Terminating python script easily

Cameron Simpson cs at zip.com.au
Fri Oct 23 03:01:09 CEST 2009

On 22Oct2009 16:03, Bahadir Balban <bilgehan.balban at gmail.com> wrote:
| On Thu, Oct 22, 2009 at 4:01 PM, Jean-Michel Pichavant
| <jeanmichel at sequans.com> wrote:
| > Balban wrote:
| >> I have a python build script that calls various commands, some using
| >> os.system().
| >>
| >> Often, if I want to terminate the script prematurely, I press ctrl-c,
| >> but I have to do this many times before I can kill the script for
| >> good. I was wondering is there a way that I define a signal handler
| >> and kill the whole thing at once with a single ctrl-c? Perhaps I
| >> should  also call my other scripts with a method other than os.system
| >> () as well?
| >
| > you may want to use subprocess instead of os.system.
| > On catching CTRL+C, you kill all the pid started with subprocess and exit
| > the script smoothly.
| Hmm. OK, this is what I suspected I needed. So no explicit signal
| catching is required I guess.

But the funny thing is that this shouldn't be necessary. On a UNIX
system, ^C sends SIGINT to all the processes in the process group on the
terminal. Only those who have specially caught SIGINT will fail to exit.

Of course, plenty of programs do catch SIGINT for tidy-up purposes, but
all who do should be tidying up and then exiting promptly.

Unless the subprocess module specially protects its children from SIGINT
I would _hope_ they'd all just quit. Obviously that's not the case

I don't speak with knowledge of what subprocess does, only knowledge of what
should happen on a UNIX system via ^C and what _does_ happen on a UNIX system
unless some app goes out of its way to break^Wchange that behaviour.

I do know that ^C doesn't always terminate my threaded python stuff cleanly,
and I think I recall that such stuff is only delivered to the main thread of
a python program, thus requiring special handle to tidy up other stuff.

Cameron Simpson <cs at zip.com.au> DoD#743

No team manager will tell you this; but they all want to see you
come walking back into the pits sometimes, carrying the steering wheel.
        - Mario Andretti

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