How to make this code pick a random number each call Python?

#randomly picks a monster for a random encounter        
class RanMob:
    #randint(1,2)
    roll=Dice.die(2)
    if roll ==1:
        mob=Goblin(Goblin.name,Goblin.hp,Goblin.thaco,Goblin.ac,Goblin.inventory)
    if roll ==2:
        mob=Orc(Orc.name,Orc.hp,Orc.thaco,Orc.ac,Orc.inventory)

while True:
    #pick a new random monster
    RanMob()
    #print the name of the random monster
    print(RanMob.mob.name)

When I run this code the RanMob class picks a new random number the first time through and then never picks a new number. How do I get it to pick a new mob each time I call RanMob in the main game loop?