On Oct 4, 2019, at 12:34, Caleb Donovick <donov...@cs.stanford.edu> wrote:
>
> Allowing key value pairs in geitem need not change the interface of getitem.
> All the key value pairs could be collected as a dict and passed to getitem
> as the index. Similar to how the all the positional arguments are gather into
> a single tuple.
> ```
> class Foo:
> def __getitem__(self, idx):
> print(idx)
>
> f = Foo()
> f[x=1, y=2] # {'x': 1, 'y': 2}
> ```
> This would make any legacy code using normal dicts as keys (I don't know how
> prevalent that is) automatically work with the new syntax.
>
> There doesn't necessarily need to be support for mixing of tuple based
> indexing and keyword indexing. i.e.
> ```
> obj[0, x=1] # SyntaxError
I think it might be better if it actually passed them as keyword arguments.
Then, using the syntax with existing objects would raise a TypeError saying
that the type doesn’t take keyword arguments, instead of saying that dict can’t
be converted to an int or something else less clear.
Also, I think there are user implementations that accept any iterable, whether
to treat it as a tuple or as an array-like, and a dict is an iterable of its
keys, so it might do the wrong thing rather than raising at all.
It would be a bit weird that what look like positional arguments are actually a
tuple, but what look like keyword arguments are keyword arguments, but I don’t
think that’s too bad.
Maybe it would help if you showed a realistic __getitem__ that did the existing
type-switching to handle slice, ellipsis, thing with __index__, or tuple of the
above, and then also did the switching on dict or also took **kwargs. I suspect
that either way, it would turn out that most of the complexity is due to the
existing complicated interface of __getitem__ and keywords don’t make it much
different. But I’m not sure that would be true. And I think many of the
objections are from people who suspect the opposite.
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