blender/scripts/templates_py/ui_pie_menu.py

import bpy
from bpy.types import Menu

# spawn an edit mode selection pie (run while object is in edit mode to get a valid output)


class VIEW3D_MT_PIE_template(Menu):
    # label is displayed at the center of the pie menu.
    bl_label = "Select Mode"

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

        pie = layout.menu_pie()
        # operator_enum will just spread all available options
        # for the type enum of the operator on the pie
        pie.operator_enum("mesh.select_mode", "type")


def register():
    bpy.utils.register_class(VIEW3D_MT_PIE_template)


def unregister():
    bpy.utils.unregister_class(VIEW3D_MT_PIE_template)


if __name__ == "__main__":
    register()

    bpy.ops.wm.call_menu_pie(name="VIEW3D_MT_PIE_template")