Dinamic Cam with python for BGE..help

how i say in the title of this thread I want to make a dinamic cam with a scripto on python for BGE, in which the camera can do to increase or decrease the length of lens, eg 30mm to 55mm but progressively without glitchs.
Any sugestion about it?

import GameLogic as gl
import GameKeys

scene = gl.getCurrentScene()
objects = scene.objects

camera = objects[‘OBCamera’]

#print camera

print dir(camera)
camera.lens = 10

that is part of my first try
i need the camera change but secuencially

A zoom in / zoom out script for BGE suggestions ?