find_ip.py

def find_ip ():
   # we get a UDP-socket for the TEST-networks reserved by IANA.
   # It is highly unlikely, that there is special routing used
   # for these networks, hence the socket later should give us
   # the ip address of the default route.
   # We're doing multiple tests, to guard against the computer being
   # part of a test installation.

   candidates = []
   for test_ip in ["192.0.2.0", "198.51.100.0", "203.0.113.0"]:
      s = socket.socket (socket.AF_INET, socket.SOCK_DGRAM)
      s.connect ((test_ip, 80))
      ip_addr = s.getsockname ()[0]
      s.close ()
      if ip_addr in candidates:
         return ip_addr
      candidates.append (ip_addr)

   return candidates[0]