[Python-ideas] Another use case for the 'lazy' (aka 'delayed') keyword

[David Mertz]

If you'd like help with the PEP, I'd be happy to assist (subject to time,
as always the problem).  I think this idea got pretty good support in the
discussion (of course, I'm biased because it's one of the few proposed here
that I actually really like).  Few core developers really chimed in on the
matter, so it's hard to say what they might opine about the implementation
or supportability.

On Tue, Feb 28, 2017 at 10:08 AM, Joseph Hackman <josephhackman at gmail.com>
wrote:

> Yes I do think this is precisely where a lazy or delayed feature would
> work well. I'm working on writing up a complete PEP now, and have made some
> progress on the things left unsolved in the other thread. I will post again
> when the PEP is closer to complete.
>
> Fundamentally, anything can be done, but I don't think that altering the
> code of others for one case is Pythonic, and though it happens, I think
> there is value in making it less necessary.
>
> Cheers!
> Joseph
>
> > On Feb 28, 2017, at 9:46 AM, Michel Desmoulin <desmoulinmichel at gmail.com>
> wrote:
> >
> >
> >> Le 28/02/2017 à 13:47, Markus Meskanen a écrit :
> >>    You don't need list comprehension, you can use a for loop.
> >>
> >>    You don't need upacking you can use indexing.
> >>
> >>    And you don't need lazy, it's just convenient.
> >>
> >>
> >> With this sole argument you can add almost anything to the language as
> >> long as it has at least one use case where it's better than existing
> >> tools. I'm not against the lazy proposal in general, but attempting to
> >> justify a new keyword to replace this is just silly to me:
> >>
> >> class Config(dict):
> >>    def lazy_get(self, key, callable=None):
> >>        if key in self:
> >>            return self[key]
> >>        return callable(key)
> >
> > With this sole argument you can reject await / async because we could do
> > it with yield from and decorator.
> >
> > With this solve argument you can reject comprehension because we have
> > map and filter.
> >
> > With this solve argument you can reject defauldict because we can code
> > one ourself.
> >
> > I mean come on, a decorator is just:
> >
> > @decorator
> > def decorated():
> >
> > Instead of
> >
> > decorated = decorator(decorated)
> >
> > It's just convenience and elegance.
> >
> > The sweet spot for lazy is a use case where you can't easily modify the
> > code to get your getter and setter. You example again makes the
> > assumption you can easily add such a wrapper. But if you can't, then you
> > have to import it and wrap the config object in every module using it.
> > Test all that. Ensure you don't pass the wrapper by accident to
> > something that would break on it, etc.
> >
> > And how many time do you have to do that ?
> >
> > You will write your wrapper for lists ? And tuples ?
> >
> > And will you test those ? document those ? Explain to others that to get
> > a callable, you need to pass a callable returning a callable ?
> >
> > Then again for your next project or you do a library with all the stuff
> > it implies ?
> >
> > It's neither convenient nor elegant.
> >
> > lazy is not only practical, but it's also beautiful. It reads well. It
> > solves a problem we all have on a regular basis.
> >
> > Yes we can live without it. I mean, Python is already incredibly
> > convenient, of course whatever we suggest now is going to be a cherry on
> > top of the language cake.
> >
> > And yes I got a big mouth because it's a lot of work to implement it and
> > it's work I'm not capable to do since I can't code in C to save my life.
> >
> > Does it removes the merits from lazy ?
> >
> > Wouldn't you like it to just be able to drop "lazy" in your next 3.7
> code ?
> >
> >
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