On Tue, Jun 26, 2018 at 11:34 AM, Franklin? Lee <leewangzhong+pyt...@gmail.com> wrote: > On Wed, Jun 20, 2018, 00:05 Serhiy Storchaka <storch...@gmail.com> wrote: >> >> 19.06.18 22:18, James Edwards пише: >> > I've only recently looked for these special methods, so that in and of >> > itself may be the reason these methods aren't exposed, but I could think >> > of objects that may wish to implement __min__ and __max__ themselves, >> > for efficiency. >> >> There are two questions. >> >> 1. What to do with additional min() and max() arguments: key and default. > > > Neither should be passed to a dunder. > > It is not possible to handle `key` without figuring out if a function is > monotonic (a Turing-complete problem in general) or anti-monotonic (if that > is a real term), so you MUST fall back on full iteration if a key is > provided. > > `default` is only used in case of an empty collection. The only question is, > who has responsibility for detecting an empty collection, and how? > > Caller detects: The caller checks length before calling the dunder. If there > is no dunder, it doesn't check. Are there real-world cases where length is > not defined on an iterable collection? > > Dunder detects: Right now, `max` detects empty by watching for > StopIteration, which can no longer be a false positive. StopIterations from > a deeper scope are wrapped. If the dunder throws an error to signal > emptiness, it should not be thrown otherwise. I think that's impossible to > guarantee.
There's an argument that you DO want to pass to the dunder: `last=True`. It's not currently part of `min` and `max`. Currently, if there are multiple items that are maximum, `max` will return the first one. In the future, a `last:bool` param could be added, and a dunder for `max` will want to handle it. _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
