Mailing List Archive

Jonathan Polley <jwpolley@collins.rockwell.com> wrote:
: I would like to propose adding a function to the module 'sys' that would
: change (slightly) the behavior of sys.exitfunc. I would like to add a
: method that performs the same function as UNIX's 'atexit ()' function.
: The reason is that I have some modules that would like to do some
: cleanup when python terminates, but I don't want to have to add the code
: required for them to remember the previous value of sys.exitfunc so they
: can call that function (if present). A method sys.atexit () would work
: nicely. It would allow me to add a series of exit functions and be
: guaranteed that they would all be called at the termination of python
: (so I can close files, purge queues, close sockets, etc.). Does anyone
: else think this would be a good idea???

Files and sockets will be closed (and flushed), and if you have a queue
it is problem an instance of a class and an appropriate __del__ method
can be created.

import os
class LockFile:
os_remove = os.remove # do not rely on os still existing
def __del__(self):
if self.locked:
self.os_remove(self.file)

Then if the os module is destroyed during exit clean-up, my class (and
the instances) still have access to the functions it needs.

There is little need in the object-oriented world to have atexit
functionality. There used to be some race-condition problems with this
as well (I explained one of them above). However, the C API does have
the function Py_AtExit() which does this (C modules aren't quite the
same as Python modules ;).

But if you want to make a atexit callback subsystem:

class SysAtExit:
def __init__(self):
self.callbacks = []
# the instance is callable itself
def __call__(self, func):
if callable(func):
self.callbacks.append(func)
else:
raise TypeError, "not a callable"
def on_exit(self):
for func in self.callbacks:
func()
import sys
sys.atexit = SysAtExit()
sys.exitfunc = sys.atexit.on_exit
del SysAtExit, sys

Then in your own code, call:
sys.atexit(my_func_to_call_at_exit)

There is (almost) always a way. ;)

-Arcege