Help with Python

[pith]

Hello, I need help with editing this program:

#!/usr/bin/env python
"""
Monte Carlo simulation for the Monty Hall Problem:
http://en.wikipedia.org/wiki/Monty_Hall_problem.
"""
import sys
from random import randrange, shuffle, choice

DOORS = ['car', 'goat', 'goat']

def pick_door():
    """Return a number representing the player's first choice."""
    return randrange(3)

def reveal_door(pick):
    """Return the index of the door opened by the host.
    This cannot be a door hiding a car or the player's chosen door.
    """
    all_doors = set([0, 1, 2])
    unavailable_doors = set([DOORS.index('car'), pick])
    available_doors = list(all_doors - unavailable_doors)
    return choice(available_doors)

def staying_wins(pick):
    """Return True if the player won by staying
    with their first choice, False otherwise.
    """
    return won(pick)

def switching_wins(pick, open_door):
    """Return True if the player won by switching,
    False otherwise.
    """
    other_doors = set([pick, open_door])
    switched_pick = (set([0, 1, 2]) - other_doors).pop()
    return won(switched_pick)

def won(pick):
    """Return True if the player's final pick hides a car,
    False otherwise.
    """
    return (DOORS[pick] == 'car')

def main(iterations=1000000):
    """Run the main simulation as many
    times as specified by the function argument.
    """
    shuffle(DOORS)

    switching = 0
    staying = 0

    for dummy in xrange(iterations):
        picked = pick_door()
        revealed = reveal_door(picked)
        if staying_wins(picked):
            staying += 1
        if switching_wins(picked, revealed):
            switching += 1

    staying_rate = (float(staying) / iterations) * 100
    switching_rate = (float(switching) / iterations) * 100

    print "Staying: %f%%" % staying_rate
    print "Switching: %f%%" % switching_rate

if __name__ == "__main__":
    if len(sys.argv) == 2:
        main(int(sys.argv[1]))
    else:
        main()

You can probably tell what this program does so I shall not elaborate. However, how can I edit the program so that it works for (for example) 4 goats and 1 car? Of course

DOORS = ['car', 'goat', 'goat']

needs to be changed but I'm not sure what else. Also, what does

return randrange(3)

do?

Thanks :)

[Gribouillis]

randrange(3) returns a random number in the set 0, 1, 2. You should replace that line with

return randrange(len(DOORS))

Other changes which seem obvious is to replace all the set([0,1,2]) by set(range(len(DOORS))) .

[pith]

Thanks for your help :)
I took your advice and tried the len(doors) but I get some indentation error. I have tried to modify the code for 5 doors (4 goats and 1 car) but it doesn't quite work:

#!/usr/bin/env python
"""
Monte Carlo simulation for the Monty Hall Problem:
http://en.wikipedia.org/wiki/Monty_Hall_problem.
"""
import sys
from random import randrange, shuffle, choice

DOORS = ['car', 'goat', 'goat', 'goat', 'goat']

def pick_door():
    """Return a number representing the player's first choice."""
    return randrange(5)

def reveal_door(pick):
    """Return the index of the door opened by the host.
    This cannot be a door hiding a car or the player's chosen door.
    """
    all_doors = set([0, 1, 2, 3, 4])
    unavailable_doors = set([DOORS.index('car'), pick])
    available_doors = list(all_doors - unavailable_doors)
    return choice(available_doors)

def staying_wins(pick):
    """Return True if the player won by staying
    with their first choice, False otherwise.
    """
    return won(pick)

def switching_wins(pick, open_door):
    """Return True if the player won by switching,
    False otherwise.
    """
    other_doors = set([pick, open_door])
    switched_pick = (set([0, 1, 2, 3, 4]) - other_doors).pop()
    return won(switched_pick)

def won(pick):
    """Return True if the player's final pick hides a car,
    False otherwise.
    """
    return (DOORS[pick] == 'car')

def main(iterations=10000):
    """Run the main simulation as many
    times as specified by the function argument.
    """
    shuffle(DOORS)

    switching = 0
    staying = 0

    for dummy in xrange(iterations):
        picked = pick_door()
        revealed = reveal_door(picked)
        if staying_wins(picked):
            staying += 1
        if switching_wins(picked, revealed):
            switching += 1

    staying_rate = (float(staying) / iterations) * 100
    switching_rate = (float(switching) / iterations) * 100

    print "Staying: %f%%" % staying_rate
    print "Switching: %f%%" % switching_rate

if __name__ == "__main__":
    if len(sys.argv) == 2:
        main(int(sys.argv[1]))
    else:
        main()

The strange thing is that I get different results each time I run the program. From 5 different runs I get:

>>> 
Staying: 19.310000%
Switching: 40.170000%
>>> 
Staying: 20.150000%
Switching: 79.850000%
>>> 
Staying: 19.800000%
Switching: 13.030000%
>>> 
Staying: 19.390000%
Switching: 13.720000%
>>> 
Staying: 19.690000%
Switching: 0.000000%
>>>

Perhaps it has something to do with the last part? I am not sure what

if __name__ == "__main__":
    if len(sys.argv) == 2:
        main(int(sys.argv[1]))
    else:
        main()

does.

Also I am not sure what this does:

for dummy in xrange(iterations):
        picked = pick_door()
        revealed = reveal_door(picked)
        if staying_wins(picked):
            staying += 1
        if switching_wins(picked, revealed):
            switching += 1

What does +=1 do?

Thanks in advance.