Maya get faces of mesh per island or poly shell

maya_get_mesh_shells.py

from maya import cmds

def get_shells(mesh, as_selection_string=True):
    """Return faces per shell of mesh"""
    
    num_shells = cmds.polyEvaluate(mesh, shell=True)
    num_faces = cmds.polyEvaluate(mesh, face=True)
    
    unprocessed = set(range(num_faces))
    
    shells = []
    while unprocessed:
        face_index = next(iter(unprocessed))
        shell_faces = cmds.polySelect(mesh, extendToShell=face_index, noSelection=True)
        
        if as_selection_string:
            yield ["{}.f[{}]".format(mesh, face_index) for face_index in shell_faces]
        else:
            yield shell_faces
        
        unprocessed.difference_update(shell_faces)
        
for node in cmds.ls(sl=1, objectsOnly=True):
    for faces in get_shells(node):
        print(faces)