1:mod:`atexit` --- Exit handlers 2=============================== 3 4.. module:: atexit 5 :synopsis: Register and execute cleanup functions. 6 7.. moduleauthor:: Skip Montanaro <skip@pobox.com> 8.. sectionauthor:: Skip Montanaro <skip@pobox.com> 9 10-------------- 11 12The :mod:`atexit` module defines functions to register and unregister cleanup 13functions. Functions thus registered are automatically executed upon normal 14interpreter termination. :mod:`atexit` runs these functions in the *reverse* 15order in which they were registered; if you register ``A``, ``B``, and ``C``, 16at interpreter termination time they will be run in the order ``C``, ``B``, 17``A``. 18 19**Note:** The functions registered via this module are not called when the 20program is killed by a signal not handled by Python, when a Python fatal 21internal error is detected, or when :func:`os._exit` is called. 22 23.. versionchanged:: 3.7 24 When used with C-API subinterpreters, registered functions 25 are local to the interpreter they were registered in. 26 27.. function:: register(func, *args, **kwargs) 28 29 Register *func* as a function to be executed at termination. Any optional 30 arguments that are to be passed to *func* must be passed as arguments to 31 :func:`register`. It is possible to register the same function and arguments 32 more than once. 33 34 At normal program termination (for instance, if :func:`sys.exit` is called or 35 the main module's execution completes), all functions registered are called in 36 last in, first out order. The assumption is that lower level modules will 37 normally be imported before higher level modules and thus must be cleaned up 38 later. 39 40 If an exception is raised during execution of the exit handlers, a traceback is 41 printed (unless :exc:`SystemExit` is raised) and the exception information is 42 saved. After all exit handlers have had a chance to run the last exception to 43 be raised is re-raised. 44 45 This function returns *func*, which makes it possible to use it as a 46 decorator. 47 48 49.. function:: unregister(func) 50 51 Remove *func* from the list of functions to be run at interpreter 52 shutdown. After calling :func:`unregister`, *func* is guaranteed not to be 53 called when the interpreter shuts down, even if it was registered more than 54 once. :func:`unregister` silently does nothing if *func* was not previously 55 registered. 56 57 58.. seealso:: 59 60 Module :mod:`readline` 61 Useful example of :mod:`atexit` to read and write :mod:`readline` history 62 files. 63 64 65.. _atexit-example: 66 67:mod:`atexit` Example 68--------------------- 69 70The following simple example demonstrates how a module can initialize a counter 71from a file when it is imported and save the counter's updated value 72automatically when the program terminates without relying on the application 73making an explicit call into this module at termination. :: 74 75 try: 76 with open("counterfile") as infile: 77 _count = int(infile.read()) 78 except FileNotFoundError: 79 _count = 0 80 81 def incrcounter(n): 82 global _count 83 _count = _count + n 84 85 def savecounter(): 86 with open("counterfile", "w") as outfile: 87 outfile.write("%d" % _count) 88 89 import atexit 90 atexit.register(savecounter) 91 92Positional and keyword arguments may also be passed to :func:`register` to be 93passed along to the registered function when it is called:: 94 95 def goodbye(name, adjective): 96 print('Goodbye, %s, it was %s to meet you.' % (name, adjective)) 97 98 import atexit 99 atexit.register(goodbye, 'Donny', 'nice') 100 101 # or: 102 atexit.register(goodbye, adjective='nice', name='Donny') 103 104Usage as a :term:`decorator`:: 105 106 import atexit 107 108 @atexit.register 109 def goodbye(): 110 print("You are now leaving the Python sector.") 111 112This only works with functions that can be called without arguments. 113