Convert an IP string to a number and vice versa

converting an IP string to long integer:

import socket, struct

def ip2long(ip):
    """
    Convert an IP string to long
    """
    packedIP = socket.inet_aton(ip)
    return struct.unpack("!L", packedIP)[0]

the other way around:

>>> socket.inet_ntoa(struct.pack('!L', 2130706433))
'127.0.0.1'

Here's a summary of all options as of 2017-06. All modules are either part of the standard library or can be installed via pip install.

ipaddress module

Module ipaddress (doc) is part of the standard library since v3.3 but it's also available as an external module for python v2.6,v2.7.

>>> import ipaddress
>>> int(ipaddress.ip_address('1.2.3.4'))
16909060
>>> str(ipaddress.ip_address(16909060))
'1.2.3.4'
>>> int(ipaddress.ip_address(u'1000:2000:3000:4000:5000:6000:7000:8000'))
21268296984521553528558659310639415296L
>>> str(ipaddress.ip_address(21268296984521553528558659310639415296L))
u'1000:2000:3000:4000:5000:6000:7000:8000'

No module import (IPv4 only)

Nothing to import but works only for IPv4 and the code is longer than any other option.

>>> ipstr = '1.2.3.4'
>>> parts = ipstr.split('.')
>>> (int(parts[0]) << 24) + (int(parts[1]) << 16) + \
          (int(parts[2]) << 8) + int(parts[3])
16909060
>>> ipint = 16909060
>>> '.'.join([str(ipint >> (i << 3) & 0xFF)
          for i in range(4)[::-1]])
'1.2.3.4'

Module netaddr

netaddr is an external module but is very stable and available since Python 2.5 (doc)

>>> import netaddr
>>> int(netaddr.IPAddress('1.2.3.4'))
16909060
>>> str(netaddr.IPAddress(16909060))
'1.2.3.4'
>>> int(netaddr.IPAddress(u'1000:2000:3000:4000:5000:6000:7000:8000'))
21268296984521553528558659310639415296L
>>> str(netaddr.IPAddress(21268296984521553528558659310639415296L))
'1000:2000:3000:4000:5000:6000:7000:8000'

Modules socket and struct (ipv4 only)

Both modules are part of the standard library, the code is short, a bit cryptic and IPv4 only.

>>> import socket, struct
>>> ipstr = '1.2.3.4'
>>> struct.unpack("!L", socket.inet_aton(ipstr))[0]
16909060
>>> ipint=16909060
>>> socket.inet_ntoa(struct.pack('!L', ipint))
'1.2.3.4'