From 10ab1237ce77ee518d56e0c8fbf65eaf43523153 Mon Sep 17 00:00:00 2001
From: Maximilian Roos <m@maxroos.com>
Date: Sat, 14 Oct 2023 12:23:39 -0700
Subject: [PATCH] .

---
 xarray/core/dataset.py       | 27 +++++++++++++++++++++++----
 xarray/tests/test_dataset.py |  9 +++++++--
 2 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/xarray/core/dataset.py b/xarray/core/dataset.py
index b55efadcdb2..076c9f51793 100644
--- a/xarray/core/dataset.py
+++ b/xarray/core/dataset.py
@@ -10342,15 +10342,34 @@ def resample(
     def drop_attrs(self) -> Self:
         """
         Removes all attributes from the Dataset and its variables.
+
+        Returns
+        -------
+        Dataset
         """
         # Remove attributes from the dataset
         self = self._replace(attrs={})
 
         # Remove attributes from each variable in the dataset
         for var in self.variables:
-            # variables don't have a `._replace` method, so we copy and then remove. If
-            # we added a `._replace` method, we could use that instead.
-            self[var] = self[var].copy()
-            self[var].attrs = {}
+            # variables don't have a `._replace` method, so we copy and then remove
+            # attrs. If we added a `._replace` method, we could use that instead.
+            if var not in self.indexes:
+                self[var] = self[var].copy()
+                self[var].attrs = {}
+
+        new_idx_variables = {}
+
+        # Not sure this is the most elegant way of doing this, but it works.
+        # (Contributions welcome for a more general "map over all variables, including
+        # indexes" approach.)
+        for idx, idx_vars in self.xindexes.group_by_index():
+            # copy each coordinate variable of an index and drop their attrs
+            temp_idx_variables = {k: v.copy() for k, v in idx_vars.items()}
+            for v in temp_idx_variables.values():
+                v.attrs = {}
+            # maybe re-wrap the index object in new coordinate variables
+            new_idx_variables.update(idx.create_variables(temp_idx_variables))
+        self = self.assign(**new_idx_variables)
 
         return self
diff --git a/xarray/tests/test_dataset.py b/xarray/tests/test_dataset.py
index 67de33ba615..fd575a6171c 100644
--- a/xarray/tests/test_dataset.py
+++ b/xarray/tests/test_dataset.py
@@ -4366,10 +4366,15 @@ def test_drop_attrs(self) -> None:
         # Doesn't change original
         assert_identical(ds, original)
 
-        # Example with variables and coords with attrs, check they're dropped too
+        # Example with variables and coords with attrs, and a multiindex. (arguably
+        # should have used a canonical dataset with all the features we're should
+        # support...)
         var = Variable("x", [1, 2, 3], attrs=dict(x=1, y=2))
         idx = IndexVariable("y", [1, 2, 3], attrs=dict(c=1, d=2))
-        ds = Dataset(dict(var1=var), coords=dict(y=idx)).assign_attrs(a=1, b=2)
+        mx = xr.Coordinates.from_pandas_multiindex(
+            pd.MultiIndex.from_tuples([(1, 2), (3, 4)], names=["d", "e"]), "z"
+        )
+        ds = Dataset(dict(var1=var), coords=dict(y=idx, z=mx)).assign_attrs(a=1, b=2)
         assert ds.coords["y"].attrs != {}
 
         original = ds.copy(deep=True)