:return: Swiss UID number

def vat_id(self):
        """
        :return: Swiss UID number
        """
        def _checksum(digits):
            code = ['8', '6', '4', '2', '3', '5', '9', '7']
            remainder = 11-(sum(map(lambda x, y: int(x) * int(y), code, digits)) % 11)
            if remainder == 10:
                return 0
            elif remainder == 11:
                return 5
            return remainder

        vat_id = self.bothify('########')
        return 'CHE' + vat_id + str(_checksum(vat_id))