On Mon, Aug 3, 2020, 17:13 Guido van Rossum <gu...@python.org> wrote:
> On Mon, Aug 3, 2020 at 1:49 PM Christopher Barker <python...@gmail.com> > wrote: > >> >> Yes, that would be correct. However, the function could instead be >>> defined as: >>> >>> def __getitem__(self, index, /, **kwargs): >>> ... >>> >>> and then there'd be no conflict (as "self" and "index" must be passed >>> positionally). In effect, the naive spelling (which permits self and >>> index to be passed as keywords) would be a subtle bug that could >>> easily be corrected. >>> >> >> sure, but it would be a bug in a LOT of existing code! >> >> I wonder, if this were to be introduced, if the interpreter could have a >> special case that would call __getitem__ in a special way to avoid this bug >> in old code. >> > > Good edge case to consider. But would it really be such a problem? If you > have an existing class like this: > > class C: > def __getitem__(self, index): ... > > c = C() > > then presumably calling `c[1, index=2]` would just be an error (since it > would be like attempting to call the method with two values for the `index` > argument), and ditto for `c[1, 2, 3, index=4]`. The only odd case might be > `c[index=1]` -- but presumably that would be equivalent to `c[(), index=1]` > so it would still fail. > The problem is that knowing what labels are not allowed would require knowing the implementation details of the dunder methods of each individual class, which I don't think is typically considered public API as far as I am aware. >
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