@lisroach Thanks for the update. I've pushed a commit that should fix the failing test_doctest.

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

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I have made the requested changes; please review again.

I am not sure if I could do the boolean check better- somehow in one line? I'm open to advice!

Thanks for all the reviews @mdickinson and @serhiy-storchaka it's been really helpful!

@eric-wieser I believe Serhiy's thinking is correct, it should be (1, 1).
Subclasses of int inherit the same operations of int, and those operations create instances of int (as opposed to creating an instance of the subclass). For example, if we look at the unary plus of int:

>>> class Int(int):
...     pass
...
>>> x = Int(42)
>>> type(+x)
<class 'int'>
>>> type(+True)
<class 'int'>

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

Reviving a comment hidden away above - should operator.index / PyNumber_Index / int->tp_as_number->nb_index call _PyLong_Copy too for consistency?

ISTM, the code is reasonable as-is.

Despite the missing null check and invalid C syntax that works only because of a macro?

Eric, I didn't see your comments prior to merging. See PR 9297 for the cleanup. The part that was fine as-is was using PyTuple_Pack() on two different code paths.

Agreed, the two code paths thing was unimportant. #9297 seems to address all my comments, other than the question about nb_index, which is tangential anyway

Can you note your review on 9297 please.

If that's aimed at me, I don't know what you're asking me to do.

Reviving a comment hidden away above - should operator.index / PyNumber_Index / int->tp_as_number->nb_index call _PyLong_Copy too for consistency?

This is a different issue. And I think that it should not.