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In Topic: Locating Bug in Craps Simulation

Posted 14 Mar 2012

Simown, on 14 March 2012 - 02:51 PM, said:

I think what Jack was getting at is that:

while diceValue != initValue or 7:

Is probably not equating to what you think. It is saying if diceValue is not equal to initValue or "if the number 7 is false". Given that an number that isn't 0 is true, it will equate to:

while diceValue != initValue or True:

Which I'm guessing is why they win every time.

That makes sense! I revised all of the control structures in the script and it runs smoothly now. I appreciate everybody's help. =)

Anyway, the updated source code is:

Spoiler

#!/usr/bin/env python
# craps-simulation.py - Craps Probability Simulation
#   Roll Values: 2 - 12
#   If initial roll is... 2, 3, 12 = LOSE or 7, 11 = WIN
#       Else, reroll until it hits... 7 = LOSE or Initial Value = WIN

import random

def main():
    printIntro()
    numOfGameSim = promptGameSim()
    # Simulate 'n' games and return numOfWins/probability
    numOfWins, winningPercentage = simulateGames(numOfGameSim)
    printStats(numOfGameSim, numOfWins, winningPercentage)
    
def printIntro():
    print "This script will simulate 'n' number of Craps games to calculate " \
    "\nan estimated winning probability."
    print
    
def promptGameSim():
    numOfGameSim = input("How many games would you like to simulate: ")
    return numOfGameSim

def simulateGames(numOfGameSim):
    numOfWins = 0 # Set Win Count to 0
    
    # Simulate 'n' games
    for i in range(numOfGameSim):
        diceValue = random.randrange(2, 13)
        initValue = diceValue
        
        if initValue == 7 or initValue == 11:
            numOfWins += 1
        elif initValue == 2 or initValue == 3 or initValue == 12:
            numOfWins += 0
        else:
            diceValue = 0 # Make diceValue != initValue to enter re-roll loop
            while diceValue != initValue and diceValue != 7:
                diceValue = random.randrange(2, 13)
            if diceValue == initValue:
                numOfWins += 1
            else:
                numOfWins += 0

    # return the win count and the winning probability    
    return numOfWins, (float(numOfWins) / float(numOfGameSim))

def printStats(numOfGameSim, numOfWins, winningPercentage):
    print "Out of %d games, there were %d wins. The probability of winning is %0.2f%%" % \
    (numOfGameSim, numOfWins, (winningPercentage * 100))
    print
    raw_input("Hit <Enter> to exit.")
    
if __name__ == '__main__':
    main()

The output also seems to agree with the craps winning probability (~49.3%):

Out of 1520 games, there were 745 wins. The probability of winning is 49.01%
Out of 1000 games, there were 468 wins. The probability of winning is 46.80%
Out of 500 games, there were 251 wins. The probability of winning is 50.20%

In Topic: Locating Bug in Craps Simulation

Posted 14 Mar 2012

JackOfAllTrades, on 14 March 2012 - 12:03 PM, said:

Try

while diceValue != initValue or diceValue == 7:

Wouldn't that just make the while loop keep looping until the diceValue == initValue? Correct me if I'm wrong, but that would yield the same results as while diceValue != initValue:.

If '7' is rolled, the while loop would just continue to re-roll for the initial value.

tlhIn`toq, on 14 March 2012 - 12:03 PM, said:

You need to throw the code into a debugger state so you can examine the value of the randomly generated number at this point.

I suspect that due to sheer speed of execution the new random is not actually a new number. Which would mean the second throw always matches the player's target point: Win!

Okay! I debugged my program with IDLE's debugger and some very bizarre things happened around here:

for i in range(numOfGameSim):
    diceValue = random.randrange(2, 13)
    initValue = diceValue
        
    if initValue == 7 or 11:
        numOfWins += 1

The program generated random numbers each run, but for some reason, executed these statements

if initValue == 7 or 11:
    numOfWins += 1

even if the condition was obviously false. After numOfWins += 1, the program went back to the top of the for loop and repeated the process for 'numOfGameSim' times adding 1 to numOfWins each time.

