[Python-Dev] PEP 563: Postponed Evaluation of Annotations (original) (raw)

Ivan Levkivskyi levkivskyi at gmail.com
Thu Nov 2 15:21:00 EDT 2017

On 2 November 2017 at 18:00, Brett Cannon <brett at python.org> wrote:

On Thu, 2 Nov 2017 at 08:46 Steven D'Aprano <steve at pearwood.info> wrote: On Wed, Nov 01, 2017 at 03:48:00PM -0700, Lukasz Langa wrote: [...snip...] I think the performance bit is really the big deal here. I don't think so. Although subscripting generics is indeed very expensive, this is heavily optimised by various caches. I think PEP 560 might actually have comparable (or even bigger) performance effects.

IIUC performance is listed second in the PEP for a reason. I am OK with using quotes for forward references, but I have seen many people complaining about this (especially novices). I think Jukka is right here.

We can't allow all unquoted forward references but those that will still be quoted appear in more advanced situations like bounded type variables and derived generics. But in these cases it is clear that a forward reference appears in runtime context.

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