[Python-Dev] Proposal: standard way of defining and executing "atexit" functions...

[David Ascher]

+1 on the idea.  I wonder if it makes sense to publish a mechanism to allow
de-registering of callbacks, or if that's featuritis.

Also, I'd change:

> try:
>     x = sys.exitfunc
> except AttributeError:
>     sys.exitfunc = _run_exitfuncs
> del sys

to:

try:
	register_exitfuncs(sys.exitfunc)
finally:
	sys.exitfunc = _run_exitfuncs

Or some such.

--david

> -----Original Message-----
> From: python-dev-admin@python.org [mailto:python-dev-admin@python.org]On
> Behalf Of Skip Montanaro
> Sent: Monday, June 19, 2000 1:18 PM
> To: python-dev@python.org
> Subject: [Python-Dev] Proposal: standard way of defining and executing
> "atexit" functions...
> Importance: Low
>
>
>
> Python's sys module defines an exitfunc variable that is settable from
> Python scripts.  At exit, that function will be called with no arguments.
> While this is a good start at supporting standard cleanup activities, it
> defines no protocol to be used by modules that wish to use sys.exitfunc,
> which leads to one of two extremes: 1, two modules wishing to
> define cleanup
> functions both clobber sys.exitfunc or 2, to avoid collisions
> they don't use
> the functionality provided.
>
> At an application level this is okay.  Within a single application you can
> define an application-specific protocol to handle the situation.
> Unfortunately, this still leaves Python's core modules without a
> good way to
> register exit functions.
>
> I ran into this problem today.  I would really like the rlcompleter module
> to read and write readline history files from Python.  Reading a history
> file at module startup is no problem, but deciding where to write the
> history file is a problem.  The logical place is at the time
> sys.exitfunc is
> executed.
>
> For my own applications I long ago wrote a very simple module (called
> exit.py, appended to this message) that defines two functions:
>
>     * exit.register_exitfunc takes a function object and a set of optional
>       arguments and appends them to a list.
>
>     * exit._run_exitfuncs is bound to sys.exitfunc and executes the
>       registered exit functions in the order they appear in the list.
>
> I propose exit.py as the starting point for a well-defined protocol for
> modules to register exit functions without collisions.
>
> --
> Skip Montanaro, skip@mojam.com, http://www.mojam.com/,
> http://www.musi-cal.com/
> On June 24th at 8AM, live your life for an hour as Ricky Byrdsong always
> lived
> his - run/walk in the Ricky Byrdsong Memorial 5K or just make a donation:
>     https://www.SignmeupSports.com/Events/Index_Events.asp?EventID=1395
>
>
> """
> allow programmer to define multiple exit functions to be executed upon
> normal
> program termination.
> """
>
> _exithandlers = []
> def _run_exitfuncs():
>     while _exithandlers:
>         func, targs, kargs = _exithandlers[0]
>         apply(func, targs, kargs)
>         _exithandlers.remove(_exithandlers[0])
>
> def register_exitfunc(func, *targs, **kargs):
>     """register a function to be executed upon normal program termination
>
>     arguments are a function object, and zero or more arguments to pass to
>     it.
>     """
>     _exithandlers.append((func, targs, kargs))
>
> import sys
> try:
>     x = sys.exitfunc
> except AttributeError:
>     sys.exitfunc = _run_exitfuncs
> del sys
>
> if __name__ == "__main__":
>     def x1():
>         print "running x1"
>     def x2(n):
>         print "running x2(%s)" % `n`
>     def x3(n, kwd=None):
>         print "running x3(%s, kwd=%s)" % (`n`, `kwd`)
>
>     register_exitfunc(x1)
>     register_exitfunc(x2, 12)
>     register_exitfunc(x3, 5, "bar")
>     register_exitfunc(x3, "no kwd args")
>
>
> _______________________________________________
> Python-Dev mailing list
> Python-Dev@python.org
> http://www.python.org/mailman/listinfo/python-dev
>