The PEP author is unsure about how it works
-------------------------------------------
I wish this statement had come with some context, because the only thing
I'm unsure about is what I'm supposed to be unsure about.
In general—as I haven't been shy of saying—I find the entire idea awful. I recognize you have done sincere and high quality work in arguing for it; it just feels like a very wrong direction for Python.
But bracketing that, I'm probably the person you have in mind in that comment. And it's funny that you write you are unsure what you are supposed to be unsure about, but the very next section is exactly what I had in mind. Of course I don't mean that if implemented the semantics would be ambiguous... rather, the proper "swallowing" of different kinds of exceptions is not intuitively obvious, not even to you, Steve. And if some decision was reached and documented, it would remain unclear to new (or even experienced) users of the feature.
I'm borderline on ?[] right now. Honestly, I think it works best if it
also silently handles LookupError (e.g. for traversing a loaded JSON
dict), but then it's inconsistent with ?. which I think works best if it
handles None but allows AttributeError.
Moreover, at a couple points in your clarification, you say "ignoring descriptors." But ultimately, the language cannot do that. When a programmer writes `obj?.descriptor?.other_descriptor` SOMETHING has to happen (no matter what actually happens within the code of the property).
This can certainly be specified in some unambiguous way, but I believe that any decision made will be strongly counter-intuitive for certain concrete code.