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/pull/6086#issuecomment-998973316,https://api.github.com/repos/pydata/xarray/issues/6086,998973316,IC_kwDOAMm_X847ix-E,35968931,2021-12-21T17:43:11Z,2021-12-23T04:12:48Z,MEMBER,"> This is just an internal check in xarray, verifying that _variables is always a Python dict. I would be fine turning this off, certainly at least for tests with the new custom mapping.

It seems I can [make that check pass](https://github.com/pydata/xarray/pull/6086/commits/0380b062201ee6bda8dd6366b74e4f49e94d0d42) very easily, because this already works somehow, even though they aren't considered subtypes :confused: 

```python
In [1]: from xarray.core.utils import CopyableMutableMapping

In [2]: d = {}

In [3]: isinstance(d, CopyableMutableMapping)
Out[3]: True
```

> I realize that my assertion above isn't quite right — the issue was about `Mapping[Hashable, V]`, not `Dict[Hashable, V]`.

Changing `CopyableMutableMapping[Hashable, Variable]` to `Mapping[Hashable, Variable]` in the type hints for `._construct_direct` and `._replace` gets rid of loads of type errors! Must be because those methods don't actually need to mutate the mapping, so won't complain about `.update` if it's never called on those types.

Still have a bunch of errors like this though

```
xarray/core/dataset.py:785: error: Argument 1 to ""Frozen"" has incompatible type ""CopyableMutableMapping[Hashable, Variable]""; expected ""Mapping[Hashable, Variable]""  [arg-type]
```
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1084220684
https://github.com/pydata/xarray/pull/6086#issuecomment-998226035,https://api.github.com/repos/pydata/xarray/issues/6086,998226035,IC_kwDOAMm_X847f7hz,35968931,2021-12-20T19:56:34Z,2021-12-20T19:56:34Z,MEMBER,"> I can have a look this week!

Thanks, but no rush! I write these comments just as much for my benefit as for anyone else's.

> Would you mind committing the `Hashable` -> `Any` changes?

Sure, just done it in https://github.com/pydata/xarray/pull/6086/commits/1376ed9ffe756feefedd8e07e4068c7614ba39bb, though there might be other places that need it as a result.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1084220684
https://github.com/pydata/xarray/pull/6086#issuecomment-998193097,https://api.github.com/repos/pydata/xarray/issues/6086,998193097,IC_kwDOAMm_X847fzfJ,35968931,2021-12-20T19:04:38Z,2021-12-20T19:04:38Z,MEMBER,"I started adding the test implementation, but when I run the new test I get the exact `isinstance` error I was expecting:

```
ds = <xarray.Dataset>
Dimensions:  ()
Data variables:
    a        int64 0
    b        int64 1

    def _assert_dataset_invariants(ds: Dataset):
>       assert isinstance(ds._variables, dict), type(ds._variables)
E       AssertionError: <class 'xarray.tests.test_dataset.CustomMirroredMapping'>

/home/tom/Documents/Work/Code/xarray/xarray/testing.py:309: AssertionError
```
I *think* that with `@runtime_checkable` then once mypy considers these the same type then this would pass, but I might have completely misunderstood how that works (meaning then we would probably need to relax the isinstance check).","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1084220684
https://github.com/pydata/xarray/pull/6086#issuecomment-998127749,https://api.github.com/repos/pydata/xarray/issues/6086,998127749,IC_kwDOAMm_X847fjiF,35968931,2021-12-20T17:24:43Z,2021-12-20T17:24:43Z,MEMBER,"Thanks @max-sixty . Unfortunately changing `Dict[Hashable, V]` -> `Dict[Any, V]` and `CopyableMutableMapping[Hashable, Variable]` -> `CopyableMutableMapping[Any, Variable]` doesn't seem to help, I just get similar errors but with `Any`:

```
xarray/core/dataarray.py:538: error: Argument 1 to ""_construct_direct"" of ""Dataset"" has incompatible type ""Dict[Any, Variable]""; expected ""CopyableMutableMapping[Any, Variable]""  [arg-type]
xarray/core/dataarray.py:538: note: Following member(s) of ""Dict[Any, Variable]"" have conflicts:
xarray/core/dataarray.py:538: note:     Expected:
xarray/core/dataarray.py:538: note:         @overload
xarray/core/dataarray.py:538: note:         def update(self, other: Mapping[Any, Variable], **kwargs: Variable) -> None
xarray/core/dataarray.py:538: note:         @overload
xarray/core/dataarray.py:538: note:         def update(self, other: Iterable[Tuple[Any, Variable]], **kwargs: Variable) -> None
xarray/core/dataarray.py:538: note:         <1 more overload not shown>
xarray/core/dataarray.py:538: note:     Got:
xarray/core/dataarray.py:538: note:         @overload
xarray/core/dataarray.py:538: note:         def update(self, Mapping[Any, Variable], **kwargs: Variable) -> None
xarray/core/dataarray.py:538: note:         @overload
xarray/core/dataarray.py:538: note:         def update(self, Iterable[Tuple[Any, Variable]], **kwargs: Variable) -> None
``` ","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1084220684