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/3959#issuecomment-611967822,https://api.github.com/repos/pydata/xarray/issues/3959,611967822,MDEyOklzc3VlQ29tbWVudDYxMTk2NzgyMg==,35968931,2020-04-10T10:02:39Z,2020-04-10T10:02:39Z,MEMBER,"> A docstring on a constructor is great -- is there a way to do something like that with accessors?

There surely must be some way to do that, but I'm afraid I'm not a docs wizard. However the accessor is still just a class, whose methods you want to document - would it be too unclear for them to hang off each `HaploAccessor.specific_method()`?

> Is there a way to avoid running check_* methods multiple times? 

There is some caching, but you shouldn't rely on it. In #3268 @crusaderky said ""The more high level discussion is that the statefulness of the accessor is something that is OK to use for caching and performance improvements, and not OK for storing functional information like yours.""

> I think those checks could be expensive

> those arrays should meet different dtype and dimensionality constraints

Checking dtype and dimensions shouldn't be expensive though, or is it more than that?

> Well, we do actually have that problem in trying to find some way to represent 2-bit integers with sub-byte data types but I wasn't trying to get into that on this thread. I'll make the title better.

If you have other questions about dtypes in xarray then please feel free to raise another issue about that.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,597475005
https://github.com/pydata/xarray/issues/3959#issuecomment-611719548,https://api.github.com/repos/pydata/xarray/issues/3959,611719548,MDEyOklzc3VlQ29tbWVudDYxMTcxOTU0OA==,35968931,2020-04-09T19:46:50Z,2020-04-09T19:47:45Z,MEMBER,"> All that said, is it still a bad idea to try to subclass Xarray data structures even if the intent was never to touch any part of the internal APIs?

One of the more immediate problems you'll find if you subclass is that xarray internally uses methods like `self._construct_dataarray(dims, values, coords, attrs)` to construct return values, so you will likely find that for a lot of methods you call you will only get back a bare `DataArray`, not the subclass you put in.

You could make custom accessors which perform checks on the input arrays when they get used?
```python
@xr.register_dataset_accessor('haplo')
def HaploDatasetAccessor:
    def __init__(self, ds)
        check_conforms_to_haplo_requirements(ds)
        self.data = ds
    
    def analyse(self):
        ...

ds.haplo.analyse()
```

I'm also wondering whether given that the only real difference (not just by convention) of your desired data structures from xarray's is the dtype, then (if xarray actually offered it) would something akin to pandas' [`ExtensionDtype`](https://pandas.pydata.org/docs/development/extending.html#extensiondtype) solve your problem?","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,597475005