115 lines
3.8 KiB
ReStructuredText
115 lines
3.8 KiB
ReStructuredText
:mod:`atexit` --- Exit handlers
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===============================
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.. module:: atexit
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:synopsis: Register and execute cleanup functions.
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.. moduleauthor:: Skip Montanaro <skip@pobox.com>
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.. sectionauthor:: Skip Montanaro <skip@pobox.com>
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--------------
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The :mod:`atexit` module defines functions to register and unregister cleanup
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functions. Functions thus registered are automatically executed upon normal
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interpreter termination. :mod:`atexit` runs these functions in the *reverse*
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order in which they were registered; if you register ``A``, ``B``, and ``C``,
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at interpreter termination time they will be run in the order ``C``, ``B``,
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``A``.
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**Note:** The functions registered via this module are not called when the
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program is killed by a signal not handled by Python, when a Python fatal
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internal error is detected, or when :func:`os._exit` is called.
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.. versionchanged:: 3.7
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When used with C-API subinterpreters, registered functions
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are local to the interpreter they were registered in.
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.. function:: register(func, *args, **kwargs)
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Register *func* as a function to be executed at termination. Any optional
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arguments that are to be passed to *func* must be passed as arguments to
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:func:`register`. It is possible to register the same function and arguments
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more than once.
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At normal program termination (for instance, if :func:`sys.exit` is called or
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the main module's execution completes), all functions registered are called in
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last in, first out order. The assumption is that lower level modules will
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normally be imported before higher level modules and thus must be cleaned up
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later.
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If an exception is raised during execution of the exit handlers, a traceback is
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printed (unless :exc:`SystemExit` is raised) and the exception information is
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saved. After all exit handlers have had a chance to run, the last exception to
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be raised is re-raised.
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This function returns *func*, which makes it possible to use it as a
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decorator.
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.. function:: unregister(func)
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Remove *func* from the list of functions to be run at interpreter shutdown.
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:func:`unregister` silently does nothing if *func* was not previously
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registered. If *func* has been registered more than once, every occurrence
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of that function in the :mod:`atexit` call stack will be removed. Equality
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comparisons (``==``) are used internally during unregistration, so function
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references do not need to have matching identities.
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.. seealso::
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Module :mod:`readline`
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Useful example of :mod:`atexit` to read and write :mod:`readline` history
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files.
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.. _atexit-example:
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:mod:`atexit` Example
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---------------------
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The following simple example demonstrates how a module can initialize a counter
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from a file when it is imported and save the counter's updated value
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automatically when the program terminates without relying on the application
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making an explicit call into this module at termination. ::
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try:
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with open('counterfile') as infile:
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_count = int(infile.read())
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except FileNotFoundError:
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_count = 0
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def incrcounter(n):
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global _count
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_count = _count + n
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def savecounter():
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with open('counterfile', 'w') as outfile:
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outfile.write('%d' % _count)
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import atexit
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atexit.register(savecounter)
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Positional and keyword arguments may also be passed to :func:`register` to be
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passed along to the registered function when it is called::
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def goodbye(name, adjective):
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print('Goodbye %s, it was %s to meet you.' % (name, adjective))
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import atexit
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atexit.register(goodbye, 'Donny', 'nice')
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# or:
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atexit.register(goodbye, adjective='nice', name='Donny')
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Usage as a :term:`decorator`::
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import atexit
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@atexit.register
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def goodbye():
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print('You are now leaving the Python sector.')
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This only works with functions that can be called without arguments.
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