[Tutor] Please correct my error handling

[Robert Alexander]

I am having an hard time to properly address some errors in external
programs launched by my python code.

Here follows a sample, in which you can see 3 similar “stanzas”, first is
to check behaviour of a well formed external command and is all as
expected, the second shows the same command with an illegal option and
again all behaves as expected. The problem I have is to catch the “non
existing command” as per the third example.

Thank you very much.

Robert

============== test.py
import subprocess

# 1) try a legit (*nix) command
process = subprocess.Popen(
        ['/bin/ls', '-l'],
        stdout=subprocess.PIPE,
        stderr=subprocess.PIPE,
    )
stdout, stderr = process.communicate()
if not stderr:
    print('--No errors--\n', stdout.decode())
else:
    print('--Error found--\n', stderr.decode())

# 2) repeat with an illegal option
process = subprocess.Popen(
        ['/bin/ls', '-I'],
        stdout=subprocess.PIPE,
        stderr=subprocess.PIPE,
    )
stdout, stderr = process.communicate()
if not stderr:
    print('--No errors--\n', stdout.decode())
else:
    print('--Error found--\n', stderr.decode())

# 3) repeat with an illegal ;) command
process = subprocess.Popen(
        ['/bin/lsd', '-I'],
        stdout=subprocess.PIPE,
        stderr=subprocess.PIPE,
    )
stdout, stderr = process.communicate()
if not stderr:
    print('--No errors--\n', stdout.decode())
else:
    print('--Error found--\n', stderr.decode())