Crappy python solver for a Set game (e.g., http://www.nytimes.com/ref/crosswords/setpuzzle.html/ )

solver.py

class Colour:
    red    = 'r'
    green  = 'g'
    purple = 'p'

class Style:
    solid   = 'sl'
    striped = 'st'
    open    = 'o'

class Shape:
    squiggly  = 's'
    diamond   = 'd'
    ellipse   = 'e'

class Card:
    __colours = ('r', 'g', 'p')
    __styles  = ('sl', 'st', 'o')
    __shapes  = ('s', 'd', 'e')
    __numbers = (1, 2, 3)

    def __init__(self, colour, style, shape, number):
        assert(colour in Card.__colours)
        assert(style  in Card.__styles)
        assert(number in Card.__numbers)
        assert(shape  in Card.__shapes)

        self.style  = style
        self.shape  = shape
        self.number = number
        self.colour = colour

    def get_final_card(self, other):
        style  = ""
        shape  = ""
        number = ""
        colour = ""

        if other.colour == self.colour:
            colour = self.colour
        else:
            colour = [i for i in Card.__colours if i not in (self.colour, other.colour)][0]

        if other.style == self.style:
            style = self.style
        else:
            style = [i for i in Card.__styles if i not in (self.style, other.style)][0]

        if other.number == self.number:
            number = self.number
        else:
            number = [i for i in Card.__numbers if i not in (self.number, other.number)][0]

        if other.shape == self.shape:
            shape = self.shape
        else:
            shape = [i for i in Card.__shapes if i not in (self.shape, other.shape)][0]

        return Card(colour, style, shape, number)

    def __eq__(self, other):
        return self.colour == other.colour and self.style == other.style and \
               self.number == other.number and self.shape == other.shape

    def __lt__(self, other):
        if self.number != other.number:
            return self.number < other.number

        if self.colour != other.colour:
            return self.colour < other.colour

        if self.style != other.style:
            return self.style < other.style

        if self.shape != other.shape:
            return self.style < other.shape

        return False

    def __repr__(self):
        return "Card('%s', '%s', '%s', %d)" % (self.colour, self.style, self.shape, self.number)


def solve(cards):
    solutions = []

    for idx, c in enumerate(cards[:-1]):
        for c2 in cards[idx + 1:]:
            tmp = c.get_final_card(c2)

            if tmp in cards:
                solution = [c, c2, tmp]
                solution.sort()

                if solution not in solutions:
                    solutions.append(solution)

    return solutions