Bugfix __getitem__

We need to reset_coords to drop any coordinate variables that xarray
will automatically bring along. This works for the POP case.

I can see a valid use case where we may want to bring some other
non-dimensional cooordinate variables that are not referenced in
any attrs (i.e. xarray's default behaviour). It seems sensible to
expect users to encode that information in an ancillary_variables
attribute.

Author: dcherian

cf_xarray/accessor.py

@@ -789,7 +789,7 @@ def __getitem__(self, key: Union[str, List[str]]):
                 ds = self._obj
 
             if scalar_key and len(varnames) == 1:
-                da = ds[varnames[0]]
+                da = ds[varnames[0]].reset_coords(drop=True)
                 failed = []
                 for k1 in coords:
                     if k1 not in ds.variables:

cf_xarray/tests/test_accessor.py

@@ -89,6 +89,12 @@ def test_getitem_ancillary_variables():
     with pytest.warns(UserWarning):
         anc[["q"]].cf["q"]
 
+    for k in ["ULONG", "ULAT"]:
+        assert k not in popds.cf["TEMP"].coords
+
+    for k in ["TLONG", "TLAT"]:
+        assert k not in popds.cf["UVEL"].coords
+
 
 @pytest.mark.parametrize("obj", objects)
 @pytest.mark.parametrize(