On Fri, Sep 27, 2019 at 6:41 PM Ricky Teachey <ri...@teachey.org> wrote:
> Here's an idea I was toying with in thinking about the problem this
> evening.
>
> Currently, python complains if you try to add a class member that will
> conflict with a slot:
>
> >>> class C:
> ... __slots__="x"
> ... x=1
> ...
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> ValueError: 'x' in __slots__ conflicts with class variable
>
> What if the slots machinery were changed so that there was a warning
> propagated instead, and the conflicting member value(s) were saved in some
> appropriate place in the class namespace? Maybe something like
> __slot_conflicts__, or something like that.
>
> >>> class C:
> ... __slots__="x"
> ... x=1
> ...
> >>> C.__slot_conflicts__["x"]
> 1
>
> This would give the decorator the opportunity to find the stuff that was
> put in those fields, and sort out the class definition in an expected way.
>
But it would silently do nothing if there was no class decorator to look at
it.
However if we did `__slots__ = "__auto__"` then we might finagle it so that
the initializers could be preserved:
class C:
__slots__ = "__auto__" # or MRAB's suggested __slots__ = ...
x: float = 0.0
y: float = 0.0
I'm not sure what to do with unannotated initializers -- I worry that it's
a slippery slope, since we don't want methods to be accidentally slotified.
But decorated methods may have a variety of types (e.g. class methods,
static methods, properties) and user-defined decorators could do other
things.
So I'd rather keep the rule for auto-slots simple: if there's an annotation
(and it's not `ClassVar[something]`) then it's a slot, otherwise it's a
class variable that can't be shadowed by an instance variable.
--
--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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