1 

     2 :mod:`atexit` --- Exit handlers

     3 ===============================

     4 

     5 .. module:: atexit

     6    :synopsis: Register and execute cleanup functions.

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

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

     9 

    10 

    11 .. versionadded:: 2.0

    12 

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

    14 functions.  Functions thus registered are automatically executed upon normal

    15 interpreter termination.

    16 

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

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

    19 :func:`os._exit` is called.

    20 

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

    22 

    23 This is an alternate interface to the functionality provided by the

    24 ``sys.exitfunc`` variable.

    25 

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

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

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

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

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

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

    32 

    33 

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

    35 

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

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

    38    :func:`register`.

    39 

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

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

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

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

    44    later.

    45 

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

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

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

    49    be raised is re-raised.

    50 

    51    .. versionchanged:: 2.6

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

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

    54 

    55 

    56 .. seealso::

    57 

    58    Module :mod:`readline`

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

    60 

    61 

    62 .. _atexit-example:

    63 

    64 :mod:`atexit` Example

    65 ---------------------

    66 

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

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

    69 automatically when the program terminates without relying on the application

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

    71 

    72    try:

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

    74    except IOError:

    75        _count = 0

    76 

    77    def incrcounter(n):

    78        global _count

    79        _count = _count + n

    80 

    81    def savecounter():

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

    83 

    84    import atexit

    85    atexit.register(savecounter)

    86 

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

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

    89 

    90    def goodbye(name, adjective):

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

    92 

    93    import atexit

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

    95 

    96    # or:

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

    98 

    99 Usage as a :term:`decorator`::

   100 

   101    import atexit

   102 

   103    @atexit.register

   104    def goodbye():

   105        print "You are now leaving the Python sector."

   106 

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

   108