python - Test a pair of network sockets at the same time -

i have app x can run on either of 2 computers, on no more 1 @ once. have app y, written in python, given 2 possible ip addresses needs find out computer running app x (if any). i've partially solved having udp service listens on port , responds 'hello' whenever receives data. client can try , send data app x port on each address , if gets response, know application running on computer.

my code far looks this:

 def ipaddress(self):     """test side responds on status port."""     s = socket.socket(socket.af_inet, socket.sock_dgram)     try:         s.settimeout(5)         s.sendto("status", (addr_a, port))         s.recvfrom(1024)     except socket.timeout:         try:             s.sendto("status", (addr_b, port))             s.recvfrom(1024)         except:             pass         else:             return addr_b     else:         return addr_a     finally:         s.close()     return none 

the problem function it's called periodically whenever want talk computer running app x. test addr_a first, , if it's not running app x have wait socket timeout before trying addr_b. although doesn't happen app x have switched computers whenever come around trying again.

is there better way? i'm wondering if it's possible connect both computers in parallel , return 1 responds? or should cache ip address responded first last time function called? how code these or other ideas?

thanks.

edit: here revised code using select:

def ipaddress(addr_a, addr_b, timeout=5):     """test side responds on status port."""      # create udp sockets each address      socks = [ socket.socket(socket.af_inet, socket.sock_dgram),               socket.socket(socket.af_inet, socket.sock_dgram)               ]      # send data each socket      sock, addr in zip(socks, (addr_a, addr_b)):         sock.connect(addr)  # explicit connect getpeername works         sock.send("status")      # wait first respond if     while socks:         waiting = select.select(socks, [], socks, timeout)[0]         if waiting:             sock in waiting:                 try:                     data = sock.recv(1024)                     if data:                         return sock.getpeername()[0]                 except exception, e:                     # [errno 10054] means socket isn't                     # available, see if other responds instead...                     socks.remove(sock)         else:             break   # timeout occurred     return none 

you should @ select.select() provides capability looking @ 2 computers in parallel.