code: def get_all_subnets(self, subnet_ids=None, filters=None):
          
          params = {}
          if subnet_ids:
              self.build_list_params(params, subnet_ids, 'SubnetId')
          if filters:
              i = 1
              for filter in filters:
                  params[('Filter.%d.Name' % i)] = filter[0]
                  params[('Filter.%d.Value.1' % i)] = filter[1]
                  i += 1
          return self.get_list('DescribeSubnets', params, [('item', Subnet)])
docs: Retrieve information about your Subnets.  You can filter results to
          return information only about those Subnets that match your search
          parameters.  Otherwise, all Subnets associated with your account
          are returned.
  
          :type subnet_ids: list
          :param subnet_ids: A list of strings with the desired Subnet ID's
  
          :type filters: list of tuples
          :param filters: A list of tuples containing filters.  Each tuple
                          consists of a filter key and a filter value.
                          Possible filter keys are:
  
                          - *state*, the state of the Subnet
                            (pending,available)
                          - *vpdId*, the ID of teh VPC the subnet is in.
                          - *cidrBlock*, CIDR block of the subnet
                          - *availabilityZone*, the Availability Zone
                            the subnet is in.
  
  
          :rtype: list
          :return: A list of :class:`boto.vpc.subnet.Subnet`