keep attrs in idata/datatree conversions

CHANGELOG.md

@@ -8,6 +8,7 @@
 - Fix numpyro jax incompatibility. ([2465](https://github.com/arviz-devs/arviz/pull/2465))
 - Avoid closing unloaded files in `from_netcdf()` ([2463](https://github.com/arviz-devs/arviz/issues/2463))
 - Fix sign error in lp parsed in from_numpyro ([2468](https://github.com/arviz-devs/arviz/issues/2468))
+- Fix attrs persistance in idata-datatree conversions ([2476](https://github.com/arviz-devs/arviz/issues/2476))
 
 ### Deprecation
 

arviz/data/inference_data.py

@@ -541,7 +541,9 @@ def to_datatree(self):
                 "xarray must be have DataTree in order to use InferenceData.to_datatree. "
                 "Update to xarray>=2024.11.0"
             ) from err
-        return DataTree.from_dict({group: ds for group, ds in self.items()})
+        dt = DataTree.from_dict({group: ds for group, ds in self.items()})
+        dt.attrs = self.attrs
+        return dt
 
     @staticmethod
     def from_datatree(datatree):
@@ -552,7 +554,8 @@ def from_datatree(datatree):
         datatree : DataTree
         """
         return InferenceData(
-            **{group: child.to_dataset() for group, child in datatree.children.items()}
+            attrs=datatree.attrs,
+            **{group: child.to_dataset() for group, child in datatree.children.items()},
         )
 
     def to_dict(self, groups=None, filter_groups=None):

arviz/tests/base_tests/test_data.py

@@ -1510,6 +1510,15 @@ def test_datatree(self):
             assert_identical(ds, idata_back[group])
         assert all(group in dt.children for group in idata.groups())
 
+    def test_datatree_attrs(self):
+        idata = load_arviz_data("centered_eight")
+        idata.attrs = {"not": "empty"}
+        assert idata.attrs
+        dt = idata.to_datatree()
+        idata_back = from_datatree(dt)
+        assert dt.attrs == idata.attrs
+        assert idata_back.attrs == idata.attrs
+
 
 class TestConversions:
     def test_id_conversion_idempotent(self):