wrap sub_entity_type (#888)

* wrap sub_entity_type

* update pyi

* the other pyi too

* ,

basix/_basixcpp.pyi

@@ -459,6 +459,8 @@ def restriction(arg0: PolysetType, arg1: CellType, arg2: CellType, /) -> Polyset
 
 def sobolev_space_intersection(arg0: SobolevSpace, arg1: SobolevSpace, /) -> SobolevSpace: ...
 
+def sub_entity_type(arg: CellType, dim: int, index: int, /) -> CellType: ...
+
 def sub_entity_connectivity(arg: CellType, /) -> list[list[list[list[int]]]]: ...
 
 def sub_entity_geometry(arg0: CellType, arg1: int, arg2: int, /) -> Annotated[ArrayLike, dict(dtype='float64', )]: ...

python/basix/_basixcpp.pyi

@@ -483,6 +483,8 @@ def sobolev_space_intersection(arg0: SobolevSpace, arg1: SobolevSpace, /) -> Sob
 
 def subentity_types(arg: CellType, /) -> list[list[CellType]]: ...
 
+def sub_entity_type(arg: CellType, dim: int, index: int, /) -> CellType: ...
+
 def sub_entity_connectivity(arg: CellType, /) -> list[list[list[list[int]]]]: ...
 
 def sub_entity_geometry(arg0: CellType, arg1: int, arg2: int, /) -> Annotated[ArrayLike, dict(dtype='float64', )]: ...

python/basix/cell.py

@@ -17,6 +17,7 @@
 from basix._basixcpp import geometry as _geometry
 from basix._basixcpp import subentity_types as _sut
 from basix._basixcpp import sub_entity_connectivity as _sec
+from basix._basixcpp import sub_entity_type as _set
 from basix._basixcpp import topology as _topology
 
 __all__ = [
@@ -31,6 +32,20 @@
 ]
 
 
+def sub_entity_type(celltype: CellType, dim: int, index: int) -> CellType:
+    """Cell type of a sub-entity.
+
+    Args:
+        celltype: cell type.
+        dim: dimension of the sub-entity.
+        index: index of the sub-entity
+
+    Returns:
+        The cell type of the sub-entity.
+    """
+    return _set(celltype, dim, index)
+
+
 def sub_entity_connectivity(celltype: CellType) -> list[list[list[list[int]]]]:
     """Numbers of entities connected to each sub-entity of the cell.
 

python/wrapper.cpp

@@ -425,6 +425,8 @@ NB_MODULE(_basixcpp, m)
   m.def("topology", &cell::topology);
   m.def("geometry", [](cell::type celltype)
         { return as_nbarrayp(cell::geometry<double>(celltype)); });
+  m.def("sub_entity_type", [](cell::type celltype, int dim, int index)
+        { return cell::sub_entity_type(celltype, dim, index); });
   m.def("sub_entity_connectivity", &cell::sub_entity_connectivity);
   m.def("sub_entity_geometry",
         [](cell::type celltype, int dim, int index)

test/test_cell.py

@@ -78,3 +78,14 @@ def test_sub_entity_connectivity(cell):
                     else:
                         for i in topology[dim][n]:
                             assert i in topology[dim2][n2]
+
+
+def test_sub_entity_type():
+    cell_type = basix.CellType.tetrahedron
+    for i in range(4):
+        assert basix.cell.sub_entity_type(cell_type, 0, i) == basix.CellType.point
+    for i in range(6):
+        assert basix.cell.sub_entity_type(cell_type, 1, i) == basix.CellType.interval
+    for i in range(4):
+        assert basix.cell.sub_entity_type(cell_type, 2, i) == basix.CellType.triangle
+    assert basix.cell.sub_entity_type(cell_type, 3, 0) == basix.CellType.tetrahedron