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. >
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