#!/usr/bin/python # -*- coding: utf-8 -*- from scapy.all import * from time import ctime,sleep import threading TIMEOUT = 4 conf.verb=0 def pro(cc,handle):  dst = "192.168.1." + str(cc)  packet = IP(dst=dst, ttl=20)/ICMP()  reply = sr1(packet, timeout=TIMEOUT)  if not (reply is None):   handle.write(reply.src+" is online"+"\n")   #print reply.src, "is online" def main():  threads=[]  f=open('ip.log','a')  for i in range(2,254):   t=threading.Thread(target=pro,args=(i,f))   threads.append(t)  print "main Thread begins at ",ctime()  for t in threads :   t.start()  for t in threads :   t.join()  print "main Thread ends at ",ctime() if __name__=="__main__" :     main();