[Python-Dev] Please reject or postpone PEP 526 (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Tue Sep 6 12:00:38 EDT 2016

On 6 September 2016 at 14:04, Guido van Rossum <guido at python.org> wrote:

I'm sorry, but we're not going to invent new syntax this late in the game. The syntax proposed by the PEP has been on my mind ever since PEP 484 with very minor variations; I first proposed it seriously on python-ideas over a month ago, we've been debating the details since then, and it's got a solid implementation based on those debates by Ivan Levkivskyi. In contrast, it looks like you just made the "assert x: T" syntax up last night in response to the worries expressed by Mark Shannon, and "assert" sounds a lot like a run-time constraint to me.

That's a fair description, but the notation also helped me a lot in articulating the concepts I was concerned about without having to put dummy annotated functions everywhere :)

Instead, I encourage you to participate in the writing of a separate PEP explaining how type checkers are expected to work (since PEP 526 doesn't specify that). Ivan is also interested in such a PEP and we hope Mark will also lend us his expertise.

Aye, I'd be happy to help with that - I think everything proposed can be described in terms of existing PEP 484 primitives and the descriptor protocol, so the requirements on typecheckers would just be for them to be self-consistent, rather than defining fundamentally new behaviours.

Cheers, Nick.

-- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia

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