only run a.py by `python a.py`

a.py

from subprocess import Popen
from signal import SIGKILL
from threading import Thread


def sleep(n):
    from time import sleep
    sleep(n)

process = Popen("python b.py", shell=True)
Thread(target=process.wait).start()
sleep(5)
process.send_signal(SIGKILL)

b.py

from time import sleep
from itertools import count


for i in count():
    print(i)
    sleep(1)