fix: ensure radius values stored in AnnData.uns are writable

src/squidpy/gr/neighbors.py

@@ -88,7 +88,10 @@ def postprocessors(self) -> Sequence[GraphPostprocessor[GraphMatrixT]]:
 
     @abstractmethod
     def uns_params(self) -> dict[str, Any]:
-        """Parameters stored in :attr:`anndata.AnnData.uns` after graph construction."""
+        """Parameters stored in :attr:`anndata.AnnData.uns` after graph construction.
+
+        Values must be writable by :mod:`anndata`, e.g. a :class:`list`, not a :class:`tuple`.
+        """
 
     def combine(
         self,
@@ -234,7 +237,8 @@ def __init__(
             percentile=percentile,
             postprocessors=postprocessors,
         )
-        self.radius = radius
+        # Store intervals as a list: :mod:`anndata` cannot write tuples to ``uns``.
+        self.radius = list(radius) if isinstance(radius, tuple) else radius
 
     def uns_params(self) -> dict[str, Any]:
         return {
@@ -303,7 +307,8 @@ def __init__(
             percentile=percentile,
             postprocessors=postprocessors,
         )
-        self.radius = radius
+        # Store intervals as a list: :mod:`anndata` cannot write tuples to ``uns``.
+        self.radius = list(radius) if isinstance(radius, tuple) else radius
 
     def uns_params(self) -> dict[str, Any]:
         return {

tests/graph/test_spatial_neighbors.py

@@ -12,7 +12,13 @@
 
 from squidpy._constants._constants import Transform
 from squidpy._constants._pkg_constants import Key
-from squidpy.gr import mask_graph, spatial_neighbors, spatial_neighbors_from_builder
+from squidpy.gr import (
+    mask_graph,
+    spatial_neighbors,
+    spatial_neighbors_delaunay,
+    spatial_neighbors_from_builder,
+    spatial_neighbors_radius,
+)
 from squidpy.gr.neighbors import (
     DelaunayBuilder,
     GridBuilder,
@@ -277,6 +283,23 @@ def test_delaunay_builder_scalar_radius_equals_zero_max_tuple(self, non_visium_a
         np.testing.assert_array_equal(scalar.connectivities.toarray(), interval.connectivities.toarray())
         np.testing.assert_allclose(scalar.distances.toarray(), interval.distances.toarray())
 
+    @pytest.mark.parametrize(
+        ("func", "radius", "expected"),
+        [
+            (spatial_neighbors_radius, 5.0, 5.0),
+            (spatial_neighbors_radius, (2.0, 4.0), [2.0, 4.0]),
+            (spatial_neighbors_delaunay, (2.0, 4.0), [2.0, 4.0]),
+            (spatial_neighbors_delaunay, 5.0, [0.0, 5.0]),
+        ],
+        ids=["radius_scalar", "radius_interval", "delaunay_interval", "delaunay_scalar"],
+    )
+    def test_radius_stored_in_uns_is_writable(self, non_visium_adata: AnnData, tmp_path, func, radius, expected):
+        func(non_visium_adata, radius=radius)
+
+        # an interval radius is stored as a list: `anndata` cannot write tuples
+        assert non_visium_adata.uns[Key.uns.spatial_neighs()]["params"]["radius"] == expected
+        non_visium_adata.write_h5ad(tmp_path / "adata.h5ad")
+
     def test_delaunay_mode_warns_on_n_neighs(self, non_visium_adata: AnnData):
         with pytest.warns(FutureWarning, match=r"Parameter `n_neighs` is ignored when `delaunay=True`"):
             spatial_neighbors(non_visium_adata, coord_type="generic", delaunay=True, n_neighs=3, copy=True)