how to kill process and child processes from python?

you should use signal parameter 9 to kill the process tree.

root@localhost:~$ python
>>> import os
>>> os.kill(pid, 9)

if you should use signal.SIGKILL constant, you should use os.killpg(pgid, signal.SIGKILL) to kill the process tree.

If the parent process is not a "process group" but you want to kill it with the children, you can use psutil (https://psutil.readthedocs.io/en/latest/#processes). os.killpg cannot identify pid of a non-process-group.

import psutil

parent_pid = 30437   # my example
parent = psutil.Process(parent_pid)
for child in parent.children(recursive=True):  # or parent.children() for recursive=False
    child.kill()
parent.kill()

Another solution if your process is not a process group and you don’t want to use psutil, is to run this shell command:

pkill -TERM -P 12345

For instance with

os.system('pkill -TERM -P {pid}'.format(pid=12345))

None of answers can helped me, so I made some research and wrote my answer:
you can easily do it using os module, but it is platform sensitive. This mean that some commands are availiable only on Unix, some – on any platform.
So my project starts one Process, and several Child processes in the different places and times. Some of Child starts Grand-Child Processes 🙂
So I found this solution:

import os
import signal
import platform
# get the current PID for safe terminate server if needed:
PID = os.getpid()
if platform.system() is not 'Windows':
    PGID = os.getpgid(PID)
if platform.system() is not 'Windows':
    os.killpg(PGID, signal.SIGKILL)
else:
    os.kill(PID, signal.SIGTERM)

I use SIGKILL on Linux, to kill process immediatly, and SIGTERM on Windows, because there is no SIGKILL on it.
Also I used killpg() to kill the whole group of processes on Linux.

P.S. Check on Linux, but still doesn’t check on Windows, so maybe we need one more additional command for Windows (for example CTRL_C_EVENT or use another answer.)

I don’t know if this is what you asked for, but if you wish to kill other processes of your application and they were all created using multiprocessing package you can do something like this:

import multiprocessing
from time import sleep

...

def on_shutdown():
    for child in multiprocessing.active_children():
        print('Terminating', child)
        child.terminate()
        sleep(0.5)

def kill_children_processes(pid):
    # TODO: Find a way to not have to use a kill -9.
    processes = os.popen("ps -ej | grep -i 'python' | grep -v 'grep' | awk '{ print $2,$3 }'").read()
    processes = [p.split(" ") for p in processes.split("n")[:-1]]
    processes = "n".join([child for child, parent in processes if parent == str(pid) and child != str(pid)])
    if processes:
        logger.debug(f"Killing ghost processes {processes}")
        os.system(f"kill -9 {processes}")