[issue44123] make function parameter sentinel value true singletons

[Tal Einat]

Tal Einat <taleinat+python at gmail.com> added the comment:

> And what you need is just to not pass to the wrapped function arguments which were not passed to wrapper. *args and **kwargs do not contain arguments which were not passed.

It's common for wrapper functions to mirror the defaults of the wrapped functions and pass those along... A quick search brings up an example from dataclasses where sentinel values are passed as arguments to a wrapped callable[1].

I concede that issues with pickling such values are very unlikely. I stumbled upon such an issue once and it was difficult to debug, but that was a very unusual circumstance.

Still, it's a bit surprising that we have public facing values in stdlib modules which don't behave as one would expect with regard to pickling. This is why I created this 

It seems that I should have marked this as "enhancement" rather than the default of "behavior", though, since I meant this to be an improvement on the current situation, rather then assert the current situation is "broken".

[1] https://github.com/python/cpython/blob/c10c2ec7a0e06975e8010c56c9c3270f8ea322ec/Lib/dataclasses.py#L346

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type: behavior -> enhancement
versions:  -Python 3.10

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