set timeout for a shell command in python

以下就是python調用系統命令設置超時:

1. def TIMEOUT_COMMAND( command, timeout) :
2.     "" "call shell-command and either return its output or kill it
3.     if it doesn't normally exit within timeout seconds and return None" ""
4.     import subprocess , datetime , os , time , signal
5.     cmd = command.split ( " " )
6.     start = datetime .datetime .now ( )
7.     process = subprocess .Popen ( cmd , stdout=subprocess .PIPE , stderr=subprocess .PIPE )
8.     while process.poll ( ) is None :
9.         time .sleep ( 0 .2 )
10.         now = datetime .datetime .now ( )
11.         if ( now - start) .seconds > timeout:
12.             os .kill ( process.pid , signal .SIGKILL )
13.             os .waitpid ( -1 , os .WNOHANG )
14.             return None
15.     return process.stdout .readlines ( )
16. print TIMEOUT_COMMAND(['ping','192.168.0.254'], 3)