RF: return CIFTI_MODEL_TYPE to distinguish surface and voxels

Author: MichielCottaar

nibabel/cifti2/cifti2_axes.py

@@ -670,13 +670,15 @@ def get_element(self, index):
         Returns
         -------
         tuple with 3 elements
-        - boolean, which is True if it is a surface element
+        - str, 'CIFTI_MODEL_TYPE_SURFACE' for vertex or 'CIFTI_MODEL_TYPE_VOXELS' for voxel
         - vertex index if it is a surface element, otherwise array with 3 voxel indices
         - structure.BrainStructure object describing the brain structure the element was taken from
         """
-        is_surface = self.name[index] in self.nvertices.keys()
-        struct = self.vertex if is_surface else self.voxel
-        return is_surface, struct[index], self.name[index]
+        element_type = 'CIFTI_MODEL_TYPE_' + (
+            'SURFACE' if self.name[index] in self.nvertices.keys() else 'VOXELS'
+        )
+        struct = self.vertex if 'SURFACE' in element_type else self.voxel
+        return element_type, struct[index], self.name[index]
 
 
 class Parcels(Axis):

nibabel/cifti2/tests/test_axes.py

@@ -107,7 +107,7 @@ def test_brain_models():
     assert len(bml[0]) == 3
     assert (bml[0].vertex == -1).all()
     assert (bml[0].voxel == [[0, 1, 2], [0, 4, 0], [0, 4, 2]]).all()
-    assert bml[0][1][0] == False
+    assert bml[0][1][0] == 'CIFTI_MODEL_TYPE_VOXELS'
     assert (bml[0][1][1] == [0, 4, 0]).all()
     assert bml[0][1][2] == axes.BrainModel.to_cifti_brain_structure_name('thalamus_right')
     assert len(bml[1]) == 4
@@ -116,11 +116,11 @@ def test_brain_models():
     assert len(bml[2]) == 3
     assert (bml[2].voxel == -1).all()
     assert (bml[2].vertex == [0, 5, 10]).all()
-    assert bml[2][1] == (True, 5, 'CIFTI_STRUCTURE_CORTEX_LEFT')
+    assert bml[2][1] == ('CIFTI_MODEL_TYPE_SURFACE', 5, 'CIFTI_STRUCTURE_CORTEX_LEFT')
     assert len(bml[3]) == 4
     assert (bml[3].voxel == -1).all()
     assert (bml[3].vertex == [0, 5, 10, 13]).all()
-    assert bml[4][1] == (True, 9, 'CIFTI_STRUCTURE_CORTEX_RIGHT')
+    assert bml[4][1] == ('CIFTI_MODEL_TYPE_SURFACE', 9, 'CIFTI_STRUCTURE_CORTEX_RIGHT')
     assert len(bml[4]) == 3
     assert (bml[4].voxel == -1).all()
     assert (bml[4].vertex == [2, 9, 14]).all()