'Return the values of the dice like (3x2[+2x1])+1.'

def get_compressed_string(self):

    dice = self.dice.items()
    faces = ((u'%dx%d' % (times, face)) for (face, times) in dice)
    dice_str = u'+'.join(faces)
    dropped_str = u''
    if self.dropped:
        dropped = self.dropped.items()
        dfaces = ((u'%dx%d' % (times, face)) for (face, times) in dropped)
        dropped_str = (u'[+%s]' % (u'+'.join(dfaces),))
    plus_str = u''
    if self.addition:
        plus_str = u'{:+d}'.format(self.addition)
    return (u'(%s%s)%s' % (dice_str, dropped_str, plus_str))
