On 23 July 2018 at 16:12, David Mertz <me...@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 _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
