monty_hall.py

#!/usr/bin/env python3

from random import randrange, shuffle, choice
from collections import Counter


class Judge(object):
    def __init__(self):
        self.doors = ['goat', 'goat', 'CAR']
        shuffle(self.doors)                 # move the prize into a random door

    def open_wrong_door(self, select):
        avail = [i for i, d in enumerate(self.doors) if d == 'goat']    # don't open the correct door
        if select in avail:
            avail.remove(select)            # don't open the door that player currently select
        return choice(avail)



class Player(object):
    def __init__(self):
        self.doors = ['?', '?', '?']        # player did not know which door has the prize
        self.select = None

    def select_available_door(self):
        avail = [i for i, d in enumerate(self.doors) if d == '?']   # only guess unopened door
        self.select = choice(avail)         # random a door that may have prize

    def change_door(self):
        avail = [i for i, d in enumerate(self.doors) if d == '?']   # only guess unopened door
        avail.remove(self.select)           # don't select the selected door again
        self.select = choice(avail)         # practically it is the only door left

    def acknowledge_wrong_door(self, judge):
        index = judge.open_wrong_door(self.select)
        self.doors[index] = 'goat'

    def confirm_selected_door(self, judge):
        return judge.doors[self.select]



def strategy_stay():
    judge = Judge()
    player = Player()
    player.select_available_door()
    player.acknowledge_wrong_door(judge)
    return player.confirm_selected_door(judge)


def strategy_rerandom():
    judge = Judge()
    player = Player()
    player.select_available_door()
    player.acknowledge_wrong_door(judge)
    player.select_available_door()
    return player.confirm_selected_door(judge)



def strategy_change():
    judge = Judge()
    player = Player()
    player.select_available_door()
    player.acknowledge_wrong_door(judge)
    player.change_door()
    return player.confirm_selected_door(judge)



n = 100000
print('Stay on the first door')
print('======================')
for k, v in sorted(Counter(strategy_stay() for _ in range(n)).items()):
    print(f'{k:4} {100*v/n:6.2f}%')
print()
print('Random the door again')
print('=====================')
for k, v in sorted(Counter(strategy_rerandom() for _ in range(n)).items()):
    print(f'{k:4} {100*v/n:6.2f}%')
print()
print('Change the door')
print('===============')
for k, v in sorted(Counter(strategy_change() for _ in range(n)).items()):
    print(f'{k:4} {100*v/n:6.2f}%')
print()