python - socket.error: port/proto not found -

i'm trying service name of port number 1521 using socket package. code i'm trying execute in shell

import socket portname = socket.getservbyport(1521) print portname 

the error i'm getting below

portname = socket.getservbyport(i) socket.error: port/proto not found 

if i'm using other port such 22,80,1433,3306 isn't problem in retrieving port/service name. i've tried similar code on 2 other linux machine isn't response.