How can I get a list of the IP addresses or host names from a local network easily in Python?
It would be best if it was multi-platform, but it needs to work on Mac OS X first, then others follow.
Edit: By local I mean all active addresses within a local network, such as 192.168.xxx.xxx.
So, if the IP address of my computer (within the local network) is 192.168.1.1, and I have three other connected computers, I would want it to return the IP addresses 192.168.1.2, 192.168.1.3, 192.168.1.4, and possibly their hostnames.
If by "local" you mean on the same network segment, then you have to perform the following steps:

Determine your own IP address
Determine your own netmask
Determine the network range
Scan all the addresses (except the lowest, which is your network address and the highest, which is your broadcast address).
Use your DNS's reverse lookup to determine the hostname for IP addresses which respond to your scan.

Or you can just let Python execute nmap externally and pipe the results back into your program.
List of IP addresses/hostnames from local network in Python