Python, subprocess, call(), check_call and returncode to find if a command exists

Question

I've figured out how to use call() to get my python script to run a command:

import subprocess

mycommandline = ['lumberjack', '-sleep all night', '-work all day']
subprocess.call(mycommandline)

This works but there's a problem, what if users don't have lumberjack in their command path? It would work if lumberjack was put in the same directory as the python script, but how does the script know it should look for lumberjack? I figured if there was a command-not-found error then lumberjack wouldn't be in the command path, the script could try to figure out what its directory is and look for lumberjack there and finally warn the user to copy lumberjack into one of those two places if it wasn't found in either one. How do I find out what the error message is? I read that check_call() can return an error message and something about a returncode attribute. I couldn't find examples on how to use check_call() and returncode, what the message would be or how I could tell if the message is command-not-found.

Am I even going about this the right way?

Answer 1

Wow, that was fast! I combined Theodros Zelleke's simple example and steveha's use of functions with abarnert comment about OSError and Lattyware's comment about moving files:

import os, sys, subprocess

def nameandpath():
    try:
        subprocess.call([os.getcwd() + '/lumberjack']) 
        # change the word lumberjack on the line above to get an error
    except OSError:
        print('\nCould not find lumberjack, please reinstall.\n')
        # if you're using python 2.x, change the () to spaces on the line above

try:
    subprocess.call(['lumberjack'])
    # change the word lumberjack on the line above to get an error
except OSError:
    nameandpath()

I tested it on Mac OS-X (6.8/Snow Leopard), Debian (Squeeze) and Windows (7). It seemed to work the way I wanted it to on all three operating systems. I tried using check_call and CalledProcessError but no matter what I did, I seemed to get an error every time and I couldn't get the script to handle the errors. To test the script I changed the name from 'lumberjack' to 'deadparrot', since I had lumberjack in the directory with my script.

Do you see any problems with this script the way it's written?