New submission from Erik Bray <erik.m.b...@gmail.com>:

In Python 2 it was possible to directly manipulate the list of registered 
atexit handlers through atexit._exithandlers.  Obviously I'm not complaining 
that this went away, as it was an underscored attribute.  But this possibility 
was still useful in the context of testing.

For example, we have a test suite that runs many test cases in subprocesses run 
with multiprocessing.Process.  Since these call os._exit() any atexit handlers 
registered by the code under test are not run.  It's useful, however, to test 
that either

a) Expected atexit handlers ran correctly or
b) No unexpected atexit handlers were registered

To this end we would save and clear atexit._exithandlers, call 
atexit._run_exitfuncs(), then restore the original atexit._exithandlers.

This is not possible on Python 3 since that all lives in the C module state for 
sub-interpreter support.  For the time being it was necessary to work around 
this with a Cython module, but coding around internal extension module 
structures is hardly ideal: 
https://git.sagemath.org/sage.git/diff/src/sage/misc/_context_py3.pyx?id=85b17201255e9919eaa7b5cff367e8bc271c2a3f

I think it would be useful--for testing purposes *only*--to add a 
_get_exitfuncs() function that returns a tuple of the registered handlers, and 
likewise a _set_exitfuncs(handlers) with sets the registered handlers from an 
iterable (the latter being little more than a shortcut for `atexit._clear(); 
for h in handlers: atexit.register(*h)`).

I would propose that these be undocumented internal functions to emphasize that 
they are not how the module should be used in normal circumstances.  At the 
same time it might be worth addressing https://bugs.python.org/issue22867  I 
can provide a patch if this idea is acceptable.

----------
components: Library (Lib)
messages: 306537
nosy: erik.bray
priority: normal
severity: normal
status: open
title: atexit module: allow getting/setting list of handlers directly
type: behavior

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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue32082>
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