Python 多级排序

class C( object ):        def __init__( self, x1, x2, x3 ):        self.x1 = x1        self.x2 = x2        self.x3 = x3    def __cmp__( self, other ):        if self.x1 < other.x1:            return -1        elif self.x1 == other.x1:            if self.x2 < other.x2:                return -1            elif self.x2 == other.x2:                if self.x3 < other.x3:                    return -1                elif self.x3 == other.x3:                    return 0                else:                    return 1            else:                return 1        else:            return 1    def __repr__( self ):        return "({x1}, {x2}, {x3})".format( x1 = self.x1,                                            x2 = self.x2,                                            x3 = self.x3 )        import randomr = random.randintli = []for i in xrange( 15 ):    li.append( C( r( 1, 10 ), r( 1, 10 ), r( 1, 10 ) ) )for i in li:    print iprint li1 = sorted( li )for i in li1:    print i