Simple monty hall problem simulation

monty.py

import random

trials = 100
stay = []
switch = []
for t in range(trials):
  possibilities = [1,2,3]
  ans = random.choice(possibilities)
  stay_ans = random.choice(possibilities)
  stay.append(stay_ans == ans) #either true or false

  possibilities = set(possibilities)
  discard = possibilities.difference(set((stay_ans, ans))).pop()
  switch_ans = possibilities.difference(set((stay_ans, discard))).pop()
  switch.append(switch_ans == ans)


stay_win = sum(stay)*100/len(stay)
print("Stay win %d%%" % stay_win)
switch_win = sum(switch)*100/len(switch)
print("Switch win %d%%" % switch_win)