issue_comments: 974588586

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https://github.com/pydata/xarray/pull/5950#issuecomment-974588586 https://api.github.com/repos/pydata/xarray/issues/5950 974588586 IC_kwDOAMm_X846Fwqq 14371165 2021-11-20T04:00:45Z 2021-11-20T04:00:45Z MEMBER

These mypy errors are quite tricky. Any ideas how to solve them? Here's a stripped down example:

```python class DatasetReduce2(Protocol): def reduce(self, func: Callable): ...

class DatasetReductions2: def sum(self: DatasetReduce2, dim: Hashable) -> int: return self.reduce(lambda x: x)

class Test(DatasetReductions2): def init(self, a, b): self.a = a self.b = b

a = Test(1, 2) a.sum("z") Invalid self argument "Test" to attribute function "sum" with type "Callable[[DatasetReduce2, Hashable], int] ```

It's posssible to avoid the failures using the previous import way instead of mixing in directly in the dataset/dataarray class, But I think the typing is simply stripped then instead, so that's no good either.

Interesting reading: https://stackoverflow.com/questions/51930339/how-do-i-correctly-add-type-hints-to-mixin-classes

 
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