Batch Delete Vertex Groups script改の2.9x改造

bl_info = {
    "name": "Remove Unused Vertex Groups",
    "author": "ave, CoDEmanX, あんじっぷ",
    "version": (1, 0),
    #"blender": (2, 70, 0),
    "blender": (2, 80, 0),
    "location": "Properties Editor > Object data > Vertex Groups > Specials menu",
    "description": "Delete Vertex Groups with no assigned weight of active object",
    "warning": "",
    "wiki_url": "",
    "category": "Mesh"}

# taken from here:
# https://blenderartists.org/t/batch-delete-vertex-groups-script/449881/5


import bpy
from bpy.types import Operator


class OBJECT_OT_remove_unused_vertex_group(Operator):
    bl_idname = "object.remove_unused_vertex_group"
    bl_label = "Remove unused vertex groups"
    bl_options = {'REGISTER', 'UNDO'}

    @classmethod
    def poll(cls, context):
        return (context.object is not None and
                context.object.type == 'MESH')

    def execute(self, context):

        suffix_map = {".L": ".R", ".l": ".r", "_L": "_R", "_l": "_r",
                      "-L": "-R", "-l": "-r",
                      ".R": ".L", ".r": ".l", "_R": "_L", "_r": "_l",
                      "-R": "-L", "-r": "-l"}

        ob = context.object
        ob.update_from_editmode()

        has_mirror = len([x for x in ob.modifiers if x.type == 'MIRROR']) > 0
        suffix = suffix_map.keys()
        vgroups = ob.vertex_groups
        vgroup_used = {i: False for i, k in enumerate(vgroups)}

        for v in ob.data.vertices:
            for g in v.groups:
                if g.weight > 0.0:
                    vgroup_used[g.group] = True
                    if has_mirror:
                        name = vgroups[g.group].name
                        if name[-2:] in suffix:
                            i = vgroups.find(name[:-2] + suffix_map[name[-2:]])
                            vgroup_used[i] = True

        for i, used in sorted(vgroup_used.items(), reverse=True):
            if not used:
                vgroups.remove(vgroups[i])

        return {'FINISHED'}


def menu_fn(self, context):
    self.layout.operator(
        OBJECT_OT_remove_unused_vertex_group.bl_idname,
        icon='X'
    )


def register():
    from bpy.utils import register_class
    register_class(OBJECT_OT_remove_unused_vertex_group)
    bpy.types.MESH_MT_vertex_group_context_menu.prepend(menu_fn)


def unregister():
    from bpy.utils import unregister_class
    unregister_class(OBJECT_OT_remove_unused_vertex_group)
    bpy.types.MESH_MT_vertex_group_context_menu.remove(menu_fn)

if __name__ == "__main__":
    register()