How to raise an Exception using the stderr, stdout info of Popen in Python?

Question

I have a script which is configurable and some part of it functions on the systemX correctly while gives an error on the systemY because the command is only known to SystemX.

process = subprocess.Popen (cmd_false, stdout=subprocess.PIPE, stderr=subprocess.PIPE) 
output, error = process.communicate()
print "OUTPUT: ", output
print "ERROR: ", error

OUTPUT:

error: 500 - command cmd_false not found

ERROR:

(Here is nothing printed)

Using a try-except-else mechanism, In spite of encountering this error in the try block and expecting the code to jump into except block, it end up in the else block.

Btw, I have used the following code snippet but it doesn't raise an error since it returns only the exit status of the child process:

if(process.returncode != 0):
         raise Exception()

Answer 1

Script

#!/usr/bin/env python3

import subprocess, sys

def run_command(command: str):
    try:
        output = subprocess.check_output(command, shell=True, stderr=subprocess.STDOUT)
        message = output.decode('utf-8')
        print(f"SUCCESS: {message}")
    except subprocess.CalledProcessError as err:
        message = err.output.decode('utf-8')
        print(f"ERROR: {message}")
        #sys.exit(err.returncode)
    except Exception as error:
        print(f"ERROR: {error}")
        print(f"ERROR: {command}")
        #sys.exit(2)


run_command('ls -la dir_not_exist')
run_command('ls -la dir_exist')

Output

$ python3 test.py 
ERROR: ls: cannot access 'dir_not_exist': No such file or directory

SUCCESS: total 8
drwxr-xr-x 2 user user 4096 Apr 26 11:20 .
drwxrwxr-x 3 user user 4096 Apr 26 11:20 ..
-rw-r--r-- 1 user user    0 Apr 26 11:20 test