Execute Bash Command in new Process

Question

I need to get information from a bash command which takes several seconds. I want the rest of program to continue until I get the returncode. I tried to do it with multiprocessing but I cant get the returncode of the subprocess alltough the console prints the correct returncode.

from multiprocessing import Process, Value
import subprocess

num = Value("d", 0.0)

class foo(object):
    def __init__(self):
        self.createProcess()

    def createProcess(self):
        p = Process(target=self.Process, args=(num,))
        p.start()
        ...Do Stuff here in parallel...

    def Process(self,n):
        somebashParam = int(n.value)
        p = subprocess.Popen("some -command"+str(somebashParam),shell=True)
        out, err = p.communicate()
        n.value = p.returncode

why does the console print out the right returncode but I cant grab it?
It seems strange for me to launch a subprocess in a other new Process. Is there a better way?

Daniel · Accepted Answer · 2017-01-08 09:47:43Z

1

External processes automatically run in parallel. If you are only interested in the return code, you don't need any additional code:

n = 23
process = subprocess.Popen(["some", "-command", str(n)])
while process.poll() is None:
    do_something_else()
result = process.wait()

answered Jan 8, 2017 at 9:47

Daniel

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5 Comments

hek2mgl Over a year ago

Why do you poll the process? Wouldn't it make more sense to simply do_something_else() and then process.wait() ?

Daniel Over a year ago

@hek2mgl: it depends on how you want to wait for the result.

hek2mgl Over a year ago

What do you mean?

Dennis Over a year ago

First of all Thank you Daniel that solved my problem. @hek2mgl In my program the rest of the the code is to be repeated until I get the result.So I have to use process.poll(). If the rest of the code only is to be executed once you can use process.wait()

hek2mgl Over a year ago

I see, in that case the poll makes sense.

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