'Checks that at most one type of scaling is enabled.'

def CheckScalingConstraints(self):

    scaling_num = sum([(x is not None) for x in [self.app_engine_web_xml.basic_scaling, self.app_engine_web_xml.automatic_scaling, self.app_engine_web_xml.manual_scaling]])
    if (scaling_num > 1):
        self.errors.append('Cannot    enable    more    than    one    type    of    scaling')
