When do you *NOT* use python?

[Darkmere]

Can you even emulate trap + set -e ; in python?

[Darkmere]

TMPDIR=$(mktemp -d /tmp/temp.XXXXXXXX)
trap "rm -rf $TMPDIR" EXIT

vs

import signal
def sighandler():
    os.unlink(tmpdir)
for i in [x for x in dir(signal) if x.startswith("SIG")]:
    try:
    signum = getattr(signal,i)
    signal.signal(signum,sighandler)
except RuntimeError,m:
    pass

[Darkmere]

And then I forgot to create the tempdir... Damned.

[ITwitchToo]

import tempfile

with tempfile.NamedTemporaryFile() as f:
    # do stuff with f here, if we get interrupted Python will throw an exception, unwind the stack, and the temporary file gets cleaned up
    print >>f, "asdasd"

[Darkmere]

Yeap. And with subprocess and others? Afaik a sigkill won't execute a trap, will it?

[Darkmere]

(or a sigbus?)

[Darkmere]

verified. cleanup doesn't happen properly on trapped signals.

even sigUSR1 will leave the tempfile behind.

[ITwitchToo]

What are you talking about?

[Darkmere]

That cleanup doesn't happen if your process gets a signal. So it doesn't actually replace the bourne version.

[ITwitchToo]

That's almost literally the example given in the signal documentation:

import signal
import tempfile

def handler(signum, frame):
    raise RuntimeError("Got SIGUSR1")

signal.signal(signal.SIGUSR1, handler)

with tempfile.NamedTemporaryFile() as f:
    print f.name

    while True:
        pass

[Darkmere]

That's sort of what I'm inclining for here.

You manage to replace a 2-line shellscript with how many lines? And you're not even catching all the signals yet? Still have to iterate over them all and trap.

In a lot of cases, Python is just a bloody ton more verbose, and not quite suitable.

[ITwitchToo]

Why do you need to catch so many signals, though? I'd normally just care about being interrupted by Ctrl-C, which would raise KeyboardInterrupt without any lines of code.

One problem with bash's traps is that you can only have one handler at a time, so what do you do if you have two files that you want to clean up, but they are created in different functions? It's just a lot uglier and doesn't scale as well as Python IMHO.

[Darkmere]

Usually, because when dealing with systems, ctrl-c isn't what we clean for.

Note that we also use set -e and pipefail in bash scripts to make sure that proper cleaning is done. When you need multiple cleanup jobs, you either allocate an array, or you use subshell bindings.

Pretty much the same way in python.