[Python-Dev] PEP 484 update proposal: annotating decorated declarations (original) (raw)

Ivan Levkivskyi levkivskyi at gmail.com
Mon May 15 09:20:26 EDT 2017

On 15 May 2017 at 10:48, Koos Zevenhoven <k7hoven at gmail.com> wrote:

> Here's the proposed text (wordsmithing suggestions in the PR please): > > +Decorators > +---------- > + > +Decorators can modify the types of the functions or classes they > +decorate. Use the decoratedtype decorator to declare the type of > +the resulting item after all other decorators have been applied:: > + > + from typing import ContextManager, Iterator, decoratedtype > + from contextlib import contextmanager > + > + class DatabaseSession: ... > + > + @decoratedtype(Callable[[str], ContextManager[DatabaseSession]]) > + @contextmanager > + def session(url: str) -> Iterator[DatabaseSession]: > + s = DatabaseSession(url) > + try: > + yield s > + finally: > + s.close() > + > +The argument of decoratedtype is a type annotation on the name > +being declared (session, in the example above). If you have > +multiple decorators, decoratedtype must be topmost. The > +decoratedtype decorator is invalid on a function declaration that > +is also decorated with overload, but you can annotate the > +implementation of the overload series with decoratedtype. > + >

Would annotations be set by the decorator? To me, not setting them would seem weird, but cases where the result is not a function could be weird. I also don't see a mention of this only working in stubs. I like Jukka's version, as it has a clear distinction between functions and other attributes. But that might require a language change to provide annotations in a clean manner? Maybe that language change would be useful elsewhere.

With original syntax it is possible to overwrite annotations without language changes. However with Jukka's syntax it looks difficult. A possible pure-Python way could be to insert an item in an enclosing annotations, if an enclosing scope is a class or module scope.

-- Ivan -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20170515/acd23ce9/attachment.html>

More information about the Python-Dev mailing list