Another inconsistency is that the case of keyword arguments only would bind the RHS value to the first positional argument, which is the index, and not the value. I think this is what Guido was referring to when he responded talking about introspection being required? Not sure.
in any case, to me that doesn't seem like such a big deal period it might lead to some weird error messages but I'm not sure why it's such a big problem. Maybe it poses a difficulty for type hinting? On Sat, Sep 26, 2020, 6:48 PM Christopher Barker <python...@gmail.com> wrote: > > On Fri, Sep 25, 2020 at 11:50 PM Steven D'Aprano <st...@pearwood.info> > wrote: > >> > >> 1. We have to pass a sentinel to the setitem dunder if there is no > >> positional index passed. > > > I still don't follow this logic -- why can't nothing be passed? The > dunders either require an index or they don't, would that be just like > function calling? So (adapting the example in the PEP: > > obj[spam=1, eggs=2] > # calls type(obj).__getitem__(obj, spam=1, eggs=2) > > This sure seems like the obvious way to handle it. If the class requires a > positional argument > then it will fail with a TypeError. > > This sure seems like the most straightforward way to handle it. > > I'm sure I'm missing something, but reading the PEP, and my own > experiments haven't clarified it for me. > > NOTE: one inconsistency would be that: > > obj[] > > would be a SyntaxError, > > and > > obj[this=x] > > would be a TypeError, if a positional index were expected. but that's > less weird to me than the other incionsisentcies we are introducing for > backward compatibility. > > -CHB > > -- > Christopher Barker, PhD > > Python Language Consulting > - Teaching > - Scientific Software Development > - Desktop GUI and Web Development > - wxPython, numpy, scipy, Cython >
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