How add pie menu for scene enum property

I have defined a scene prop like this:

    bpy.types.Scene.my_orientation = bpy.props.EnumProperty(items = (('1',"X+","Change the slope orientation"),
                                ('2',"Y+","Change the slope orientation"),
                                ('3',"X-","Change the slope orientation"),
                                ('4',"Y-","Change the slope orientation")),
                                name="Orientation",
                                description="Orientation")



Then, I use the prop in a panel with this code:

row.prop(scene,"my_orientation")

I have done something like this for pie menu using the template provided by Blender:

import bpy
from bpy.types import Menu, Operator
from bpy.props import EnumProperty


class VIEW3D_PIE_template(Menu):
    # label is displayed at the center of the pie menu.
    bl_label = "my pie"


    def draw(self, context):
        layout = self.layout


        pie = layout.menu_pie()
        pie.operator_enum("my_orientation")  # <<<< This line is not working, why?????


def register():
    bpy.utils.register_class(VIEW3D_PIE_template)

def unregister():
    bpy.utils.unregister_class(VIEW3D_PIE_template)

if __name__ == "__main__":
    register()

    bpy.ops.wm.call_menu_pie(name="VIEW3D_PIE_template")



What is wrong? I have no options in the pie menu



def draw(self, context):
     #...
     pie.prop(context.scene, "my_orientation", expand=True)
     #...

Thanks Stan,

I yesterday tested several options, but I didn’t think to use context.scene as first parameter…so easy!