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/5684#issuecomment-895935131,https://api.github.com/repos/pydata/xarray/issues/5684,895935131,IC_kwDOAMm_X841ZuKb,14371165,2021-08-10T11:02:10Z,2021-08-10T11:15:17Z,MEMBER,"> 
> 
> I noticed this issue because my local mypy version was complaining about:
> `xrtools.py:750: error: Signature of ""open_dataset"" incompatible with supertype ""BackendEntrypoint""`
> 
> Anyone have any ideas why the CI version doesn't complain about this?



The original test function did not have any typing defined. For mypy to do any signature checking either of the inputs or outputs needs to be typed. 

This will throw the supertype error, uncomment `self` to get it passing:
```python
import numpy as np
import xarray as xr
from xarray.backends import BackendEntrypoint

expected = xr.Dataset(
    dict(a=2 * np.arange(5)), coords=dict(x=(""x"", np.arange(5), dict(units=""s"")))
)


class CustomBackend(BackendEntrypoint):
    def open_dataset(
        # self,
        filename_or_obj,
        drop_variables=None,
        **kwargs,
    ) -> xr.Dataset:
        return expected.copy(deep=True)
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,963318000
https://github.com/pydata/xarray/pull/5684#issuecomment-894772597,https://api.github.com/repos/pydata/xarray/issues/5684,894772597,IC_kwDOAMm_X841VSV1,14371165,2021-08-08T09:57:28Z,2021-08-08T09:57:28Z,MEMBER,"I noticed this issue because my local mypy version was complaining about:
`xrtools.py:750: error: Signature of ""open_dataset"" incompatible with supertype ""BackendEntrypoint""`

Anyone have any ideas why the CI version doesn't complain about this?","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,963318000