On Sat, Sep 26, 2020 at 1:51 AM Guido van Rossum <guido@python.org> wrote:
But this requires introspection.

I'm sorry Guido I'm staring at your message and reread mine several times and I don't understand where introspection is required. It seems like all the parser has to do is what it has always done-- pass the arguments to the item dunders and let the chips fall where they may (other than perhaps adjusting the TypeError message that could result). But you don't have to explain to me, I am certain you know what you're talking about.

Anyway: I don't have an opinion on which of the offered possibilities is the best SENTINEL.

But I would also suggest considering adding the Ellipses object, ..., to the list of possibilities. It's a unique value that sort of stands out (though it is Truthy rather than Falsey like None and the empty tuple).

---
Ricky.

"I've never met a Kentucky man who wasn't either thinking about going home or actually going home." - Happy Chandler