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:mod:`atexit` --- Exit handlers
===============================
.. module:: atexit
:synopsis: Register and execute cleanup functions.
.. moduleauthor:: Skip Montanaro <skip@mojam.com>
.. sectionauthor:: Skip Montanaro <skip@mojam.com>
The :mod:`atexit` module defines functions to register and unregister 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.
.. 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.
This function returns *func* which makes it possible to use it as a decorator
without binding the original name to ``None``.
.. function:: unregister(func)
Remove a function *func* from the list of functions to be run at interpreter-
shutdown. After calling :func:`unregister`, *func* is guaranteed not to be
called when the interpreter shuts down.
.. 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.
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