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# A Monty Hall Paradox simulation program

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Today i created a simple program that simulates the Monty Hall paradox that i learned about here:

http://betterexplained.com/articles/understanding-the-monty-hall-problem/

It took me about two class periods (about an hour and a half) and helped me teach myself about using and defining functions. It was a cool project and didn't take very long to get working. I'd like to hear feedback on how i did as i am still a beginner! Here's the code:

[source lang="python"]# Monty Hall paradox game #
import pygame
import random

#variables
doors = [1, 2, 3]
x = random.randint(1, 3)

#function
def show():
print '================='
print '|',doors[0],'| |', doors[1],'| |',doors[2],'|'
print '================='

def reveal():
if x == 1:
doors[0] = 'C'
doors[1] = 'G'
doors[2] = 'G'
show()
elif x == 2:
doors[0] = 'G'
doors[1] = 'C'
doors[2] = 'G'
show()
elif x == 3:
doors[0] = 'G'
doors[1] = 'G'
doors[2] = 'C'
show()

def switch():
y = str(raw_input("Would you like to switch doors?"))
if y == 'yes':
new_pick = int(raw_input('Which door?'))
user_door = new_pick
reveal()
elif y == 'no':
reveal()

show()
user_door = int(raw_input('Pick a door!'))

#logic
if user_door == 1 and x == 3 and x != 2:
doors[1] = 'G'
show()
switch()

elif user_door == 1 and x == 2 and x != 3:
doors[2] = 'G'
show()
switch()

elif user_door == 2 and x == 3 and x != 1:
doors[0] = 'G'
show()
switch()

elif user_door == 2 and x == 1 and x != 3:
doors[2] = 'G'
show()
switch()

elif user_door == 3 and x == 1 and x != 2:
doors[1] = 'G'
show()
switch()

elif user_door == 3 and x == 2 and x != 1:
doors[0] = 'G'
show()
switch()
[/source]

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At first glance, this seems the most unusual thing in your code:

if user_door == 1 and x == 3 and x != 2:

What does the "x != 2" part do? If x is 3, of course it is not 2, you don't need to check that.

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I am not familar with python but instead of doing
show() and switch() in each elif statement you could just do it at the end a single time.

Unless python doesn't allow you to do that, in which case ignore me =)

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Yes, of course python allows that, and the suggestion is sound.

Also, what do you want to happen if I pick the correct door to begin with? Your program seems to just end in that case.

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I would recommend you to make the door numbering to start from zero. This way, you are mixing door numbers (starting from 1) and array indexes (starting from 0). That makes your program very confusing. Alvaro is right, too.

Also, you should move the hard work of choosing the third door to the computer. Your "wall of elif" can be written like
[source lang="python"]
if (user_door == x)
#participant has chosen the right door, so you can choose either one unselected
#let's go with the first door as default and the second as fallback
#note that's not entirely correct, we should use the random function, but serves the purpose
#if you have the time, try to replace it to use the random function
if (x != 0)
goat_door = 1;
else
goat_door = 2;
else
#one door has car in there and another is selected, the presenter opens the third
#we iterate over the doors and find that one
for test_door in [1,2,3]
if user_door != test_door and car_door != test_door
#we mark the door
goat_door = test_door
#and since it's marked, we don't need to iterate over another one
break
#KLUDGE: Going from one-based numbering to zero-based by subtracting one
doors[goat_door-1] = 'G'
show()
switch()
[/source]
It probably does the same thing, but the readability is greatly improved. That reduces chance of making an error. And that will save your 2 hours of "why is this not working right" someday.

P.S.: Use comments. Even a little bit really helps.

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I don't know Python at all; But I agree with ifthen:

P.S.: Use comments. Even a little bit really helps.

As a beginner: I comment to the point that I feel like I'm over-commenting; but I'm not. I can't count how many times I had to revisit a code file a week or month down the road and had to sit and stare at it wondering what the cob I was thinking when I wrote it. At the time, I probably thought it was a brilliant execution. But it isn't anymore. And my error is probably somewhere in those lines. Things would be a lot easier if I knew what I was thinking at 0300hrs that morning when I typed it... :/

So comment and comment some more. And Be descriptive.

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As a beginner: I comment to the point that I feel like I'm over-commenting; but I'm not. I can't count how many times I had to revisit a code file a week or month down the road and had to sit and stare at it wondering what the cob I was thinking when I wrote it. At the time, I probably thought it was a brilliant execution. But it isn't anymore. And my error is probably somewhere in those lines. Things would be a lot easier if I knew what I was thinking at 0300hrs that morning when I typed it... :/

I comment almost every single line in my code, and then filter out useless stuff later. I find it works well. I just don't get the hero coder attitude where people would write cryptic uncommented code that "just works". If you don't understand your own code, you probably should try to.

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ero coder attitude

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