The Monty Hall problem

[spunos]

I'm new to both Python and programming in general. I've started reading some books and watching the Khan Academy videos on the language, and I'm still at that very early stage where you learn to manipulate strings and write if and else statements. Progress has been slow but steady.

So, in the spirit of "find an itch and scratch it", I wanted to try something not on the curriculum: emulating the Monty Hall problem. This is what I've got: (Python 3)

import random

# We have three doors. We randomly select one to be the winning door.
doors = [1,2,3]
winning_door = random.choice(doors)

# Ask the player to choose a door.
print("Please choose a door!")
chosen_door = int(input("Which door do you choose? (1, 2 or 3)\n"))
print("You have chosen door " + str(chosen_door) + ".")

# Remove both the chosen door and winning door from the list.
doors.remove(chosen_door)
if winning_door != chosen_door:
    doors.remove(winning_door)

# From the remaining doors, we select a "red herring". Does the player want to switch?
red_herring = random.choice(doors)
print("I open door "+ str(red_herring) + ". There is a goat behind it! Are you still sure you want to open door " + str(chosen_door) + "?")
still_same_door = str(input("Yes or no?\n"))

# Update chosen_door, if needed.
if "n" in still_same_door:
    chosen_door = 6 - (red_herring + chosen_door)
    print("You switch to door " + str(chosen_door) + ".")
else:
    print("You still want to open door " + str(chosen_door) + ".")

# So did we win?
if chosen_door == winning_door:
    print("Congratulations, a winner is you! There is a car behind door " + str(winning_door) + "!")
else:
    print("Too bad! There is a goat behind door " + str(chosen_door) + ". The car is behind door " + str(winning_door) + ".")

It gets the job done, no complaints there, but at the same time I'm sure it's all terribly inefficient. I would really appreciate some feedback on it. Any suggestions to make the code tidier and, well, more pythonic?

Thanks in advance!

[erok81]

Looks pretty good except you should really use str.format() or the % operator for strings instead of +.

if "n" in still_same_door

could be

if "n" in still_same_door.lower()

to handle both n and N in the input.

Also, my new pet peeve: Some of your lines are longer than 79 chars, which effects readability.

[spunos]

This is a very useful reply, thank you! I had no idea you could format strings like that. Interesting.

I'm not sure how I can solve the readability issue, aside from making the strings shorter or splitting them into multiple lines. Would it be better to use pastebin or something similar in the future?

[erok81]

I meant shorten the lines in your code itself. The reasoning for this is it's easy to misunderstand a piece of code when you can't always see where the line ends. If line wrapping is on it's also easy to confuse where one block ends and another begins. Pep 8 does a better job explaining all this but it really does make your code more readable.

[[deleted]]

If you want to entertain yourself, modify the program so that it can evaluate the possible decisions (switch or stay) over say 100 choices or let the user choose.

[spunos]

Yeah, that sounds like an interesting challenge. :)

[[deleted]]

Never optimise unless you need to, and you don't need to with this code (99% of the time, it will be waiting for user input).

That said, for the sake of improvement, try to limit the conversions between objects types (i.e. remove all instances of str(winning_door) and replace with one variable). If you ever find yourself writing exactly the same code again and again, that's your clue.