Frequently I need to launch sub processes from Python. Sometimes these processes don’t work as expected, and end up blocking the program. If you want to launch a command from python, and cut it off after a certain amount of time, I recommend the threading module.

Here is how to limit the command to running for roughly 5 seconds:

#!/usr/bin/env python
import commands
import datetime
import time
import threading

class runCommand(threading.Thread):
    def run(self):
        status, output = commands.getstatusoutput('sleep 8')

if __name__ == "__main__":
    startTime = datetime.datetime.now()
    maximumRunTime = datetime.timedelta(seconds = 5)
    mythread = runCommand()
    mythread.start()

    while 1:
        if mythread.isAlive():
            print "Thread has not returned yet..."
        else:
            print "Thread is all done."
            break

        if (datetime.datetime.now() - startTime) > maximumRunTime:
            print "Thread has ran too long, giving up."
            break

        time.sleep(1)

    print "Program done"

So when we enter main, I assign the current time to startTime. Then I define maximumRunTime as a difference of 5 seconds. The thread is started, and every second we check to see if it is still running. If it is, we go ahead and check how much real time has elapsed.

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