How to test whether a host is reachable?

[Fabian Steiner]

Hello!

As the subject says I need to test whether a host computer in our 
network is reachable or not. At the moment I simply attempt to connect 
to a given port that is open when the machine is online:

[...]
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
try:
     sock.connect(('192.168.0.100', 80))
except socket.error:
     print >>sys.stderr "Server offline"
sock.close()
[...]

Now I am wondering if there isn't any better method which would be more 
general. In fact, I think of something like a python version of ping 
which only tries to send ICMP packets. However, I don't know what the 
code has to look like then. Any ideas or suggestions?

Thanks,
Fabian