Python - Condicional en un periodo de tiempo

import datetime

def lee_x():

    ###### aqui leera su valor actual. Se me ocurre devolver 1

    return 2

def lee_y():

    ###### aqui lera su valor actual

    return 2

comienzo = datetime.datetime.now()

final = comienzo + datetime.timedelta(seconds=5)

coinciden = None

while datetime.datetime.now() < final:

    if coinciden != True and lee_x() == lee_y():

        print 'Coinciden'

        coinciden = True

    elif coinciden != False and lee_x() != lee_y():

        print 'Diferentes'

        coinciden = False