You could also do this using just the __init_subclass__ method. Create some
class AddMixin, and use it like:
class _(AddMixin, using=mod.Cls):
...
The AddMixin class is something like:
class AddMixin:
def __init_subclass_(cls, *, using, **kwargs):
super().__init_subclass__(**kwargs)
using.__dict__.update(cls.__dict__)
return None
This is probably buggy, but that's the general idea.
Not sure how people would feel about how this reads, but I think it's not
too bad.
---
Ricky.
"I've never met a Kentucky man who wasn't either thinking about going home
or actually going home." - Happy Chandler
On Thu, Jan 14, 2021 at 7:28 AM Paul Sokolovsky <[email protected]> wrote:
> Hello,
>
> On Thu, 14 Jan 2021 22:19:06 +1100
> Steven D'Aprano <[email protected]> wrote:
>
> > On Thu, Jan 14, 2021 at 02:05:50PM +0300, Paul Sokolovsky wrote:
> >
> > [...]
> > > Semantically, Python can achieve the same with "imperative" syntax
> > > like:
> > >
> > > def mixin_method(self, args):
> > > ...
> > > Cls.mixin_method = mixin_method
> > >
> > >
> > > The question then: what are the best practices in *declarative*
> > > syntax to achieve the same effect in Python? (but of course, unlike
> > > Ruby, there should be explicit syntactic marker that we augment
> > > existing class, not redefine it).
> >
> > def Cls.mixin_method(self, args):
> > ...
> >
> > has been suggested as syntax for adding new methods to an existing
> > class. I would use that occasionally.
>
> Thanks for the info! But I'd say that I like syntax suggested by Chris
> Angelico (which parallels Ruby's syntax) better. It reminds more of the
> original class definition, and it's normal to add more than one
> var/method via mixin/interface, so grouping them together using
> "class ...:" makes sense. But "scoping" problems pops up nonetheless,
> e.g. one would like, but really can't, do following:
>
> import mod
>
> @mixin
> class mod.Cls:
> ...
>
> So, here's the syntax I came to:
>
> @mixin
> class Cls(mod.Cls):
> ...
>
> It literally reads like "let me add a mixin to class Cls
> (specifically, mod.Cls)". IMHO, it's pretty neat. What do you think?
>
> > Even more so, the generalisation:
> >
> > def obj.method(self, args):
> > ...
> >
> > to add a method to any instance, not just to a class.
>
> Nnnnooooo ;-). Instances can't have methods, only classes can.
> Instances can only have instance variable storing a reference to a
> method, which would need to be called (obj.method)(args), remember? ;-).
>
> []
>
> --
> Best regards,
> Paul mailto:[email protected]
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