while again:
print" Pick a dice: "
print"4, 6, 12"
userinput = input("Pick a dice: ")
if userinput == 4:
randomnumber = random.randint(1,4)
print randomnumber
if userinput == 6:
randomnumber = random.randint(1,6)
print randomnumber
if userinput == 12:
randomnumber = random.randint(1,12)
print randomnumber