find usage for elasticache parameter groups

def _find_usage_parameter_groups(self):
        """find usage for elasticache parameter groups"""
        num_groups = 0

        paginator = self.conn.get_paginator('describe_cache_parameter_groups')
        for page in paginator.paginate():
            for group in page['CacheParameterGroups']:
                num_groups += 1
        self.limits['Parameter Groups']._add_current_usage(
            num_groups,
            aws_type='AWS::ElastiCache::ParameterGroup'
        )