python - subprocess.Popen().pid return the pid of the parent script

Question

I am trying to run a Python script from another Python script, and getting its pid so I can kill it later.

I tried subprocess.Popen() with argument shell=True', but thepidattribute returns thepid` of the parent script, so when I try to kill the subprocess, it kills the parent.

Here is my code:

proc = subprocess.Popen(" python ./script.py", shell=True)
pid_ = proc.pid
.
.
.
# later in my code

os.system('kill -9 %s'%pid_)

#IT KILLS THE PARENT :(

Answer 1

shell=True starts a new shell process. proc.pid is the pid of that shell process. kill -9 kills the shell process making the grandchild python process into an orphan.

If the grandchild python script can spawn its own child processes and you want to kill the whole process tree then see How to terminate a python subprocess launched with shell=True:

#!/usr/bin/env python
import os
import signal
import subprocess

proc = subprocess.Popen("python script.py", shell=True, preexec_fn=os.setsid) 
# ...
os.killpg(proc.pid, signal.SIGTERM)

If script.py does not spawn any processes then use @icktoofay suggestion: drop shell=True, use a list argument, and call proc.terminate() or proc.kill() -- the latter always works eventually:

#!/usr/bin/env python
import subprocess

proc = subprocess.Popen(["python", "script.py"]) 
# ...
proc.terminate()

If you want to run your parent script from a different directory; you might need get_script_dir() function.

Consider importing the python module and running its functions, using its object (perhaps via multiprocessing) instead of running it as a script. Here's code example that demonstrates get_script_dir() and multiprocessing usage.