为什么我的ping命令收到使用错误？

Question

这是我的代码：

t5_send_notification

当我运行它时，我得到以下输出：

    def ping_host(self, hostname, ping_cmd='/usr/bin/ping', count=1, timeout=400):
        cmd = [ping_cmd, '-c%s' % count, '-W%s' % timeout, hostname]
        (output, error) = subprocess.Popen(cmd,
                                           stdout=subprocess.PIPE,
                                           stderr=subprocess.PIPE,
                                           shell=True).communicate()
        print ' '.join( cmd )
        print output, error

我认为我对第一个参数/usr/bin/ping -c1 -W400 tools-dev1.example.com Usage: ping [-aAbBdDfhLnOqrRUvV64] [-c count] [-i interval] [-I interface] [-m mark] [-M pmtudisc_option] [-l preload] [-p pattern] [-Q tos] [-s packetsize] [-S sndbuf] [-t ttl] [-T timestamp_option] [-w deadline] [-W timeout] [hop1 ...] destination Usage: ping -6 [-aAbBdDfhLnOqrRUvV] [-c count] [-i interval] [-I interface] [-l preload] [-m mark] [-M pmtudisc_option] [-N nodeinfo_option] [-p pattern] [-Q tclass] [-s packetsize] [-S sndbuf] [-t ttl] [-T timestamp_option] [-w deadline] [-W timeout] destination 做错了，我正在传递给cmd，但是我不知道是什么。如果我将Popen()粘贴到命令行，则效果很好。