Let me clarify what the typing-sig folks wanted out of this PEP. We only care about adding support for `x[*y]` (including things like `x[a, *b, c]`). We'll just update PEP 646 to add that explicitly there and hope that PEP 646 fares better than PEP 637. To fans of PEP 637 I would call out that the main reason for rejection seems to be this paragraph: The benefits of the new syntax as outlined in the PEP are not particularly

strong, and community support for the new syntax seems low. The new syntax doesn’t provide an obvious way to do something that is currently error-prone, and doesn’t open up new possibilities that were not possible before. While there are certainly cases that could use the new syntax, for many of them it’s not clear that it would be a win, or that third-party libraries would indeed use the syntax. The Steering Council isn’t really convinced by any of the suggested uses in the PEP.

This seems to imply that in order for a proposal like this to fare better in the future, the authors would need to line up support from specific, important communities like the scientific, data science or machine learning communities. Currently such support seems absent except for one specific package (xarray). -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-c...

I think this is really the crux of the rejection: is the new syntax being proposed primarily to support typing, or Python in general? Does it help both, or is one use case the motivating factor, and the other is just piggybacking on the syntactic proposal? Quoting from the rejection email:

The strongest argument for the new syntax comes from the typing side of Python. The Steering Council is not particularly convinced it is of significant benefit to the static type checking language, but even if it were, at this point we’re reluctant to add general Python syntax that only (or mostly) benefits the static typing language. If the syntax would be of great benefit to static typing, it might be time to discuss letting go of the requirement that the typing language be a subset of Python -- but whether this feature is important enough to consider that is up to the typing community.

The SC didn’t find general Python functionality compelling enough, or outweighing the costs. It’s possible that the proposed syntax is really useful for typing, and less compelling for Python users in general. And that’s totally fine, but then we’ll need to discuss whether the typing language and the general Python syntax needs to continue to track. Cheers, -Barry

On Mar 15, 2021, at 13:07, Guido van Rossum wrote:

Let me clarify what the typing-sig folks wanted out of this PEP. We only care about adding support for `x[*y]` (including things like `x[a, *b, c]`). We'll just update PEP 646 to add that explicitly there and hope that PEP 646 fares better than PEP 637.

To fans of PEP 637 I would call out that the main reason for rejection seems to be this paragraph:

The benefits of the new syntax as outlined in the PEP are not particularly strong, and community support for the new syntax seems low. The new syntax doesn’t provide an obvious way to do something that is currently error-prone, and doesn’t open up new possibilities that were not possible before. While there are certainly cases that could use the new syntax, for many of them it’s not clear that it would be a win, or that third-party libraries would indeed use the syntax. The Steering Council isn’t really convinced by any of the suggested uses in the PEP.

This seems to imply that in order for a proposal like this to fare better in the future, the authors would need to line up support from specific, important communities like the scientific, data science or machine learning communities. Currently such support seems absent except for one specific package (xarray).

-- --Guido van Rossum (python.org/~guido) Pronouns: he/him (why is my pronoun here?) _______________________________________________ Python-Dev mailing list -- python-dev@python.org To unsubscribe send an email to python-dev-leave@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/MOXRTWGV... Code of Conduct: http://python.org/psf/codeofconduct/

All right. Thanks for the feedback. Brandt should we terminate the branch, or restructure it for the *args mechanics? On Mon, 15 Mar 2021 at 18:43, Thomas Wouters wrote:

Hi Stefano,

Thank you for submitting PEP 637 (Support for indexing with keyword arguments). The Steering Council has reviewed the PEP and after careful consideration, we have decided to reject the PEP. There are a number of reasons for this, but fundamentally we do not believe the benefit is great enough to outweigh the cost of the new syntax.

The benefits of the new syntax as outlined in the PEP are not particularly strong, and community support for the new syntax seems low. The new syntax doesn’t provide an obvious way to do something that is currently error-prone, and doesn’t open up new possibilities that were not possible before. While there are certainly cases that could use the new syntax, for many of them it’s not clear that it would be a win, or that third-party libraries would indeed use the syntax. The Steering Council isn’t really convinced by any of the suggested uses in the PEP.

The strongest argument for the new syntax comes from the typing side of Python. The Steering Council is not particularly convinced it is of significant benefit to the static type checking language, but even if it were, at this point we’re reluctant to add general Python syntax that only (or mostly) benefits the static typing language. If the syntax would be of great benefit to static typing, it might be time to discuss letting go of the requirement that the typing language be a subset of Python -- but whether this feature is important enough to consider that is up to the typing community.

The SC considers the cost of the new syntax significant. It’s not a natural fit, as shown by the corner cases discussed in the PEP. It’s difficult to teach, as indexing and function calls are not as interchangeable or equivalent as they may appear. Looking at more complex expressions with the new syntax, mentally parsing them is significantly harder than the equivalent without the new syntax, even if it requires more lines of code to do the same thing.

In addition to all that, the SC is worried about the performance of indexing in CPython and in other Python implementations, considering it’s a very common operation, and about the suggested new __getitem__ protocol, particularly the confusing corner cases of indexing with keywords and zero or one positional items. These are not, however, the main reason we decided to reject the PEP.

With our appreciation, For the whole Python Steering Council, Thomas. -- Thomas Wouters

Hi! I'm an email virus! Think twice before sending your email to help me spread!

-- Kind regards, Stefano Borini