Monte Carlo Simulation for the Monty Hall Problem

import random, sys

TRIALS = 1000    # trials per strategy (swap and don't swap)
DOORS = 3       # number of doors in the experiment

def test_swap(doors):
  door_list = [0]*(doors - 1) + [1]
  random.shuffle(door_list)
  rand_doors = dict(zip(range(doors), door_list))    # create the doors
  door_num = random.choice(list(rand_doors.keys()))    # choose a door
  
  if rand_doors[door_num]:    # if you chose the prize door
    # You lose the prize because the host eliminates all but one of the
    # goat doors, and you swap from the prize door to that goat door
    return False
  elif not rand_doors[door_num]:    # if you chose a goat door
    # You win the prize because the host eliminates all of the other
    # goat doors, and you swap from your goat door to the prize door
    return True

def test_no_swap(doors):
  door_list = [0]*(doors - 1) + [1]
  random.shuffle(door_list)
  rand_doors = dict(zip(range(doors), door_list))    # create the doors
  door_num = random.choice(list(rand_doors.keys()))    # choose a door
  
  if rand_doors[door_num]:    # if you chose the prize door
    # You win the prize because the host eliminates all but one
    # of the other goat doors, but you keep the prize door
    return True
  elif not rand_doors[door_num]:    # if you chose a goat door
    # You lose the prize because the host eliminates all the
    # other goat doors, but you keep your original goat door
    return False

##################################################################
###                         Main Script                        ###
##################################################################

if sys.version_info[0] == 2: print 'Running ...',
elif sys.version_info[0] == 3: exec("print('Running...', end=' ')")

swap_wins, no_swap_wins = 0, 0

for i in range(TRIALS):
  if test_swap(DOORS):
    swap_wins += 1
  if test_no_swap(DOORS):
    no_swap_wins += 1

print('Done')
print('Not swapping doors won you {0} prizes out of {1} ({2}%)'.format(no_swap_wins, TRIALS, str(float(no_swap_wins) / TRIALS * 100)[:5]))
print('Swapping doors won you {0} prizes out of {1} ({2}%)'.format(swap_wins, TRIALS, str(float(swap_wins) / TRIALS * 100)[:5]))

Python Fiddle

Python Cloud IDE