On Friday, September 6, 2019, 11:22:08 AM PDT, Rich Smith <r...@hwyl.org> wrote: > On Thu, 5 Sep 2019 at 16:51, Andrew Barnert <abarn...@yahoo.com> wrote: >> You say here “the dict insertion code” does it. Would they mean >> d[key]=d.skip doesn’t insert anything? > Yes. OK, then I go from +0 on your proposal to -1. Constructing dicts with optionally-included values is a bit overly-verbose, no matter which of the dict-construction mechanisms you use, and it comes up pretty often, so sugar to make it less verbose but just as clear... I don't see a burning need for it, but I've got no objections. But a magic value that can never be stored in any dict? That sounds nice at first, but I think once you think it through, it would be a nightmare. Especially when you consider how fundamental dicts are to all of Python. Globals is a dict. Locals is a dict in some contexts, not others (and the set of contexts may even be different in different Python implementations). Instance attributes are a dict on most classes, but not all. Class attributes are a dict. The namespace passed to the metaclass in a class definition is a dict. The values gathered for `**kw` are a dict. And so on. The rest of your answers are consistent with what you'd expect from this "can never go into a dict" design, so I don't have any additional problem with any of them; it's just the fundamental idea that I disagree with. :) But one more comment: >> If so, then how could I put skip in a dict at all? > The intention is that you couldn't. This could raise some implementation > issues! That's putting it mildly. Forget about figuring out how to make `dict` work (which requires understanding the bytecodes and C API functions and so on). Imagine that you're maintaining one of the popular pure-Python alternative `collections.abc.Mapping` types on PyPI, say, `MySortedDict`. Python 3.9 adds `dict.skip`, and your users quite reasonably want you to add the same feature to your type: `MySortedDict.skip is dict.skip`, and passing that as a key or value to insert/update/construction/etc. skips the same way it does for dict. Does the fact that you can't store `dict.skip` in a global, or an attribute of your class, or pass it as a keyword argument, etc. get in the way? > Writing a ConditionalDict type in a similar spirit would be a lot simpler, > though less> convenient to use. I will experiment. If you're interested, it's pretty easy to write an import hook that replaces all dict displays with calls to your type's constructor. That's obviously not something you'd want to use in real-life code, but I've found it useful for playing with ideas like this before. I think one of the repos with a name ending in "hack" at abarnert - Overview will get you 90% of the way there, but I don't remember exactly what's up there.
| | | | | | | | | | | abarnert - Overview abarnert has 102 repositories available. Follow their code on GitHub. | | |
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