Python 3：子进程导致僵尸

Question

继the popular answers to this question和here指令后，我在python 3中创建了以下代码：

  p1                = subprocess.Popen(["ps", "-e", "-o", "pcpu,args"],           stdout=subprocess.PIPE, stderr=subprocess.PIPE)
  p2                = subprocess.Popen(["cut", "-c", "-132"],   stdin=p1.stdout,  stdout=subprocess.PIPE, stderr=subprocess.PIPE)
  p3                = subprocess.Popen(["awk", "NR>2"],         stdin=p2.stdout,  stdout=subprocess.PIPE, stderr=subprocess.PIPE)
  p4                = subprocess.Popen(["sort", "-nr"],         stdin=p3.stdout,  stdout=subprocess.PIPE, stderr=subprocess.PIPE)
  p5                = subprocess.Popen(["head", "-10"],         stdin=p4.stdout,  stdout=subprocess.PIPE, stderr=subprocess.PIPE)
  ps,err            = p5.communicate()
  psout             = str(ps, 'utf-8')

这个代码在循环中每分钟左右调用一次。与我所相信的相反，这仍然会造成僵尸。我究竟做错了什么？

编辑：运行代码时的僵尸：

$ ps -eo pid,ppid,state,cmd | awk '$3 == "Z"'
14441 11232 Z [ps] <defunct>
14442 11232 Z [cut] <defunct>
14445 11232 Z [sort] <defunct>