html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/1097#issuecomment-523898016,https://api.github.com/repos/pydata/xarray/issues/1097,523898016,MDEyOklzc3VlQ29tbWVudDUyMzg5ODAxNg==,5635139,2019-08-22T13:07:44Z,2019-08-22T13:07:44Z,MEMBER,"> The biggest problem is with all the Dataset methods _and accessors_ that return a DataArray, and vice versa. Anybody who wants to create a coupled pair of Dataset and DataArray subclasses will need to hunt down all methods and accessors that return the other class in the pair and override them.

This is correct - functions which convert between `DataArray` & `Dataset` wouldn't retain type. That said, this can still be helpful without the ability to change type.

There's a bigger piece of work which would solve this too, at the cost of abstraction:  have class attributes which define  `_array_type=DataArray` on `Dataset` and similar for `DataArray`. pandas used this

> May I ask what are the practical use cases for subclassing? In several years worth of day-to-day use of xarray I always found that encapsulation felt much more natural.

Right, good question and we should catch ourselves from adding every abstraction. I have one specific use-case we've already found helpful: we have an object that is _mostly_ a Dataset, with the addition of some behaviors and constructors - for example `from_[dataset_x_and_y]` or `assert_invariants`. Alternatives:
- A class which had the dataset as an attribute - but this means 90%+ of object use is `x.data`, and the object can't be passed into methods expecting a dataset. 
  - Prior to using xarray, we frequently used this pattern to aggregate lots of pandas dataframes (and I've seen this in the wild too)
- A normal dataset with some associated functions in a module - but makes discovering the functions harder
- The current state - an object inherited from `Dataset` with methods

We don't use accessors because the behaviors are specific to a class, rather than every xarray object.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,188113943
https://github.com/pydata/xarray/issues/1097#issuecomment-523881963,https://api.github.com/repos/pydata/xarray/issues/1097,523881963,MDEyOklzc3VlQ29tbWVudDUyMzg4MTk2Mw==,5635139,2019-08-22T12:22:02Z,2019-08-22T12:22:26Z,MEMBER,"> Nevermind `__slots__`. I just tried and there is no noticeable speedup.

I had thought the primary saving was memory (and fairly significant with lots of objects)","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,188113943
https://github.com/pydata/xarray/issues/1097#issuecomment-523750630,https://api.github.com/repos/pydata/xarray/issues/1097,523750630,MDEyOklzc3VlQ29tbWVudDUyMzc1MDYzMA==,5635139,2019-08-22T05:12:08Z,2019-08-22T05:12:08Z,MEMBER,"For that case, you could put a breakpoint in and see what's calling it. It is bemusing

For subclass support, you could see whether there are methods that return `DataArray` / `Dataset` rather than `self.__class__`. 
Maybe we could add a generalized test that could run over a number of methods and assert they return a subclass

I think we're in an equilibrium where subclassing isn't supported for most operations, so it's not used, so we don't hear about it's failures. A moderate push could move us out of that equilibrium! ","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,188113943
https://github.com/pydata/xarray/issues/1097#issuecomment-523600557,https://api.github.com/repos/pydata/xarray/issues/1097,523600557,MDEyOklzc3VlQ29tbWVudDUyMzYwMDU1Nw==,5635139,2019-08-21T18:50:22Z,2019-08-21T18:50:22Z,MEMBER,"I think we should be able improve subclass support. (We use it internally at times, mainly for encapsulating logic on specific objects we inherit from `Dataset`). 

@arokem if you're keen to investigate further, would be interesting to know what's happening there. It's possible it's an issue with `DataArray`'s `repr` rather than the subclass itself","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,188113943