f = open("IP-out.txt",'r') all_ip = f.read().splitlines() s_all = set(all_ip) f1=open("not-scan-ip.txt",'r') out_ip = f1.read().splitlines() s_out = set(out_ip) new = s_all.difference(s_out) newlist = sorted(new) f.close() f1.close() f2 = open("IP-out.txt",'w') for i in newlist: f2.write(i+'\n') print i f2.close()