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Python 2 had a private but usable way of introspecting and manipulating registered atexit handlers by way of the atexit._exithandlers.
In Python 3, registering and unregistering are handled, but there is no longer a way to see what atexit handlers are registered.
Barry suggested filing a bug to have this added as a new feature for Python 3.4. Some kind of read-only sequence would be fine, if the original list can no longer be exposed.

Could you please give an example of why this would be a useful addition?
I can see the usage of removing a handler, but the user should know which handlers are registered.

Barry advised me to open this issue as it's a functional regression from Python 2.
My use case is unit testing code that registers atexit handlers and making sure the right handlers are registered with the correct parameters.

> Barry advised me to open this issue as it's a functional regression from Python 2.
But it was relying on a private and non documented feature in Python
2, so it's not really a regression.
> My use case is unit testing code that registers atexit handlers and making sure the right handlers are registered with the correct parameters.
IMO, complicating an API for testing purpose is a bad idea.

I can think of other use cases. Anyway, I'm just glad your opinion isn't the only one there is ;-)

I don't think you want your test suite to run your atexit handlers at exit, so you should probably mock atexit.register instead.

On Feb 22, 2013, at 06:54 PM, Charles-François Natali wrote:
>Charles-François Natali added the comment:
>
>> Barry advised me to open this issue as it's a functional regression from
>> Python 2.
>
>But it was relying on a private and non documented feature in Python
>2, so it's not really a regression.
I also suggested it would have to be considered a new feature for 3.4.

See also issue32082.