Non-blocking raw_input for Python

I needed a way to allow a raw_input() call to time out. In case it's useful to anyone, I wrote this solution which works under Unix-like OS's.

Simply call nonBlockingRawInput("your prompt text", n) where n is the number of seconds you would like the prompt to wait until it times out. If it does time out, it will return with an empty string.

import signal

class AlarmException(Exception):
    pass

def alarmHandler(signum, frame):
    raise AlarmException

def nonBlockingRawInput(prompt='', timeout=20):
    signal.signal(signal.SIGALRM, alarmHandler)
    signal.alarm(timeout)
    try:
        text = raw_input(prompt)
        signal.alarm(0)
        return text
    except AlarmException:
        print '\nPrompt timeout. Continuing...'
    signal.signal(signal.SIGALRM, signal.SIG_IGN)
    return ''

[Edited Aug. 30, 2010 to fix a typo in the function name and generally improve formatting]

[Edited Feb 1, 2022 to add a tad more explanation, since the comments indicate people are still finding this!]

Comments

[Juanjo]

typo error: nonBockingRawInput x nonBlockingRawInput

I also think that signal.alarm(0) is wrong. I needed to comment it in order to make it work.

[Gary Robinson]

Thanks for pointing out the typo in the function name.

But I don't know what to make of your comment about alarm(0). That's there to cancel the alarm once you've typed something in. It works under the Python versions I've tried. (Though note: as my post says at the top, this is only for unix-like OS's.)

See the example in the Python docs at the end of this page: http://docs.python.org/library/signal.html.

Anyone else have any experiences, pro-or-con, on that issue?

Also, if anyone has a version that works for Windows, I'd appreciate hearing about it!

[Heinrich]

Thats' really good stuff.

I have been searching for this for a while. Other recivpies, like http://code.activestate.com/recipes/134892/ are far more ugly!

Best,
Heinrich

[Python for beginners]

Thanks, this code has come in handy for me several times!! Too bad it's not cross-platform...

[Hellmut Weber]

Thanks for this post.
I use it now in a script where this problem bothered me for a long time.
Works on my debian 11 system with Python2.7 and Python 3.9, glad to have found it.

Best regards
Hellmut