mirror of https://github.com/python/cpython
109 lines
3.5 KiB
ReStructuredText
109 lines
3.5 KiB
ReStructuredText
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: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@mojam.com>
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.. sectionauthor:: Skip Montanaro <skip@mojam.com>
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.. versionadded:: 2.0
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The :mod:`atexit` module defines a single function to register cleanup
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functions. Functions thus registered are automatically executed upon normal
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interpreter termination.
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Note: the functions registered via this module are not called when the program
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is killed by a signal, when a Python fatal internal error is detected, or when
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:func:`os._exit` is called.
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.. index:: single: exitfunc (in sys)
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This is an alternate interface to the functionality provided by the
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``sys.exitfunc`` variable.
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Note: This module is unlikely to work correctly when used with other code that
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sets ``sys.exitfunc``. In particular, other core Python modules are free to use
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:mod:`atexit` without the programmer's knowledge. Authors who use
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``sys.exitfunc`` should convert their code to use :mod:`atexit` instead. The
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simplest way to convert code that sets ``sys.exitfunc`` is to import
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:mod:`atexit` and register the function that had been bound to ``sys.exitfunc``.
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.. function:: register(func[, *args[, **kargs]])
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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`.
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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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.. versionchanged:: 2.6
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This function now returns *func* which makes it possible to use it as a
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decorator without binding the original name to ``None``.
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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 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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_count = int(open("/tmp/counter").read())
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except IOError:
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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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open("/tmp/counter", "w").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 obviously only works with functions that don't take arguments.
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