data')

        self.rows = rows
        self.cols = cols
        self.array = list(data)
        self.blank = Blank()
        self.array.append(self.blank)

    def __repr__(self):
        puzzle = ''

        for i in range(self.rows):
            if i > 0:
                puzzle = puzzle + '\n'

            puzzle = puzzle + str(self.array[i*self.rows:i*self.rows + self.cols])

        return puzzle

    def up(self):
        pos = self.array.index(self.blank)
        if pos < self.cols:
            return
        else:
            upper = pos - self.cols
            d = self.array[upper]
            self.array[pos] = d
            self.array[upper] = self.blank

    def down(self):
        pos = self.array.index(self.blank)
        if pos >= (self.rows - 1) * self.cols:
            return
        else:
            downer = pos + self.cols
            d = self.array[downer]
            self.array[pos] = d
            self.array[downer] = self.blank

    def right(self):
        pos = self.array.index(self.blank)
        if (pos + 1) % self.cols == 0:
            return
        else:
            righty = pos + 1
            d = self.array[righty]
            self.array[pos] = d
            self.array[righty] = self.blank

    def left(self):
        pos = self.array.index(self.blank)
        if pos % self.cols == 0:
            return
        else:
            lefty = pos - 1
            d = self.array[lefty]
            self.array[pos] = d
            self.array[lefty] = self.blank

if __name__ == '__main__':
    rows = int(argv[1])
    cols = int(argv[2])

    data = [int(i) for i in  argv[3:]]

    puzzle = Puzzle(rows, cols, *data)
    print('tablero en posicion 0:')
    print(puzzle)
    puzzle.up()
    print('un movimiento hacia arriba:')
    print(puzzle)
    puzzle.left()
    print('y ahora hacia la izquierda')
    print(puzzle)