prevent generator

tests/test_partitioning.py

@@ -135,7 +135,7 @@ def test_partition_roundtrip(self):
     def test_merge_partitions__errors(self):
         partitions = self.uds.ugrid.partition(n_part=2)
         with pytest.raises(TypeError, match="Expected UgridDataArray or UgridDataset"):
-            pt.merge_partitions(p.ugrid.obj for p in partitions)
+            pt.merge_partitions([p.ugrid.obj for p in partitions])
 
         grid1 = partitions[1].ugrid.grid
         partitions[1]["extra"] = (grid1.face_dimension, np.ones(grid1.n_face))

xugrid/ugrid/partitioning.py

@@ -328,10 +328,10 @@ def merge_partitions(partitions, merge_ugrid_chunks: bool = True):
     -------
     merged : UgridDataset
     """
+    if len(partitions) == 0:
+        raise ValueError("Cannot merge partitions: zero partitions provided.")
     types = {type(obj) for obj in partitions}
     msg = "Expected UgridDataArray or UgridDataset, received: {}"
-    if len(types) == 0:
-        raise ValueError("Cannot merge partitions: zero partitions provided.")
     if len(types) > 1:
         type_names = [t.__name__ for t in types]
         raise TypeError(msg.format(type_names))