> If xarray supports keyword arguments, this would assign to the
> corresponding values.  If it didn't, it would create a new element of the
> Dataset containing "y[a=2, b=3]".  But "y" would continue working as it
> would, only with different values than expected.

Thanks Todd, that's an excellent example of how an unexpected change
could lead to code doing the wrong thing instead of a nice, easy to
diagnose exception.

But if we did add support for this, then xarray might use it, then it's a question of what it means -- I can't see how it would be ambiguous or break anything. though maybe I"m missing something ....

And what I'm missing might be this: Jonatha's proposal is designed to make it easy for:

[x=4, y=5]

to make a little immutable mapping that can be used as a dict key. essentially shorthand for what you now have to do with:

[CustomImmutableMapping(x=4, y=5)]

But the problem with that is that if a class wants to use keyword indexing in a different way, then it would require extra effort to do so.

-CHB