Executing a Python script without spawning a new process with subprocess

Question

I'm making a python script (start.py) to run multiple (4) python scripts. My code:

    import subprocess
from time import sleep

y=(0.2)
sleep (y)
subprocess.Popen(["python", 'a1.py'])
sleep (y)
subprocess.Popen(["python", 'a2.py'])
sleep (y)
subprocess.Popen(["python", 'a3.py'])
sleep (y)
subprocess.Popen(["python", 'a4.py'])

When I run start.py the four scripts run in background as I expected, but each one with a process ID. Is it possible to have one PID for all?

And how can I make the start.py run at startup as a service? (i'm using raspberry pi).

is there a reason to run the scripts as subprocesses instead of just importing them and running corresponding functions? — jfs
– jfs, Commented Sep 17, 2015 at 12:55
The really old school way is to write each script so that it execve()s the next, and in your main script begin with execve()ing the first ;) This way you simply replace processes so it's the same PID all over. — Cong Ma
– Cong Ma, Commented Oct 2, 2015 at 22:36
@CongMa: if you can modify the scripts then you should modify them to be able to import them instead e.g., import a1, a2, a3, a4; a1.a1(), a2.a2(), ... (actual names should reflect what modules/functions do) — jfs
– jfs, Commented Oct 3, 2015 at 2:09
I kinda expected that, Stack Overflow being what it is, someone will come up with an answer that uses os.execve() in each script, so the process gets replaced recursively. I tried to pre-empt that ;) Sorry for lowering the already low signal-to-noise ratio. — Cong Ma
– Cong Ma, Commented Oct 4, 2015 at 14:14

Community · Accepted Answer · 2017-05-23 11:58:20Z

3

To run the Python script inline within the same interpreter you can use execfile:

https://docs.python.org/2/library/functions.html#execfile

Python 3 equivalent:

What is an alternative to execfile in Python 3?

To start a script as a background service it is best to use external tool like Linux's systemd or supervisord for this purpose.

edited May 23, 2017 at 11:58

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answered Sep 17, 2015 at 10:50

Mikko Ohtamaa

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Comments

Najeeb Choudhary · Accepted Answer · 2015-10-02 22:29:59Z

-2

you can try this code:

import subprocess
from time import sleep
import sys
y=(0.2)
sleep(y)
subprocess.Popen([sys.executable, 'a1.py'],stdin=subprocess.PIPE)
sleep(y)
subprocess.Popen([sys.executable, 'a2.py'],stdin=subprocess.PIPE)
sleep(y)
subprocess.Popen([sys.executable, 'a3.py'],stdin=subprocess.PIPE)
sleep(y)
subprocess.Popen([sys.executable, 'a4.py'],stdin=subprocess.PIPE)

i recommaned to execute script one by one if all think is good then you can execute above program

answered Oct 2, 2015 at 22:29

Najeeb Choudhary

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1 Comment

jfs Over a year ago

(1) each Popen() does spawn a new process i.e., your code contradict the title of the question (2) if you want to wait for each script to finish then use subprocess.check_call() to run it. (3) you should consider importing the corresponding modules instead of executing them.

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