python 设置方法超时

#!/usr/bin/python
#-*-coding:utf-8-*-
import os,time,signal,platform,subprocess

class TimeoutError(Exception):
pass

def run_command(cmd, timeout=60):
is_linux = platform.system() == 'Linux'

p = subprocess.Popen(cmd, stderr=subprocess.STDOUT, stdout=subprocess.PIPE, shell=True, preexec_fn=os.setsid if is_linux else None)
t_beginning = time.time()
seconds_passed = 0
while True:
if p.poll() is not None:
break
seconds_passed = time.time() - t_beginning
if timeout and seconds_passed > timeout:
if is_linux:
os.killpg(p.pid, signal.SIGTERM)
else:
p.terminate()
raise TimeoutError(cmd, timeout)
time.sleep(0.1)
return p.stdout.read()

if __name__ == '__main__':
cmd = 'ping www.google.com
timeout = 10
try:
result = run_command(cmd, timeout)
except TimeoutError:
print 'excute command=<%s> timeout after %i' %(cmd,timeout)
else:
print = 'other error'