'The ModifyCacheSubnetGroup operation modifies an existing
cache subnet group.
:type cache_subnet_group_name: string
:param cache_subnet_group_name: The name for the cache subnet group.
This value is stored as a lowercase string.
Constraints: Must contain no more than 255 alphanumeric characters or
hyphens.
Example: `mysubnetgroup`
:type cache_subnet_group_description: string
:param cache_subnet_group_description: A description for the cache
subnet group.
:type subnet_ids: list
:param subnet_ids: The EC2 subnet IDs for the cache subnet group.'

def modify_cache_subnet_group(self, cache_subnet_group_name, cache_subnet_group_description=None, subnet_ids=None):

    params = {'CacheSubnetGroupName': cache_subnet_group_name}
    if (cache_subnet_group_description is not None):
        params['CacheSubnetGroupDescription'] = cache_subnet_group_description
    if (subnet_ids is not None):
        self.build_list_params(params, subnet_ids, 'SubnetIds.member')
    return self._make_request(action='ModifyCacheSubnetGroup', verb='POST', path='/', params=params)
