On Fri, Sep 25, 2020 at 11:50 PM Steven D'Aprano <steve@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

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