def checksum(source_string):
    sum = 0
    countTo = (len(source_string)/2)*2
    count = 0
    while count 16)  +  (sum & 0xffff)
    sum = sum + (sum >> 16)
    answer = ~sum
    answer = answer & 0xffff
    answer = answer >> 8 | (answer > 16) + (sum & 0xffff)
        sum = sum + (sum >> 16)

        return (~sum) & 0xffff

    @property
    def __icmpPacket(self):
        '''构造 ICMP 报文'''
        if not self.IPv6:
            header = struct.pack('bbHHh', 8, 0, 0, self.__id, 0) # TYPE、CODE、CHKSUM、ID、SEQ
        else:
            header = struct.pack('BbHHh', 128, 0, 0, self.__id, 0)

        packet = header + self.__data     # packet without checksum
        chkSum = self.__inCksum(packet) # make checksum

        if not self.IPv6:
            header = struct.pack('bbHHh', 8, 0, chkSum, self.__id, 0)
        else:
            header = struct.pack('BbHHh', 128, 0, chkSum, self.__id, 0)

        return header + self.__data   # packet *with* checksum

    def isUnIP(self, IP):
        '''判断IP是否是一个合法的单播地址'''
        IP = [int(x) for x in IP.split('.') if x.isdigit()]
        if len(IP) == 4:
            if (0 < IP[0] < 223 and IP[0] != 127 and IP[1] < 256 and IP[2] < 256 and 0 < IP[3] < 255):
                return True
        return False

    def makeIpPool(self, startIP, lastIP):
        '''生产 IP 地址池'''
        IPver = 6 if self.IPv6 else 4
        intIP = lambda ip: IPy.IP(ip).int()
        ipPool = {IPy.intToIp(ip, IPver) for ip in range(intIP(startIP), intIP(lastIP)+1)}

        return {ip for ip in ipPool if self.isUnIP(ip)}

    def mPing(self, ipPool):
        '''利用ICMP报文探测网络主机存活

        参数：
            ipPool  -- 可迭代的IP地址池
        '''
        Sock = self.__icmpSocket
        Sock.settimeout(self.timeout)
        packet = self.__icmpPacket
        recvFroms = set()   #接收线程的来源IP地址容器

        sendThr = SendPingThr(ipPool, packet, Sock, self.timeout)
        sendThr.start()

        while True:
            try:
                recvFroms.add(Sock.recvfrom(1024)[1][0])
            except Exception:
                pass
            finally:
                if not sendThr.isAlive():
                    break
        return recvFroms & ipPool

if __name__=='__main__':
    s = Nscan()
    ipPool = s.makeIpPool('192.168.0.1', '192.168.0.254')
    print( s.mPing(ipPool) )