code: def attach_subnets(self, subnets):
          
          if isinstance(subnets, str) or isinstance(subnets, unicode):
              subnets = [subnets]
          new_subnets = self.connection.attach_lb_to_subnets(self.name, subnets)
          self.subnets = new_subnets
docs: Attaches load balancer to one or more subnets.
          Attaching subnets that are already registered with the 
          Load Balancer has no effect.
  
          :type subnets: string or List of strings
          :param subnets: The name of the subnet(s) to add.