Pie menu with custom icons

__init__.py

import os

import bpy
import bpy.utils.previews
from bpy.types import Menu, Operator
from bpy.props import StringProperty

bl_info = {
    "name": "ViewPort Navigator Pie Menu (Demo - with custom icons)",
    "author": "Dealga McArdle",
    "version": (0, 0, 1),
    "blender": (2, 7, 5),
    "location": "Viewport",
    "description": "Adds pie menu with viewport navigation options.",
    "wiki_url": "",
    "tracker_url": "",
    "category": "3D View"}


operator_behaviours = ['anchor', 'pinch', 'rotator']
preview_collections = {}


class VIEW3D_PM_NAV_ops(Operator):
    bl_idname = "view3d.pie_menu_navigator"
    bl_label = "Quickly Navigate 3dview"

    b_type = StringProperty()

    def execute(self, context):
        if not self.b_type:
            return {'CANCELLED'}

        print('action path:', self.b_type)
        return {'FINISHED'}


class VIEW3D_MT_PIE_Menu_Nav(Menu):
    bl_label = "Navigate"
    bl_idname = "view3d.pie_menu_base"

    def draw(self, context):
        pcoll = preview_collections["nav_main"]
        view_ops = "view3d.pie_menu_navigator"

        pie = self.layout.menu_pie()
        for behaviour in operator_behaviours:
            icon = pcoll[behaviour]
            pie.operator(view_ops, text=behaviour, icon_value=icon.icon_id).b_type = behaviour


def register():
    import bpy.utils.previews
    pcoll = bpy.utils.previews.new()

    icons_dir = os.path.join(os.path.dirname(__file__), "icons")

    for img in operator_behaviours:
        full_img_name = (img + ".png")
        img_path = os.path.join(icons_dir, full_img_name)
        pcoll.load(img, img_path, 'IMAGE')

    preview_collections["nav_main"] = pcoll

    bpy.utils.register_class(VIEW3D_PM_NAV_ops)
    bpy.utils.register_class(VIEW3D_MT_PIE_Menu_Nav)


def unregister():

    for pcoll in preview_collections.values():
        bpy.utils.previews.remove(pcoll)
    preview_collections.clear()

    bpy.utils.unregister_class(VIEW3D_MT_PIE_Menu_Nav)
    bpy.utils.unregister_class(VIEW3D_PM_NAV_ops)


if __name__ == "__main__":
    register()