issue_comments

At most, I would require using the new method if you want your code to type-check properly.

IIUC, what we're discussing here is adding a new method that treats all sequences the same (__getitem__ won't be touched, except maybe the type hints).

A level down, re the name — I thought .vars might be decent — but potentially it's too similar to .variables — which is a mapping to the actual variables (and can't take multiple selections)

I do think having a Dataset behave similarly to a dict / Mapping is generally good, and allows new users to bring existing understandings around those data structures to the xarray data model.

I recognize that a hashable iterable (e.g. ('a', 'b', 'c') is an annoying corner case, though.

I think avoiding sel is a good idea (but no strong thoughts here).

how about pick_vars or take_vars?

It would be better to have an explicit method for subsetting Dataset variables.

I agree. sel_vars is more clear IMO since subset could apply to the coordinates too e.g. a spatial subset.

We did a similar splitting of functionality recently with drop, into drop_vars and drop_sel.

So this would leave us with:

• sel/drop_sel for indices
• sel_vars/drop_vars for variables

The naming doesn't have an obvious pattern here, which seems non-ideal. I can't think of anything much better at the moment, but perhaps it would help to avoid reusing sel. Maybe get_vars or subset_vars?

I agree, this API is too overloaded. It would be better to have an explicit method for subsetting Dataset variables. Maybe subset or sel_vars?

In early versions of xarray (back when it was called xray), we actually had a select method but I was concerned it was too confusing with indexing: http://xarray.pydata.org/en/v0.1.1/generated/xray.Dataset.select.html#xray.Dataset.select

What's the reasoning for not returning a Dataset when __getitem__ is passed an Iterable like _copy_listed?

The current check uses hashability to determine whether to try to make a DataArray. In theory, you could put a variable with the name ('a', 'b', 'c') into a Dataset.

What's the reasoning for not returning a Dataset when __getitem__ is passed an Iterable like _copy_listed?

Would that be different from ensuring the input is a list?

Moreover, because Dataset__getitem__ is type unstable,

I very much empathize with the pain from methods being type unstable; indeed I think that's one of the biggest benefits of xarray over pandas. Here, it's stable over the same typed inputs. i.e. if supplied with a list, it returns with a dataset, otherwise it returns a DataArray. (or am I missing something?)

it makes it hard to detect this kind of error using mypy

Is there a way in mypy we could use something like overload to specify the above contract here, as an alternative to another method?