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/3582#issuecomment-559847335,https://api.github.com/repos/pydata/xarray/issues/3582,559847335,MDEyOklzc3VlQ29tbWVudDU1OTg0NzMzNQ==,6213168,2019-11-29T17:10:40Z,2019-11-29T17:10:40Z,MEMBER,"+1 to shoyer - encapsulation is by far the easiest approach.

>> Why can't you initialise whatever you need to upon first access?

> How do you do that?

```python
@xarray.register_dataset_accessor('foo')
class FooAccessor:
    def __init__(self, xarray_obj):
        self.obj = xarray_obj
        # <insert whatever health checks on xarray_obj>
        self.x = something(xarray_obj)

    @property
    def bar(self):
        # snip

    def baz(self):
        # snip
```

The accessor ``__init__`` method will be invoked by xarray the first time you invoke ``array.foo``. 

Note, however, that it is not recommended to put expensive calculations in it, because the object will *possibly* be destroyed and reinitialised every time the array is transformed - or in other words, anything that is not a read-only method/property or a cell update.

I emphasized *possibly* because some transforms may not destroy and recreate your accessor instance, thus potentially causing it to be in a state that is incoherent with the attached xarray object. Every time you invoke a method, you should verify that whatever assumptions you relied upon to generate the state are still valid.","{""total_count"": 1, ""+1"": 1, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,530062582
https://github.com/pydata/xarray/issues/3582#issuecomment-559663153,https://api.github.com/repos/pydata/xarray/issues/3582,559663153,MDEyOklzc3VlQ29tbWVudDU1OTY2MzE1Mw==,1217238,2019-11-29T05:22:29Z,2019-11-29T05:22:29Z,MEMBER,"What about simply wrapping xarray objects internally in your classes, along with utilities for converting to/from xarray objects? When users want to do domain specific stuff they can use your objects, and when they want to do something generic with xarray they can convert by calling a method like `to_xarray`.","{""total_count"": 2, ""+1"": 2, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,530062582
https://github.com/pydata/xarray/issues/3582#issuecomment-559606839,https://api.github.com/repos/pydata/xarray/issues/3582,559606839,MDEyOklzc3VlQ29tbWVudDU1OTYwNjgzOQ==,6213168,2019-11-28T21:36:39Z,2019-11-28T21:36:39Z,MEMBER,Give a careful read to #3268 if statefulness (beyond what can be stored in xarray variables) is important for you. ,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,530062582
https://github.com/pydata/xarray/issues/3582#issuecomment-559606279,https://api.github.com/repos/pydata/xarray/issues/3582,559606279,MDEyOklzc3VlQ29tbWVudDU1OTYwNjI3OQ==,6213168,2019-11-28T21:32:23Z,2019-11-28T21:32:23Z,MEMBER,"I would not advise subclassing. In most cases it should work but it's thoroughly untested and I would be unsurprised if you were to find a use case that accidentally reverts your subclass to the base class.

I don't think I fully understand your problem with accessors. Is it because you would need a hook that is triggered by ``DataArray. __init__``? Why can't you initialise whatever you need to upon first access? ","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,530062582