montyhall.py

from __future__ import print_function

from collections import namedtuple
import random

# Create an easy-to-return and easy-to-inspect data
# structure for Game results.
Results = namedtuple('Results', ['won', 'switched'])


class Door(object):
    prize = False
    opened = False


class Game(object):
    chosen_door = None
    switched_doors = False

    def __init__(self):
        self.doors = [
            Door(),
            Door(),
            Door()
        ]
        # Pick a random door and give it a prize
        random.choice(self.doors).prize = True

    def pick_door(self):
        self.chosen_door = random.choice(self.doors)

    def open_false_door(self):
        # Get the non-chosen doors
        available_doors = [door for door in self.doors
                           if door is not self.chosen_door]
        for door in available_doors:
            if not door.prize:
                # Open the first prizeless door
                door.opened = True
                break

    def switch_doors(self):
        available_door = [door for door in self.doors
                          if door is not self.chosen_door
                          and not door.opened][0]
        if random.randint(0, 1):
            # Randomly decide to switch doors
            self.switched_doors = True
            self.chosen_door = available_door

    @classmethod
    def play(cls):
        game = cls()
        game.pick_door()
        game.open_false_door()
        game.switch_doors()

        return Results(game.chosen_door.prize, game.switched_doors)


# Play 1000 runs of the game to get significant numbers
games = [Game.play() for _ in range(1000)]

# Games where the player switched doors and won the prize
won_switched = list(filter(lambda g: g.won and g.switched, games))

# Games where the player did *not* switch doors and won the prize
won_original = list(filter(lambda g: g.won and not g.switched, games))

# Games where the player did *not* switch doors and lost
lost_original = list(filter(lambda g: not g.won and not g.switched, games))

# Games where the player switched doors and lost
lost_switched = list(filter(lambda g: not g.won and g.switched, games))

print("Won and switched:", len(won_switched))
print("Won and didn't switch:", len(won_original))
print("Lost and switched:", len(lost_switched))
print("Lost and didn't switch:", len(lost_original))