On Sat, Sep 26, 2020 at 10:30 PM Ben Rudiak-Gould <benrudiak@gmail.com> wrote:
I don't understand the problem here.
d[p=q] --> d.__{get,set,del}item__((), ..., p=q) d[1, p=q] --> d.__{get,set,del}item__((1), ..., p=q) d[1, 2, p=q] --> d.__{get,set,del}item__((1, 2), ..., p=q) d[1, 2, 3, p=q] --> d.__{get,set,del}item__((1, 2, 3), ..., p=q) d[1, 2, ..., n, p=q] --> d.__{get,set,del}item__((1, 2, ..., n), ..., p=q)
Now obviously the n=1 case is a wart. But the n=0 case isn't a wart. It's just like n=2, n=3, etc.
You can't tell the difference between a single tuple argument and n arguments for any n≠1. As far as I can tell the problem when n=0 is no more or less serious than the problem when n≥2. I don't see the point of adding another special case to the spec when it doesn't even solve the general problem.
The problem is that there is lots of existing code like this: def __setitem__(self, index, value): ... But the new features will almost certainly lead people to write new code like this: d={} obj[**d] = "foo" # no kwd arguments provided here ...which, if someone does this arbitrarily against classes that use the existing kind of code I gave at the first, will call (if the sentinel is () ): obj.__setitem__(()) ...which could have all kinds of weird effects rather than giving an error, as I think would be better. Steven's response to that was essentially "well then, don't unpack dictionaries against arbitrary subscriptable types" which I fully agree is a perfectly legitimate response. But I think having no sentinel at all and instead telling people "either provide a default argument for both index AND value in your __setitem__ method, or neither" is also a perfectly legitimate way forward. Not sure which is better. --- Ricky. "I've never met a Kentucky man who wasn't either thinking about going home or actually going home." - Happy Chandler