How change the Pie Menu Radius with python? I want to change the pie menu radius using python, 
after some search I can access to that propertie using:

bpy.types.UserPreferencesView.bl_rna.properties['pie_menu_radius'].


but I can't change it

some help please! :D
And similar can be done for all other items on the User-Preferences -> Interface tab. (Warning doesn't update the visible value on the UI until you move your mouse, or trigger ui redraw some other way)

import bpy
prefs = bpy.context.user_preferences
prefs.view.pie_menu_radius = 80