[Blender Add-on] Switch to Weight Paint and select Armature

WeightPaintSelectArmature.py

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import bpy

bl_info = {
    "name": "Switch to Weight Paint and select Armature",
    "author": "ZipFile",
    "blender": (2, 80, 0),
    "version": (0, 0, 1),
    "description": "Switch to Weight Paint Mode and select associated Armature",
    "category": "Object",
    "location": "Context menu",
}


def find_armature(obj):
    for modifier in obj.modifiers:
        if modifier.type == "ARMATURE" and modifier.object:
            return modifier.object
    return None


def is_mesh(obj):
    return obj is not None and obj.type == "MESH"


class WeightPaintSelectArmature(bpy.types.Operator):
    """Switch to Weight Paint and select Armature"""

    bl_idname = "object.weight_paint_select_armature"
    bl_label = "Weight Paint and Select Armature"
    bl_options = {"REGISTER", "UNDO"}

    @classmethod
    def poll(cls, context):
        return is_mesh(context.active_object)

    def execute(self, context):
        mesh = context.active_object
        armature = find_armature(mesh)

        if armature is None:
            self.report({"ERROR"}, "No armature connected to the mesh.")

            return {"CANCELLED"}

        bpy.ops.object.select_all(action="DESELECT")

        bpy.context.view_layer.objects.active = armature

        armature.select_set(True)

        bpy.context.view_layer.objects.active = mesh

        bpy.ops.object.mode_set(mode="WEIGHT_PAINT")

        return {"FINISHED"}


def menu_func(self, context):
    self.layout.operator(WeightPaintSelectArmature.bl_idname)


def register():
    bpy.utils.register_class(WeightPaintSelectArmature)
    bpy.types.VIEW3D_MT_object_context_menu.append(menu_func)


def unregister():
    bpy.types.VIEW3D_MT_object_context_menu.remove(menu_func)
    bpy.utils.unregister_class(WeightPaintSelectArmature)


if __name__ == "__main__":
    register()