Spoiler

#!/usr/bin/env python
# craps-simulation.py - Craps Probability Simulation
#   Roll Values: 2 - 12
#   If initial roll is... 2, 3, 12 = LOSE or 7, 11 = WIN
#       Else, reroll until it hits... 7 = LOSE or Initial Value = WIN

import random

def main():
    printIntro()
    numOfGameSim = promptGameSim()
    # Simulate 'n' games and return numOfWins/probability
    numOfWins, winningPercentage = simulateGames(numOfGameSim)
    printStats(numOfGameSim, numOfWins, winningPercentage)
    
def printIntro():
    print "This script will simulate 'n' number of Craps games to calculate " \
    "\nan estimated winning probability."
    print
    
def promptGameSim():
    numOfGameSim = input("How many games would you like to simulate: ")
    return numOfGameSim

def simulateGames(numOfGameSim):
    numOfWins = 0 # Set Win Count to 0
    
    # Simulate 'n' games
    for i in range(numOfGameSim):
        diceValue = random.randrange(2, 13)
        initValue = diceValue
        
        if initValue == 7 or 11:
            numOfWins += 1
        elif initValue == 2 or 3 or 12:
            numOfWins += 0
        else:
            while diceValue != initValue or 7:
                diceValue = random.randrange(2, 13)
            if diceValue == initValue:
                numOfWins += 1
            else:
                numOfWins += 0

    # return the win count and the winning probability    
    return numOfWins, (float(numOfWins) / float(numOfGameSim))

def printStats(numOfGameSim, numOfWins, winningPercentage):
    print "Out of %d games, there were %d wins. The probability of winning is %d%%" % \
    (numOfGameSim, numOfWins, (winningPercentage * 100))
    print
    raw_input("Hit <Enter> to exit.")
    
if __name__ == '__main__':
    main()

^^^ Full Source Code ^^^

In Topic: Locating Bug in Craps Simulation

Posted 14 Mar 2012
tlhIn`toq, on 14 March 2012 - 09:24 AM, said:
Doesn't this mean the program will loop indefinatley until the player rolls a 7 or their point? Code won't continue to line 17 until the player wins.

Thanks for the reply! :)
```
while diceValue != initValue or 7:
    diceValue = random.randrange(2, 13)
```
Yes, this loop does continue to re-roll the die indefinitely until it hits the initial roll or a '7', but rolling a '7' would mean that the player loses the game. After re-rolling, the following if statements would determine which value the loop stopped at.
```
if diceValue == initValue:
   numOfWins += 1 # WIN
else:
   numOfWins += 0 # LOSE
```
If the while loop stopped when it rolled the initial value, a win would be recorded. Otherwise, the win would not be recorded because the while loop stopped on a '7'.

I don't see how the player could always win if rolling a '7' during the while loop does not count as a win.
In Topic: Comparing Python and C++: The "for loop"

Posted 11 Mar 2012

sepp2k, on 11 March 2012 - 09:40 AM, said:
What do you mean by "how is it possible"? Do you mean how would you implement it in C++?

Sorry, my question wasn't clear. I guess I was asking for a breakdown on how Python interprets the for loop, but the C++ equivalents that you both provided was adequate in helping me understand. =)

It also helped that you pointed out that "collection" in for var in collection: must be iterable. I was under the mindset that the conditions only worked with number variables. Thanks!
In Topic: Reading File... from Where?

Posted 10 Mar 2012
atraub, on 10 March 2012 - 08:57 PM, said:
It'll check the current working directory

Let me give you an example. let's say I don't have Python in my path (sue me, I don't) so I open up a prompt and I navigate to C:\Python27\ and typed in:

python C:\Users\Adam\Desktop\printfile.py

in this situation, Python would look for that file from C:\Python27\ because that is my current working directory.

On the other hand.

Let's say I navigate to C:\Users\Adam\Desktop\ and then ran this:

C:\Python31\python printfile.py

in this situation, it would look for the file in C:\Users\Adam\Desktop\ because that is my current directory.

EDIT:
Well wait a minute, let's say you have your pc set to run automatically when you double click it. Well, in that case it'll check your desktop. Here's a little script I wrote that you can use to confirm it. This script will print out the current working directory, which is where it'll look.
```
import os
input(os.getcwd())
```
I'm assuming you use Linux or Windows.
I tried testing out both scenarios, and I get it now. Thanks! Also, does it make a difference whether I execute the script in the command prompt or in IDLE?

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In Topic: Locating Bug in Craps Simulation

In Topic: Locating Bug in Craps Simulation

In Topic: Locating Bug in Craps Simulation

In Topic: Comparing Python and C++: The "for loop"

In Topic: Reading File... from Where?

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