qgis - Label only selected features with PAL PyQgis using an expression

I'm trying to label only selected features with an expression using PyQgis and the PAL functions, but I don't find any example and the API don't help me a lot (or I don't found it). My Qgis version is 2.14

This is an extract of my code:

from PyQt4.QtGui import QColor
layer = iface.activeLayer()
palyr = QgsPalLayerSettings()
palyr.readFromLayer(layer)

palyr.enabled = True 
palyr.bufferDraw= True
palyr.bufferColor= QColor("white")
palyr.bufferSize = 1
palyr.scaleVisibility = True
palyr.scaleMax=2000
palyr.isExpression = True
# code is a fieldname. Only show the last 3 letters
palyr.fieldName = 'right( code ,3 )'   
palyr.size = 20

# next 2 lines is for change placement 
palyr.placement= QgsPalLayerSettings.OverPoint 
palyr.setDataDefinedProperty(QgsPalLayerSettings.Size,True,True,'8','') 

# I want to set this expression for label only selected features:  "code not like '%000'" 
# MISSING CODE FOR SET DEFINED LABEL USING EXPRESSION 

palyr.textColor = QColor("red")
palyr.drawLabels = True
palyr.writeToLayer(layer)

iface.mapCanvas().refresh()

I can run this code without errors, but I don't know how to set expression for defined data features.