Yes, please add this to the PEP in the rejected ideas section, with the motivation for rejection -- the example can show how to work around it.
On Tue, Apr 16, 2019 at 12:51 AM Michael Sullivan <su...@msully.net> wrote: > On Mon, Apr 15, 2019 at 8:12 PM Nathaniel Smith <n...@pobox.com> wrote: > >> On Mon, Apr 15, 2019 at 5:00 PM Michael Sullivan <su...@msully.net> >> wrote: >> > >> > I've submitted PEP 591 (Adding a final qualifier to typing) for >> discussion to typing-sig [1]. >> >> I'm not on typing-sig [1] so I'm replying here. >> >> > Here's the abstract: >> > This PEP proposes a "final" qualifier to be added to the ``typing`` >> > module---in the form of a ``final`` decorator and a ``Final`` type >> > annotation---to serve three related purposes: >> > >> > * Declaring that a method should not be overridden >> > * Declaring that a class should not be subclassed >> > * Declaring that a variable or attribute should not be reassigned >> >> I've been meaning to start blocking subclassing at runtime (e.g. like >> [2]), so being able to express that to the typechecker seems like a >> nice addition. I'm assuming though that the '@final' decorator doesn't >> have any runtime effect, so I'd have to say it twice? >> >> @typing.final >> class MyClass(metaclass=othermod.Final): >> ... >> >> Or on 3.6+ with __init_subclass__, it's easy to define a @final >> decorator that works at runtime, but I guess this would have to be a >> different decorator? >> >> @typing.final >> @alsoruntime.final >> class MyClass: >> ... >> >> This seems kinda awkward. Have you considered giving it a runtime >> effect, or providing some way for users to combine these two things >> together on their own? >> >> Nothing else in typing does any type of runtime enforcement, so I'd be > reluctant to start here. > > One approach would be doing something like this (maybe in a support > module): > if typing.TYPE_CHECKING: > from typing import final > else: > from alsoruntime import final > > So that at checking time, the typechecker would use the typing final but > at runtime we'd get something that does enforcement. > (And for the pre-3.6 case, you could maybe use something like > six.add_metaclass in order to specify the metaclass as a decorator.) > > I can add this as an example to the PEP. > > -sully > > >> -n >> >> [1] https://github.com/willingc/pep-communication/issues/1 >> [2] https://stackoverflow.com/a/3949004/1925449 >> >> -- >> Nathaniel J. Smith -- https://vorpus.org >> > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > https://mail.python.org/mailman/options/python-dev/guido%40python.org > -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him/his **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
_______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
