[Python-Dev] Please reject or postpone PEP 526

[Nick Coghlan]

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