[Python-ideas] A better (simpler) approach to PEP 505

[Robert Vanden Eynde]

The default could be at the end with an argument to unboxing :

favorite = NoneAware(cfg).user.profile.food.unbox("Spam")


Le lun. 23 juil. 2018 à 17:26, Paul Moore <p.f.moore at gmail.com> a écrit :

> On 23 July 2018 at 16:12, David Mertz <mertz at gnosis.cx> wrote:
> > The need addressed by PEP 505 is real; it's also MUCH more niche and
> > uncommon than something that would merit new syntax.  Moreover, the
> actual
> > legitimate purpose served by the PEP 505 syntax is easily served by
> existing
> > Python simply by using a wrapper class.
> >
> > Here is a way of solving the "deep attribute access to messy data"
> problem
> > that is:
> >
> > (1) Much more explicit
> > (2) Requires no change in syntax
> > (3) Will not be a bug magnet
> > (4) Inasmuch as there are semantic traps, they are announced by the use
> of a
> > class whose documentation would be pointed to for readers
>
> [...]
>
> > I haven't implemented the equivalent dictionary lookups in the below.
> That
> > would be straightforward, and I'm sure my 5 minute throwaway code could
> be
> > improved in other ways also.  But something better than this in the
> standard
> > library would address ALL the actual needs described in PEP 505.  Even
> the
> > pattern Steve Dower is especially fond of like:
> >
> > favorite = cfg?.user?.profile?.food ?? "Spam"
> >
> >
> > (i.e. a configuration may be incomplete at any level, if levels are
> missing
> > default favorite food is Spam).  We could simply spell that:
> >
> > favorite = NoneAware(cfg, "Spam").user.profile.food.unbox()
>
> Thank you. That's the sort of "what would this look like if
> implemented as a library rather than language syntax" solution that I
> had in mind with my earlier post.
>
> I would be very interested to hear discussion of the pros and cons of
> adding new syntax to the language as per PEP 505 in comparison to a
> solution like this (ultimately more fleshed out and "production
> quality") rather than comparisons PEP 505 to raw "roll your own"
> Python code.
>
> For me:
>
> * Library solution works with all versions of Python
> * The need for unbox is a little ugly, but arguably less so than ?.
> (conceded that's a subjective view)
> * Mixing ?. and . is terser than unboxing and reboxing - but are there
> any real examples where that's needed?
> * Having the default at the beginning rather than at the end doesn't
> follow natural reading order (but again that's pretty subjective)
>
> There's little here that isn't subjective, so I expect a lot of heated
> debate that ultimately convinces no-one. But the "you can use this
> solution now" aspect of the library solution seems pretty compelling
> to me - at least in terms of "let's publish the library solution and
> then based on experience with it, review PEP 505".
>
> Paul
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