python调用tcpdump抓包过滤的方法

#! /usr/bin/python
 
def tcpdump():
 import subprocess, fcntl, os
 # sudo tcpdump -i eth0 -n -s 0 -w - | grep -a -o -E "Host: .*|GET /.*"
 cmd1 = ['tcpdump', '-i', 'eth0', '-n','-B', '4096','-s', '0', '-w', '-']
 cmd2 = ['grep', '--line-buffered', '-a', '-o', '-E', 'Host: .*|GET /.*']
 p1 = subprocess.Popen(cmd1, stdout=subprocess.PIPE)
 p2 = subprocess.Popen(cmd2, stdout=subprocess.PIPE, stdin=p1.stdout)
 
 flags = fcntl.fcntl(p2.stdout.fileno(), fcntl.F_GETFL)
 fcntl.fcntl(p2.stdout.fileno(), fcntl.F_SETFL, (flags | os.O_NDELAY | os.O_NONBLOCK))
 return p2
 
 
def poll_tcpdump(proc):
 #print 'poll_tcpdump....'
 import select
 txt = None
 while True:
 # wait 1/10 second 
 readReady, _, _ = select.select([proc.stdout.fileno()], [], [], 0.1)
 if not len(readReady):
  break
 try:
  for line in iter(proc.stdout.readline, ""):
  if txt is None:
   txt = ''
  txt += line
 except IOError:
  print 'data empty...'
  pass
 break
 return txt
 
 
proc = tcpdump()
while True:
 text = poll_tcpdump(proc)
 if text:
 print '>>>> ' + text