Develop Reference

how to check the child process running of a parent PID in windows?

I need to get the child process running for a parent PID. How can we check from command line?

You can use tasklist in cmd to get the PID's of all the processes running in the system. Another command to achieve the same is:
wmic process get Caption,ParentProcessId,ProcessId

How to kill a MATLAB Batch Process ran by Qt QProcess?

I currently have a Python program that calls a MATLAB script as batch like so:
matlab = QProcess()
matlab.start('matlab -noFigureWindows -batch "cd(users/script_directory/); MyScript.m;"')
#^ command to start MATLAB batch process in CMD
The issue I'm running into is that once this batch process starts, there's no way to kill it. So if my Python app gets force-closed, the MATLAB script keeps running and causes all sorts of issues, meaning I need to kill the process on app close.
I'm calling the MATLAB script as a QProcess and get the following message when I force-close the Python app before the MATLAB script finishes executing:
QProcess: Destroyed while process ("matlab") is still running.
With this, how do I stop the batch MATLAB process? Using 'ctrl-c' in CMD works for me sometimes to kill the process but I need it to be consistent to make the Python work right.
Similarly, can I just have it 'force quit' or 'restart' batch MATLAB or anything along those lines to clear all running processes?

A brute force way to kill it would be to just kill any matlab process via the process and system utilities library at the start of your application:
import psutil
for process in psutil.process_iter():
if process.name().lower() == 'matlab.exe':
process.terminate()

Python multiprocessing: Running a process after its parent exited

I'm writing a Python program that runs under Mac OS and Linux, and I want to run some logic in a multiprocessing.Process. That logic will take a while, and I want it to continue running even after my program is finished and has exited. i.e., I want the main process to not wait for the auxiliary process to finish. I want the main process to exit as soon as it's finished.
I made a few experiments, and it seems that this behavior is the default when using subprocess, but I can't make it happen using multiprocessing.Process, even when I run set_start_method('spawn').
Do you know of a way to get multiprocessing.Process to behave this way?

Looks like starting a new process, and then calling os.fork from it does the trick.

Python script never ends in task scheduler

I am trying to set up a python code to be executed automatically.
I started with a small code to be executed:
import datetime
with open("out.txt","a") as f:
f.write(datetime.datetime.now().isoformat())
The task will start allright, and executes (The file is modified), but it never ends in the task scheduler.
this and this exist in SO, but have no real answer. The only workaround proposed in these threads is to force the end of task after a given time in Windows, but this requires to know how long the python script will take which will not be the case for my actual task.
How can the task scheduler know that a python script is finished ?
I run it the following way in the task scheduler :
program : cmd
arguments : /c C:\python27\python.exe C:\path\of\script.py
execute in : C:\path\of\
I tried some variations around this, like executing python instead of cmd, but it didn't change anything. I had hoped the /c would force the task to close.

as Gaurav Pundir mentioned, adding sys.exit(0) should end the script properly and thus the task. However, you do need to add the sys library with import sys in order to use sys.exit(0). Hope this helps!

it looks like a bug to me.
Try looking up for python console under Task Manager.
if it is not there then the program has exited successfully.
I have the same issue with Windows 10, python script ran successfully, there is no python console under Task Manager, yet the scheduled task Status still says 'Running'

There seems to be no correct fix for such issue with CMD as the intermediate launcher.
There is a [End] command in Task Scheduler GUI, clicking it will always terminate the CMD/batch file leaving the spawned python.exe process to straw.
The real problem: there doesn't seem to be any way for cmd to pass on the terminate signal to python.exe.. and neither can taskengine reliably determine if python.exe is alive or not.

I ran into the same problem, the python file didn't stop in the task scheduler. I imported sys and wrote sys.exit(0) but I still got the same problem.
Finally, I decided to press "Update" which solved my problem; the status of the task was "Ready", and not "Running". For information, I use windows 11.

os.system('exit') in python

My friend is in a macOS environment and he wanted to call os.system('exit') at the end of his python script to make the terminal close. It doesn't. This doesn't surprise me but I would like to know what exactly is going on between the python script and the terminal when this call is made.
In my mental simulation the terminal should have to tell you that there are still running jobs, but that doesn't happen either.
As a side question : will some less common terminals close when a process calls this?

read the help:
Execute the command (a string) in a subshell.
A subshell is launched, and exit is run in that subshell.
To exit the enclosing terminal, you have to kill the parent. One way to do it is:
os.system("kill -9 %d"%(os.getppid())

The system function starts another shell to execute a command. So in this case your Python scripts starts a shell and runs "exit" command in there, which makes that process exit. However, the Python script itself, including a terminal where it is running, continues to run. If the intent is to kill the terminal, you have to get the parent process ID and send a signal requesting it to stop. That will kill both Python script and a terminal.

Remember that system first spawns/forks a sub-shell to execute its commands. In effect, you are asking only the sub-shell to exit.