import random

emptyList = []

while True:

letterList = ['A','B','C','D','E','F','G','H','I','J','K','L','M','N']

idx = random.randint(0,len(letterList)-1)

letter = letterList[idx]

emptyList.append(letter)

letterList.pop(idx)

if len(emptyList) == 3:

break

print(emptyList)