"atexit" --- 종료 처리기
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The "atexit" module defines functions to register and unregister *exit
handlers*: functions that are automatically executed "at exit", that
is, upon normal program termination (for instance, if "sys.exit()" is
called or the main module's execution completes) or, more generally,
upon *interpreter shutdown*.

At exit, all registered exit handlers are called in the *reverse*
order in which they were registered. If you register "A", "B", and
"C", at interpreter shutdown time they will be run in the order "C",
"B", "A". 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 an exit handler, a
traceback is printed (unless "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.

In programs that use multiple interpreters, each interpreter has its
own stack of exit handlers, which are executed when the interpreter
shuts down (for example, with
"concurrent.interpreters.Interpreter.close()" or the C API
"Py_EndInterpreter()"). Registration functions in this module only
affect the interpreter they are called from.

**Note:** Exit handlers 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 "os._exit()" is called.

**Note:** The effect of registering or unregistering functions from
within a cleanup function is undefined.

경고:

  When writing exit handlers, especially in C API extensions, keep in
  mind that other exit handlers may still run arbitrary Python code
  after you clean up. Such code should succeed or fail with an
  exception, rather than crash.

버전 3.12에서 변경: Attempts to start a new thread or "os.fork()" a
new process in an exit handler now leads to "RuntimeError".
Previously, this could cause race conditions between the main Python
runtime thread freeing thread states while internal "threading"
routines or the new process try to use that state, which could lead to
crashes rather than clean shutdown.

버전 3.7에서 변경: When used with subinterpreters, registered
functions are local to the interpreter they were registered in.

atexit.register(func, *args, **kwargs)

   Register *func* as an exit handler. Any optional arguments that are
   to be passed to *func* must be passed as arguments to "register()".
   It is possible to register the same function and arguments more
   than once.

   이 함수는 *func* 을 반환하므로 데코레이터로 사용할 수 있습니다.

atexit.unregister(func)

   Remove *func* from the list of exit handlers. "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 "atexit" call stack will be removed.  Equality
   comparisons ("==") are used internally during unregistration, so
   function references do not need to have matching identities.

더 보기:

  모듈 "readline"
     Useful example of "atexit" to read and write "readline" history
     files.


"atexit" Example
================

다음의 간단한 예제는, 모듈이 임포트 될 때 파일에서 카운터를 읽고 프로
그램이 종료할 때 프로그램의 명시적인 호출에 의존하지 않고 카운터의 변
경된 값을 자동으로 저장하는 방법을 보여줍니다.:

   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)

위치 및 키워드 인자가 등록된 함수가 호출될 때 전달되도록 "register()"
에 전달할 수 있습니다:

   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')

*데코레이터* 로 사용하기:

   import atexit

   @atexit.register
   def goodbye():
       print('You are now leaving the Python sector.')

이 방법은 인자 없이 호출할 수 있는 함수에서만 작동합니다.
