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Send IP at server:

#!/usr/bin/python
import socket, struct, fcntl
def get_ip(iface):
     sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
     sockfd = sock.fileno()
     SIOCGIFADDR = 0x8915
     ifreq = struct.pack('16sH14s', iface, socket.AF_INET, '\x00'*14)
     try:
         res = fcntl.ioctl(sockfd, SIOCGIFADDR, ifreq)
     except:
         return None
     ip = struct.unpack('16sH2x4s8x', res)[2]
     return socket.inet_ntoa(ip)
serverip=get_ip('eth1')
#print serverip
MCAST_GRP = '224.1.1.1'
MCAST_PORT = 5007
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 2)
sock.sendto(serverip, (MCAST_GRP, MCAST_PORT))

Receive IP at client:

#!/usr/bin/python
import socket, struct
MCAST_GRP = '224.1.1.1'
MCAST_PORT = 5007
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sock.bind(('', MCAST_PORT))  # use MCAST_GRP instead of '' to listen only
                             # to MCAST_GRP, not all groups on MCAST_PORT
mreq = struct.pack("4sl", socket.inet_aton(MCAST_GRP), socket.INADDR_ANY)
sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
while True:
  print sock.recv(1024)

eth1: ethernet

wlan0: wifi