finding IP addresses of all local adapters in Python

We've got an XmlRpcServer app written in Python, and when we wanted it to run on several different servers I thought I was being clever and rather than hardcode the IP address I'd just look it up; a quick search on the intertubes turned suggested:

serverIP= socket.gethostbyname(socket.gethostname())


This worked great on the original workstation we'd been running the script from, but when I put it on another machine it failed. Turns out, that machine has two network adapters, and you need to call the gethostbyname_ex() version (which the python docs don't have much to say about). That version of the call returns a list with all the adapters, and you need to search through them for the one you want. this is how I did it:


Python 2.5.2 (r252:60911, Dec 2 2008, 09:26:14)
[GCC 3.4.4 (cygming special, gdc 0.12, using dmd 0.125)] on cygwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import socket
>>> socket.gethostbyname(socket.gethostname())
'192.168.20.200'
>>> socket.gethostbyaddr(socket.gethostname())
('bigServer', [], ['192.168.20.200'])
>>> socket.gethostbyname_ex(socket.gethostname())
('bigServer.mydomain.com', [], ['192.168.20.200', '192.168.1.41'])
>>>
>>> def getIpAddrForSubnet(subnetStr):
... ipAddrs= socket.gethostbyname_ex(socket.gethostname())
... for value in ipAddrs[2]:
... if str(value).find(subnetStr) >= 0: return value
...
>>> getIpAddrForSubnet("192.168.1.")
'192.168.1.41'
>>> getIpAddrForSubnet("192.168.20.")
'192.168.20.200'