[guest@localhost ~]$ awk '$2 ~ /^(21|80|110|139|1080)\/tcp/' /etc/services
ftp             21/tcp
http            80/tcp          www www-http    # WorldWideWeb HTTP
pop3            110/tcp         pop-3           # POP version 3
netbios-ssn     139/tcp                         # NETBIOS session service
socks           1080/tcp                        # socks proxy server
[guest@localhost ~]$

  
>>> port_names = {
...     21: 'ftp',
...     80: 'http',
...     110: 'pop3'
... }
>>> 
>>> print(21, '->', port_names[21])
21 -> ftp
>>>