Chris Angelico wrote: > On Wed, 27 Jul 2022 at 21:54, Mathew Elman mathew.el...@ocado.com wrote: > > I don't see why you couldn't. I guess what they do depends if any of these > > have defaults? Which I think they do not in this case, right? > > If they were non vanilla dictionaries that had a default e.g. > > class SomeDict(dict): > > def __getitem__(self, item=None): > > return super().__getitem__(item) > > def __contains__(self, item=None): > > return super().__contains__(item) > > > > So Undefined would trigger a default, but only if there is one? > > print(b[1]) would still print Undefined because print's first argument > > doesn't have a default. > > But print doesn't have a first argument - it accepts *args. So > Undefined still counts as an argument, except when there's a default, > at which point it counts as a non-argument?
Yes, I guess you could do it so that for var args it was treated as a non argument? so print(Undefined) == print() ? But that seems even more surprising... > > a in c would be False. > > That is VERY surprising behaviour. For literally any other object, > that would be True. But then, it would be surprising in other ways if > Undefined behaved like a normal object. > > c[a] would return c[None], which would raise an error here because None > > isn't in the mapping > > Again, very surprising, if putting a value into a mapping doesn't > result in that value being in the mapping. Yes, compared with other objects, there would need to be some surprising behaviour because it isn't a concept in python already. You could fix this specific problem with mappings by changing Undefined to not be hashable, but that is definitely a bandaid. > > Again, I am not pro this idea, just answering the questions you're asking > > as I see them :) > > Yeah. I think you're doing a great job of showing why this is a bad idea :) I do think the desire to fix the "wrapper not needing to know the defaults of wrapped" problem is admirable. Is this the right approach? No, I think not. _______________________________________________ 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/4VIQAKFNSKE7BV54NF3DGC4VNTO7BWEJ/ Code of Conduct: http://python.org/psf/codeofconduct/
