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

[Skip Montanaro]

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

While writing my message I thought, "I'll bet the first question asked will
be about unregistering exit functions."  I've been using the module I
appended to my message unchanged for a couple years and never needed such
functionality.  I'm sure there are applications that could use it, but I
think they'd be a small minority.  Since the only defined interface is a
single registration function (_run_exitfuncs is only used internally), I
think you'd be free to add some unregister function protocol at a later
time if it was deemed necessary.

    David> Also, I'd change:

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

    David> to:

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

    David> Or some such.

register_exitfunc is only meant to be called by clients of the module, not
used internally.  You're assuming that if something else was already bound
to sys.exitfunc that it's not _run_exitfuncs.  With your try/finally code
try the following (mentally is fine):

    import exit
    def foo():
        print 1
    exit.register_exitfunc(foo)
    reload(exit)

I think you'll see that exit._run_exitfuncs is on its own list of exit
functions.  That could be bad.

The setup code:

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

is meant to avoid doing anything if any other module beat us to
sys.exitfunc.  Perhaps it should just be

    sys.exitfunc = _run_exitfuncs

If someone fails to use the defined protocol, screw 'em... ;-)

Skip