Get exit code and stderr from subprocess call

Question

I read up on the functions provided by subprocess - call, check_call, check_output, and understand how each works and differs in functionality from one another. I am curren

Answer 1

Both of the proposed solutions either mix the stdout/stderr, or use Popen which isn't quite as simple to use as check_output. However, you can accomplish the same thing, and keep stdout/stderr separate, while using check_output if you simply capture stderr by using a pipe:

import sys
import subprocess

try:
    subprocess.check_output(cmnd, stderr=subprocess.PIPE)
except subprocess.CalledProcessError as e:
    print('exit code: {}'.format(e.returncode))
    print('stdout: {}'.format(e.output.decode(sys.getfilesystemencoding())))
    print('stderr: {}'.format(e.stderr.decode(sys.getfilesystemencoding())))

In this example, since we captured stderr, it's available in the exception's stderr attribute (without capturing with the pipe, it would just be None).