Fix get_bounds_dim_name regression. (#473)

Handle the case where `lat` and `lat_bounds` have same attributes.

Closes #442

Author: dcherian

cf_xarray/accessor.py

@@ -2296,8 +2296,20 @@ def get_bounds_dim_name(self, key: Hashable) -> Hashable:
         -------
         str
         """
-        (crd_name,) = apply_mapper(_get_all, self._obj, key, error=False, default=[key])
+        # In many cases, the bounds variable has the same attrs as the coordinate variable
+        # So multiple matches are possible.
+        crd_names = apply_mapper(_get_all, self._obj, key, error=False, default=[key])
+
         variables = self._obj._variables
+        filtered = [
+            crd_name for crd_name in crd_names if "bounds" in variables[crd_name].attrs
+        ]
+        if len(filtered) > 1:
+            raise KeyError(
+                f"Received multiple matches for {key!r} that have a bounds attribute: {filtered!r} "
+            )
+
+        (crd_name,) = filtered
         crd = variables[crd_name]
         crd_attrs = crd._attrs
         if crd_attrs is None or "bounds" not in crd_attrs:

cf_xarray/tests/test_accessor.py

@@ -974,6 +974,14 @@ def test_get_bounds_dim_name() -> None:
     assert mollwds.cf.get_bounds_dim_name("longitude") == "bounds"
     assert mollwds.cf.get_bounds_dim_name("lon") == "bounds"
 
+    # Be OK with bounds and coordinates having same attributes
+    # GH442
+    assert vert.cf.get_bounds_dim_name("longitude") == "bnds"
+    ds = vert.copy(deep=True)
+    ds.lat.attrs["standard_name"] = "longitude"
+    with pytest.raises(KeyError):
+        ds.cf.get_bounds_dim_name("longitude")
+
 
 def test_grid_mappings():
     ds = rotds.copy(deep=False)