mirror of https://github.com/python/cpython
128 lines
4.5 KiB
ReStructuredText
128 lines
4.5 KiB
ReStructuredText
:mod:`atexit` --- Exit handlers
|
|
===============================
|
|
|
|
.. module:: atexit
|
|
:synopsis: Register and execute cleanup functions.
|
|
|
|
.. moduleauthor:: Skip Montanaro <skip.montanaro@gmail.com>
|
|
.. sectionauthor:: Skip Montanaro <skip.montanaro@gmail.com>
|
|
|
|
--------------
|
|
|
|
The :mod:`atexit` module defines functions to register and unregister cleanup
|
|
functions. Functions thus registered are automatically executed upon normal
|
|
interpreter termination. :mod:`atexit` runs these functions in the *reverse*
|
|
order in which they were registered; if you register ``A``, ``B``, and ``C``,
|
|
at interpreter termination time they will be run in the order ``C``, ``B``,
|
|
``A``.
|
|
|
|
**Note:** The functions registered via this module are not called when the
|
|
program is killed by a signal not handled by Python, when a Python fatal
|
|
internal error is detected, or when :func:`os._exit` is called.
|
|
|
|
**Note:** The effect of registering or unregistering functions from within
|
|
a cleanup function is undefined.
|
|
|
|
.. versionchanged:: 3.7
|
|
When used with C-API subinterpreters, registered functions
|
|
are local to the interpreter they were registered in.
|
|
|
|
.. function:: register(func, *args, **kwargs)
|
|
|
|
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`. It is possible to register the same function and arguments
|
|
more than once.
|
|
|
|
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.
|
|
|
|
.. warning::
|
|
Starting new threads or calling :func:`os.fork` from a registered
|
|
function can lead to race condition between the main Python
|
|
runtime thread freeing thread states while internal :mod:`threading`
|
|
routines or the new process try to use that state. This can lead to
|
|
crashes rather than clean shutdown.
|
|
|
|
.. versionchanged:: 3.12
|
|
Attempts to start a new thread or :func:`os.fork` a new process
|
|
in a registered function now leads to :exc:`RuntimeError`.
|
|
|
|
.. function:: unregister(func)
|
|
|
|
Remove *func* from the list of functions to be run at interpreter shutdown.
|
|
:func:`unregister` silently does nothing if *func* was not previously
|
|
registered. If *func* has been registered more than once, every occurrence
|
|
of that function in the :mod:`atexit` call stack will be removed. Equality
|
|
comparisons (``==``) are used internally during unregistration, so function
|
|
references do not need to have matching identities.
|
|
|
|
|
|
.. 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:
|
|
with open('counterfile') as infile:
|
|
_count = int(infile.read())
|
|
except FileNotFoundError:
|
|
_count = 0
|
|
|
|
def incrcounter(n):
|
|
global _count
|
|
_count = _count + n
|
|
|
|
def savecounter():
|
|
with open('counterfile', 'w') as outfile:
|
|
outfile.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 only works with functions that can be called without arguments.
|