import bpy

import bpy_extras
import bpy_extras.mesh_utils
import bmesh


def get_new_linked_faces(faces, isl_2):
    new_linked_faces = []
    for face in faces:
        for v in face.verts:
            for face2 in v.link_faces:
                face_id = face2.index
                if face_id in isl_2 and face2 not in new_linked_faces:
                    new_linked_faces.append(face2)

    return new_linked_faces


def parse_sub_islands(isl, bm):
    isl_2 = isl.copy()
    sub_isls = []

    linked_faces = []

    first_face = bm.faces[isl_2[0]]
    linked_faces.append(isl_2[0])
    parse_faces = [first_face]
    isl_2.remove(isl_2[0])

    while parse_faces:

        new_faces = get_new_linked_faces(parse_faces, isl_2)
        if new_faces:
            for face in new_faces:
                linked_faces.append(face.index)
                isl_2.remove(face.index)
                parse_faces = new_faces

        elif isl_2:
            if linked_faces:
                sub_isls.append(linked_faces.copy())

            linked_faces = []

            parse_faces = [bm.faces[isl_2[0]]]
            linked_faces.append(isl_2[0])
            isl_2.remove(isl_2[0])

        else:
            if linked_faces:
                sub_isls.append(linked_faces.copy())

            linked_faces = None
            new_faces = None
            parse_faces = None
            break

    return sub_isls


if bpy.context.mode != 'OBJECT':
    bpy.ops.object.mode_set(mode='OBJECT', toggle=False)

active_obj = bpy.context.active_object
context_mode = active_obj.mode
bm = bmesh.new()
bm.from_mesh(active_obj.data)

bm.faces.ensure_lookup_table()
bm.verts.ensure_lookup_table()

islands = bpy_extras.mesh_utils.mesh_linked_uv_islands(active_obj.data)

# decompose to sub-islands
islands_dec = []
for isl_id, isl in enumerate(islands):
    if isl:
        if len(isl) > 1:
            new_isl = parse_sub_islands(isl, bm)
            islands_dec += new_isl
        else:
            islands_dec.append(isl.copy())


# Revert back
bpy.ops.object.mode_set(mode=context_mode, toggle=False)


print('Default mesh_linked_uv_islands ', islands)
print('Improved mesh_linked_uv_islands ', islands_dec)