How to create facemaps from a set of known vert groups

gistfile1.txt

def create_facemaps(self, object):
    me = object.data
    bm = bmesh.new()
    bm.from_mesh(me)
    bm.select_mode = {'VERT', 'EDGE', 'FACE'}
    bm.verts.ensure_lookup_table()
    bm.faces.ensure_lookup_table()
    fm = bm.faces.layers.face_map.verify()

    group_names = ['InnerShell', 'OuterShell', 'UpperBearingEdge', 'LowerBearingEdge']
    for grp_name in group_names:
        new_fm = object.face_maps.new(name=grp_name)
        
        vert_idxs = self.shell_verts[grp_name]
        for idx in vert_idxs:
            vert = bm.verts[idx]
            vert.select = True
        
        bm.select_flush_mode()
        faces = [face for face in bm.faces if face.select]
        
        for face in faces:
            face[fm] = new_fm.index


        for vert in bm.verts:
            vert.select = False

    me.update(calc_edges=True, calc_edges_loose=True)
    bm.to_mesh(me)
    bm.free()
    return