How to get both return code and output from subprocess in Python?

Question

While developing python wrapper library for Android Debug Bridge (ADB), I’m using subprocess to execute adb commands in shell. Here is the simplified example:

import subprocess

...

def exec_adb_command(adb_command):
    return = subprocess.call(adb_command)

If command executed propery exec_adb_command returns 0 which is OK.

But some adb commands return not only “0” or “1” but also generate some output which I want to catch also. adb devices for example:

D:gitadb-libtest>adb devices
List of devices attached
07eeb4bb        device

I’ve already tried subprocess.check_output() for that purpose, and it does return output but not the return code (“0” or “1”).

Ideally I would want to get a tuple where t[0] is return code and t[1] is actual output.

Am I missing something in subprocess module which already allows to get such kind of results?

Thanks!

Asked By: Viktor Malyi

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Source

Answer 1

Popen and communicate will allow you to get the output and the return code.

from subprocess import Popen,PIPE,STDOUT

out = Popen(["adb", "devices"],stderr=STDOUT,stdout=PIPE)

t = out.communicate()[0],out.returncode
print(t)
('List of devices attached nn', 0)

check_output may also be suitable, a non-zero exit status will raise a CalledProcessError:

from subprocess import check_output, CalledProcessError

try:
    out = check_output(["adb", "devices"])
    t = 0, out
except CalledProcessError as e:
    t = e.returncode, e.message

You also need to redirect stderr to store the error output:

from subprocess import check_output, CalledProcessError

from tempfile import TemporaryFile

def get_out(*args):
    with TemporaryFile() as t:
        try:
            out = check_output(args, stderr=t)
            return  0, out
        except CalledProcessError as e:
            t.seek(0)
            return e.returncode, t.read()

Just pass your commands:

In [5]: get_out("adb","devices")
Out[5]: (0, 'List of devices attached nn')

In [6]: get_out("adb","devices","foo")
Out[6]: (1, 'Usage: adb devices [-l]n')

Answered By: Padraic Cunningham

How to get both return code and output from subprocess in Python?

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