WindowsError: [Error 5] Access is denied when trying to kill a subprocess (python)

Question

So I have a python script that runs a loop in which it calls a program A through subprocess.Popen waits for its output, then saves the output and then calls it again and so

Answer 1

You are seperating your p.poll() and your p.kill() by 20 seconds. By then the process could have finished. I would suggest moving the time.sleep(20) call around so that you poll and kill happen in the same time frame, to avoid killing a dead process. Below is an example run in iPython showing a similar error when killing a completed process:

In [2]: import subprocess

In [3]: p = subprocess.Popen("dir")

In [4]: p.poll()
Out[4]: 0

In [5]: p.kill()
---------------------------------------------------------------------------
WindowsError                              Traceback (most recent call last)

C:\Users\---\<ipython console> in <module>()

C:\Python26\lib\subprocess.pyc in terminate(self)
    947             """Terminates the process
    948             """
--> 949             _subprocess.TerminateProcess(self._handle, 1)
    950
    951         kill = terminate

WindowsError: [Error 5] Access is denied

Even if you kill directly after a poll that shows the processes is running it can finish before the next line is executed. I would also suggest adding a try-catch block for this exception and if it occurs poll again to see if the process actually completed.