Python3 script not producing expected results

Question

I have made a Python script to test the Monty Hall Problem My issue is that the code seems to output 30% wins and 60% losses when it should be doing the opposite.

from random import randint
wins = 0
losses = 0
for i in range(1000):
    correctDoor = randint(1, 3)
    guessDoor = randint(1, 3)
    while True:
        newGuessDoor = randint(1, 3)
        if newGuessDoor != guessDoor:
            break
        elif newGuessDoor == guessDoor:
            pass
    if newGuessDoor == correctDoor:
        wins = wins+1
    else:
        losses = losses+1
print('Wins = ' + str(wins) + '\nLosses = ' + str(losses) + '')

I feel like I'm missing something blatantly obvious. Any help will be appreciated.

@RadLexus Correct door, guessing door, new guessing door. I will update my code so it's easier to read. — Eli Richardson
– Eli Richardson, Commented Nov 3, 2016 at 20:29

Randy · Accepted Answer · 2016-11-03 20:42:02Z

4

This isn't actually implementing the Monty Hall problem correctly. When the initial guess is not correct, the other incorrect door is revealed before being given the offer to switch, and so it's a deterministic option. When the initial guess is correct, one of the other incorrect doors is revealed at random.

In your implementation, you're not being given any extra information after the initial guess -- you're just picking a 2nd door completely at random that isn't the same as your first door.

Here's an example of how you could implement the right method:

In [168]: from random import randint, choice
     ...: wins = 0
     ...: losses = 0
     ...: for i in range(1000):
     ...:     correctDoor = randint(1, 3)
     ...:     guessDoor = randint(1, 3)
     ...:     if guessDoor != correctDoor:
     ...:         newGuessDoor = correctDoor
     ...:     else:
     ...:         newGuessDoor = choice([i for i in [1,2,3] if i != guessDoor])
     ...:     if newGuessDoor == correctDoor:
     ...:         wins = wins+1
     ...:     else:
     ...:         losses = losses+1
     ...: print('Wins = ' + str(wins) + '\nLosses = ' + str(losses) + '')
     ...:
Wins = 653
Losses = 347

edited Nov 3, 2016 at 20:42

answered Nov 3, 2016 at 20:38

Randy

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1 Comment

Eli Richardson Over a year ago

Thanks. I made this in batch a long time ago and decided to recreate it in Python. I completely forgot to set a removal door.

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