On Fri, Sep 27, 2019 at 7:12 PM Eric V. Smith <e...@trueblade.com> wrote:
> > On Sep 27, 2019, at 8:23 PM, Guido van Rossum <gu...@python.org> wrote: > > > On Fri, Sep 27, 2019 at 11:18 AM Serhiy Storchaka <storch...@gmail.com> > wrote: > >> I think it needs an explicit support in the type creation machinery (as >> __slots__ itself has) to support descriptors and slots with the same name. >> > > That would be tough, since __slots__ is currently implemented by creating > a separate descriptor for each slot. > > I do think that it would be nice to have a way to automatically create > __slots__ from annotations. It would be even nicer if that could be done > without copying the class object (as the current state of the art requires: > https://github.com/ericvsmith/dataclasses/blob/master/dataclass_tools.py#L23 > ). > > Thinking aloud, perhaps this could be done by setting __slots__ to a > magical value, e.g. > > class Point: > __slots__ = "__auto__" > x: float > y: float > > I think a sentinel like None or a new typing.use_annotations_for_slots > (need a better name, of course) would be better than a magic string, > especially since strings are iterable. > If `__slots__` is a string, it will be considered the name of the single slot to be created. But we have the namespace of __dunder__ names reserved, so `__slots__ = "__auto__"` should be okay. (But `__slots__ = "auto"` would not be.) I'm not keen on `None`, that looks like it would mean "no slots" (analogous to `__hash__ = None`). > This would be independent from the @dataclass decorator (though the > decorator may have to be aware of the magic value). > > If that's too wacky, we could also use a class keyword argument: > > class Point(slots=True): > x: float > y: float > > (Though arguably that's just as wacky. :-) > > > I like a special value for __slots__. I might look in to the feasibility > of this. > Please do. It sounds simpler than the `(slots=True)` version -- IIRC keyword args to classes are hard to work with. -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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