On Sat, Sep 26, 2020 at 10:30 PM Ben Rudiak-Gould <benrud...@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
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