:mod:`atexit` --- Exit handlers

===============================

.. module:: atexit

   :synopsis: Register and execute cleanup functions.

.. moduleauthor:: Skip Montanaro <skip@pobox.com>

.. sectionauthor:: Skip Montanaro <skip@pobox.com>

.. versionadded:: 2.0

The :mod:`atexit` module defines a single function to register cleanup

functions.  Functions thus registered are automatically executed upon normal

interpreter termination.

Note: the functions registered via this module are not called when the program

is killed by a signal, when a Python fatal internal error is detected, or when

:func:`os._exit` is called.

.. index:: single: exitfunc (in sys)

This is an alternate interface to the functionality provided by the

``sys.exitfunc`` variable.

Note: This module is unlikely to work correctly when used with other code that

sets ``sys.exitfunc``.  In particular, other core Python modules are free to use

:mod:`atexit` without the programmer's knowledge.  Authors who use

``sys.exitfunc`` should convert their code to use :mod:`atexit` instead.  The

simplest way to convert code that sets ``sys.exitfunc`` is to import

:mod:`atexit` and register the function that had been bound to ``sys.exitfunc``.

.. function:: register(func[, *args[, **kargs]])

   Register *func* as a function to be executed at termination.  Any optional

   arguments that are to be passed to *func* must be passed as arguments to

   :func:`register`.

   At normal program termination (for instance, if :func:`sys.exit` is called or

   the main module's execution completes), all functions registered are called in

   last in, first out order.  The assumption is that lower level modules will

   normally be imported before higher level modules and thus must be cleaned up

   later.

   If an exception is raised during execution of the exit handlers, a traceback is

   printed (unless :exc:`SystemExit` is raised) and the exception information is

   saved.  After all exit handlers have had a chance to run the last exception to

   be raised is re-raised.

   .. versionchanged:: 2.6

      This function now returns *func* which makes it possible to use it as a

      decorator without binding the original name to ``None``.

.. seealso::

   Module :mod:`readline`

      Useful example of :mod:`atexit` to read and write :mod:`readline` history files.

.. _atexit-example:

:mod:`atexit` Example

---------------------

The following simple example demonstrates how a module can initialize a counter

from a file when it is imported and save the counter's updated value

automatically when the program terminates without relying on the application

making an explicit call into this module at termination. ::

   try:

       _count = int(open("/tmp/counter").read())

   except IOError:

       _count = 0

   def incrcounter(n):

       global _count

       _count = _count + n

   def savecounter():

       open("/tmp/counter", "w").write("%d" % _count)

   import atexit

   atexit.register(savecounter)

Positional and keyword arguments may also be passed to :func:`register` to be

passed along to the registered function when it is called::

   def goodbye(name, adjective):

       print 'Goodbye, %s, it was %s to meet you.' % (name, adjective)

   import atexit

   atexit.register(goodbye, 'Donny', 'nice')

   # or:

   atexit.register(goodbye, adjective='nice', name='Donny')

Usage as a :term:`decorator`::

   import atexit

   @atexit.register

   def goodbye():

       print "You are now leaving the Python sector."

This obviously only works with functions that don't take arguments.