On Thu, Dec 9, 2021 at 12:41 PM MRAB <pyt...@mrabarnett.plus.com> wrote: > > On 2021-12-08 23:39, Chris Angelico wrote: > > On Thu, Dec 9, 2021 at 10:35 AM Paul Moore <p.f.mo...@gmail.com> wrote: > >> > >> On Wed, 8 Dec 2021 at 23:18, Chris Angelico <ros...@gmail.com> wrote: > >> > Part of the problem is that it is really REALLY hard to figure out > >> > what the actual objections are. I asked, and the one clear answer I > >> > got was one subjective opinion that the cognitive load exceeded the > >> > benefit. Great! That's one person's concern. I've responded to that by > >> > clarifying parts of the cognitive load problem, and that's about as > >> > far as that can go. > >> > >> Um, what parts of my response were unclear? I gave 4 specific points, > >> Brendan gave 4 more (there wasn't much overlap with mine, either). > >> > >> Multiple people have mentioned that the proposed syntax is confusing. > >> You don't have to respond to everyone individually, and indeed you > >> shouldn't - it's the cumulative effect that matters. Telling 10 people > >> that their concern "is one person's concern" doesn't address the fact > >> that 10 people felt similarly. And honestly, there's only about 10 > >> active participants in this thread, so even 5 people with reservations > >> about the syntax is still "half the people who expressed an opinion". > > > > I have attempted to explain the syntax. What is confusing? > > > > def f(x=spam): ... > > > > def f(x=>spam): ... > > > > I'm not sure what concerns need to be addressed, because I don't > > understand the concerns. Maybe I'm just getting caught up on all the > > side threads about "deferreds are better" and "it should be a magical > > function instead" and I've lost some of the basics? Feel free to > > repost a simple concern and I will attempt to respond. > > > [snip] > > I haven't been following the thread for some time, but my expectation > would be that: > > def f(x=>spam): > ... > > would behave like: > > _Missing_ = object() > > def f(x=_Missing_): > if x is _Missing_: > x = spam > ...
Yes, broadly so. The differences would be that the signature actually says what the default will be (instead of "<object object at 0xdeadbeef>"), which in turn also means that you can type-check it reliably (for instance, if 'spam' is '[]', then you can show that this argument should always be a list, without having to say "or this specific object"), and there's no need to pollute an outer context with a sentinel value. I prefer to describe it more like: if x was not specified: x = spam even though "was not specified" isn't actually valid Python code. But the nearest equivalent in current code would be a sentinel like that. ChrisA _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/HJJCUG2UHALNQYTJGIHDT7WR2WLTOXRJ/ Code of Conduct: http://python.org/psf/codeofconduct/
