return (container_port, (ip, host_port)) or (container_port, host_port)

def pair(self):
        """return (container_port, (ip, host_port)) or (container_port, host_port)"""
        if self.ip is NotSpecified:
            if self.ip is NotSpecified:
                second = self.host_port
            else:
                second = (self.ip, )
        else:
            second = (self.ip, self.host_port)
        return self.container_port.port_str, second