atexit— Exit handlers
atexit module defines functions to register and unregister cleanup
functions. Functions thus registered are automatically executed upon normal
atexit runs these functions in the reverse
order in which they were registered; if you register
at interpreter termination time they will be run in the order
Note: The functions registered via this module 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.
Changed in version 3.7: When used with C-API subinterpreters, registered functions are local to the interpreter they were registered in.
register(func, *args, **kwargs)
Register func as a function to be executed at termination. 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.
At normal program termination (for instance, if
sys.exit() is called or
the main module’s execution completes), all functions registered are called in
last in, first out order. The assumption is that lower level modules will
normally be imported before higher level modules and thus must be cleaned up
If an exception is raised during execution of the exit handlers, a traceback is
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.
This function returns func, which makes it possible to use it as a decorator.
unregister(), func is guaranteed not to be called when the interpreter shuts down, even if it was registered more than once.
unregister()silently does nothing if func was not previously registered.
The following simple example demonstrates how a module can initialize a counter from a file when it is imported and save the counter’s updated value automatically when the program terminates without relying on the application making an explicit call into this module at termination.
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)
Positional and keyword arguments may also be passed to
register() to be
passed along to the registered function when it is called:
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')
Usage as a decorator:
import atexit @atexit.register def goodbye(): print("You are now leaving the Python sector.")
This only works with functions that can be called without arguments.