keep only one process can run at the same time

one.py

import os
import atexit


def keep_single_process():
    pid = str(os.getpid())
    pidfile = "/tmp/main_coupang.pid"
    if os.path.isfile(pidfile):
        raise Exception("%s already exists, exiting" % pidfile)
    with open(pidfile, 'w') as fp:
        fp.write(pid)

    @atexit.register
    def on_exit():
        os.unlink(pidfile)
        
if __name__ == '__main__':
    keep_single_process()
    print(1 + 2)
    print(2 / 0)