Expose subentity types to python for easy creation of elements on entities. (#847)

* Expose subentity types to python for easy creation of elements on entites.

* Mypy fixes

Author: jorgensd

python/basix/_basixcpp.pyi

@@ -481,6 +481,8 @@ def restriction(arg0: PolysetType, arg1: CellType, arg2: CellType, /) -> Polyset
 
 def sobolev_space_intersection(arg0: SobolevSpace, arg1: SobolevSpace, /) -> SobolevSpace: ...
 
+def subentity_types(arg: CellType, /) -> list[list[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

@@ -15,11 +15,13 @@
 from basix._basixcpp import cell_facet_reference_volumes as _frv
 from basix._basixcpp import cell_volume as _v
 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 topology as _topology
 
 __all__ = [
     "sub_entity_connectivity",
+    "subentity_types",
     "volume",
     "facet_jacobians",
     "facet_normals",
@@ -143,3 +145,15 @@ def topology(celltype: CellType) -> list[list[list[int]]]:
         Vertex indices for each sub-entity of the cell.
     """
     return _topology(celltype)
+
+
+def subentity_types(celltype: CellType) -> list[list[CellType]]:
+    """Get the types of the subentities of a reference cell.
+
+    Args:
+        celltype: Cell type.
+
+    Returns:
+        Cell types for each sub-entity of the cell. Indices are (tdim, entity).
+    """
+    return _sut(celltype)

python/wrapper.cpp

@@ -432,7 +432,7 @@ NB_MODULE(_basixcpp, m)
           return as_nbarrayp(
               cell::sub_entity_geometry<double>(celltype, dim, index));
         });
-
+  m.def("subentity_types", &cell::subentity_types);
   m.def("sobolev_space_intersection", &sobolev::space_intersection);
 
   nb::enum_<lattice::type>(m, "LatticeType", nb::is_arithmetic(),