I didn't participate in the mailing list discussions for PEP 637, but I have become somewhat involved in the reference implementation and final revisions. While reviewing the PEP, I noticed what I think is a missed opportunity to finally allow empty subscripting (`obj[]`). It seems to me to be a natural consequence of the `obj[*a]` and `obj[**k]` syntax which the PEP proposes, and I'm quite surprised that the PEP still outlaws it (the latest revision has language that says we're punting on this, but I'd like to change that).
I'm wondering how others feel. Do you think we should allow `obj[]` as sugar for `obj[()]`, or leave it a `SyntaxError`? Steven, Stefano, and I are in agreement that we should at least consider allowing it. I didn't see it being discussed much at all (although I may be missing a thread or two). My primary motivation here is type-hinting generics (like `tuple[]`, currently spelled as `tuple[()]`). I'm worried that this could become more of an annoyance with the potential introduction of variadic generics (PEP 646) - not only for end-users who need to add type hints for empty generics, but also for library authors who will constantly need to special-case their reprs to turn `"MyType[]"` into `"MyType[()]"` or similar (I found that even mypy's error messages still don't do this correctly for `tuple` / `Tuple`!). But I don't really have much insight into how pervasive that issue would be, in practice. The way I see it, there are sort of four paths forward: - Add this to PEP 637. **I think this option makes the most sense.** - Add this to the new variadic generics PEP. - Propose this as its own PEP some time after 637 is accepted (sort of like PEP 618). - Don't pursue it, it's a bad idea. The only drawback I anticipate is beginners doing stuff with `some_mapping[]` and being surprised that it's adding/removing/looking up an empty tuple. But to me, `some_mapping[]` being the same as `some_mapping[()]` is no more confusing than `some_mapping[1]` being different from `some_mapping[1,]`. If anything, it's just a good teaching moment, where they can learn that positional indices are treated "as if" they are wrapped in parentheses. Or, for more advanced users, asking them what `x[y=z]` without the keyword argument would mean. Thoughts? Brandt _______________________________________________ Python-ideas mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/[email protected]/message/6PXH6KCVT5PK2G3MR4U5PPYR6AKI3FMR/ Code of Conduct: http://python.org/psf/codeofconduct/
