Is there a way to handle Window's command line errors?

Question

Part of my code deals with terminating a process with a user input using Window's command prompt. Here's a snippet from my project.

import subprocess

def kill_process():
    # Displays running processes similar to linux 'top' command.
    subprocess.call(['tasklist'])

    cmd = input('\nEnter process name or process ID to kill process: ')
    try:
        # Kills process via user input.
        subprocess.call(['taskkill', '/pid', cmd])
    except:
        print('Invalid process name or ID.\n')
        kill_process()

If the user enters an invalid process name or ID I get this error:

ERROR: The process "user_input" not found.

I believe this error isn't handled by python, but rather by Windows. Therefore, I can't catch the exception and handle it accordingly. When this error is raised it forces my code to exit, which is an issue because I need the code to continue, even threw user error.

I can parse threw the data and get process names / IDs using subprocess.check_output() with something like this;

cmd = input('\nEnter process name or process ID to kill process: ')

if cmd in subprocess.check_output(['tasklist'], encoding='UTF-8'):
    subprocess.call(['taskkill', '/pid', cmd])

but, if possible, I rather avoid this method. I might run into similar errors when dealing with CMD later down the line and parsing through this type of data can become tedious.

Python isn't part of Windows yet you've tagged it with **two** Windows' tags. Your program CANNOT run on any standard Windows' computer. Think **What do you want from a Windows' person, you want a python person**? But having tagged it with professional tags what is this amateur hour stuff. Programmers program and don't use users commands. Do it properly https://www.activexperts.com/admin/scripts/wmi/python/0413/ — Noodles, May 04 '19 at 19:57
How to do it WINDOWS VBS https://stackoverflow.com/questions/36120146/can-anyone-help-me-close-this-program-in-vbscript and VBNET list Windows https://pastebin.com/BfvdFkBq list attributes https://pastebin.com/v2TbfKAS list apps in a console https://pastebin.com/n9H1MBML List Environment https://pastebin.com/rrEyVxFd — Noodles, May 04 '19 at 20:03
If a Python question relates to Windows, then of course it should be tagged as such. This script can run on a standard Windows computer, assuming the OP packages it as a Windows executable via PyInstaller or Py2Exe, or distributes it with portable Python, or simply requires Python to be installed. — Eryk Sun, May 04 '19 at 21:58
Also, implementing a program such as taskkill.exe is an extensive amount of work that maybe the OP isn't prepared to handle. It entails enumerating top-level windows and message-only windows across all window stations and desktops in the session and sending `WM_CLOSE` messages to windows owned by the target process(es) as filtered by PID, name, window title, loaded modules, hosted services, etc. This gives the process a chance to exit gracefully. Merely calling `TerminateProcess` is bad form. — Eryk Sun, May 04 '19 at 21:58

Carcigenicate · Accepted Answer · 2019-05-04T19:23:16.577

2

taskkill returns a non-zero error code if the kill failed, and subprocess.call returns that code. Just check for that instead of using exceptions:

import subprocess

def kill_process():
    cmd = input('\nEnter process name or process ID to kill process: ')

    return_code = subprocess.call(['taskkill', '/pid', cmd])
    print(result)

    # 128 == no such process
    if return_code == 128: 
        print('Invalid process name or ID.\n')
        kill_process()

Note, in Python 3, which you seem to be using, subprocess.run seems to be preferred. sunprocess.call is listed under "Older high-level APIs". Sience run returns a CompletedProcess, you'll need to change the code a bit:

. . .
    comp_proc = subprocess.call(['taskkill', '/pid', cmd])

    if comp_proc.returncode == 128: 
        . . .

edited May 04 '19 at 19:23

answered May 04 '19 at 15:54

Carcigenicate

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I looked a bit into `subprocess.run`. I just wanted to note that return codes are handled a bit differently compared to `subprocess.call`. `run` returns [subprocess.CompleteProcess](https://docs.python.org/3/library/subprocess.html#subprocess.CompletedProcess). If you want to get an exit code you must use `returncode`. For this instance, I would use `subprocess.run(['taskkill', '/pid', cmd]).returncode`. Also, thanks for the insight. I'll start using `run` from this point on. – Legended May 04 '19 at 17:02
@Legended If I remember, I'll add a blurb about that when I get home. – Carcigenicate May 04 '19 at 17:10

Is there a way to handle Window's command line errors?

1 Answers1