Python: Howto launch a full process not a child process and retrieve the PID

Question

I would like:

1. Launch a new process (myexe.exe arg1) from my process (myexe.exe arg0)
2. Retrieve the PID of this new process (os windows)
3. when I

Answer 1

So if I understand you right the code should go like this:

from subprocess import Popen, PIPE
script = "C:\myexe.exe"
param = "-help"
DETACHED_PROCESS = 0x00000008
CREATE_NEW_PROCESS_GROUP = 0x00000200
pid = Popen([script, param], shell=True, stdin=PIPE, stdout=PIPE, stderr=PIPE,
            creationflags=DETACHED_PROCESS | CREATE_NEW_PROCESS_GROUP)

At least I tried this one and worked for me.

Answer 2

To start a child process that can continue to run after the parent process exits on Windows:

from subprocess import Popen, PIPE

CREATE_NEW_PROCESS_GROUP = 0x00000200
DETACHED_PROCESS = 0x00000008

p = Popen(["myexe.exe", "arg1"], stdin=PIPE, stdout=PIPE, stderr=PIPE,
          creationflags=DETACHED_PROCESS | CREATE_NEW_PROCESS_GROUP)
print(p.pid)

Windows process creation flags are here

A more portable version is here.

Answer 3

I did similar a couple of years ago on windows and my issue was wanting to kill the child process.

I presume you can run the subprocess using pid = Popen(["/bin/mycmd", "myarg"]).pid so I'm unsure what the real issue is, so I'm guessing it's when you kill the main process.

IIRC it was something to do with the flags.

I can't prove it as I'm not running Windows.

subprocess.CREATE_NEW_CONSOLE
The new process has a new console, instead of inheriting its parent’s console (the default).

This flag is always set when Popen is created with shell=True.

subprocess.CREATE_NEW_PROCESS_GROUP
A Popen creationflags parameter to specify that a new process group will be created. This flag is necessary for using os.kill() on the subprocess.

This flag is ignored if CREATE_NEW_CONSOLE is specified.