Python: How to quit CLI when stuck in blocking raw_input?

Question

I have a GUI program which should also be controllable via CLI (for monitoring). The CLI is implemented in a while loop using raw_input. If I quit the program via a GUI close button, it hangs in raw_input and does not quit until it gets an input.

How can I immediately abort raw_input without entering an input?

I run it on WinXP but I want it to be platform independent, it should also work within Eclipse since it is a developer tool. Python version is 2.6.

I searched stackoverflow for hours and I know there are many answers to that topic, but is there really no platform independent solution to have a non-blocking CLI reader?

If not, what would be the best way to overcome this problem?

Thanks

Helvetii

"without pressing an additional key to get out of the raw_input?" What does this mean? Can you explain what you mean by this? End-of-file is a key. Control-C to kill the program is a key. What is the "additional" key you're worried about? Please be specific. – Meagre

To quit the program I can either enter 'quit' in the CLI or close it via GUI. If I quit the program via GUI, the CLI hangs in raw_input until I enter something in the CLI. How can I immediately abort raw_input without the need to enter an input? – Helvetii

@ S.Lott: I edited the question, please tell me if it is clear now. – Helvetii

"I can either enter 'quit' in the CLI or close it via GUI"? That sounds like a toweringly bad design. You should get rid of the CLI and implement whatever command-response business is going on as a proper part of the GUI. A simple editable text widget is all you need. But CLI + non-CLI user interface is a recipe for disaster. Why are you doing it this way? – Meagre

It was mainly out of historical reasons, the program and the GUI was already finished then a CLI was required, so I implemented it in the console thinking that this would be the simplest way. I'll think about that. – Helvetii

Another reason is that the program is only used company internal as a dev tool and it was more important to have maximum flexibility than useability. – Helvetii

Running into the same issue, I've posted my solution here – Wexford

Answer 1

That's not maybe the best solution but you could use the thread module which has a function thread.interrupt_main(). So can run two thread : one with your raw_input method and one which can give the interruption signal. The upper level thread raise a KeyboardInterrupt exception.

import thread
import time

def main():
    try:
        m = thread.start_new_thread(killable_input, tuple())
        while 1:
            time.sleep(0.1) 
    except KeyboardInterrupt:
        print "exception" 

def killable_input():
    w = thread.start_new_thread(normal_input, tuple())
    i = thread.start_new_thread(wait_sometime, tuple())


def normal_input():
    s = raw_input("input:")


def wait_sometime():
    time.sleep(4) # or any other condition to kill the thread
    print "too slow, killing imput"
    thread.interrupt_main()

if __name__ == '__main__':
    main()

Boudreau

If I'm right, exceptions cannot be handled before raw_input is finished. So it is still an input needed and after that, the exception can be handled. I already tried to throw an exception from another thread. – Helvetii

Maybe it doesn't on windows because this code works on linux (if so then forget what I said). – Boudreau

You are right, using 'thread.interrupt_main()' it does also work on Windows. Thanks! – Helvetii

Answer 2

Depending on what GUI toolkit you're using, find a way to hook up an event listener to the close window action and make it call win32api.TerminateProcess(-1, 0).

For reference, on Linux calling sys.exit() works.

Ot

I call sys.exit() but the problem is that exit waits for raw_input to end which does not happen before I press another key. – Helvetii

@christian Ah, you're on Windows (just read the question again). Will update answer. – Ot

Thank you very much, that will do it. But is there really no platform independent solution to have a non-blocking CLI reader? – Helvetii

@christian I'm not much of a Windows dev, so I can't say for sure. But if sys.exit() doesn't work for you, there is no other built-in Python function. – Ot