Simulates 5000 games of Craps and works out the probability of winning a game, and the average number of times the dice is rolled per game.

CrapsSimulation.py

from __future__ import division
import random

numRolls = 0 # Number of times the dice is rolled.

# generates a random number between 1 and 6, like rolling a 6 sided die.
def rollDice() :
    return random.randint(1, 6)

# Simulate this 5000 times, then to get the prob of winning, do (numb of times won/numb of times simumalted).
def sim() :
    global numRolls
    # Rolls two 6-sided die.
    dice1 = rollDice()
    dice2 = rollDice()
    numRolls += 1

    print( 'Dice1 = ' + str(dice1) )
    print( 'Dice2 = ' + str(dice2) )

    total = dice1 + dice2
    ref = 0

    # Immediate loss or immediate win.
    if total == 7 or total == 11 :
        return 'YOU WIN!'

    elif total == 2 or total == 3 or total == 12 :
        return 'YOU LOSE!'

    # Reference point
    elif total == 4 or total == 5 or total == 6 or total == 8 or total == 9 or total == 10 :
        ref = total
        print( 'ref point = ' + str( total ) )

        # Keep rolling two dice till you get same value as ref, then you win.
        # If you roll again and get 7, you lose.
        newRoll1 = rollDice()
        newRoll2 = rollDice()
        numRolls += 1

        newTotal = newRoll1 + newRoll2
        while newTotal != ref :
            newRoll1 = rollDice()
            newRoll2 = rollDice()
            numRolls += 1

            newTotal = newRoll1 + newRoll2
            print( 'newTotal = ' + str(newTotal) )
            if newTotal == 7 :
                return 'YOU LOSE!'
            if newTotal == ref :
                return 'YOU WIN!'
    else :
        return None

def main() :
    # Simulate 5000 times. Expect prob. of winning to be approx 0.49.
    numOfSims = 5000
    numOfWins = 0
    numOfLoss = 0

    for i in range(numOfSims) :
        game = sim()
        if game == 'YOU WIN!' :
            print('YOU WIN!')
            numOfWins = numOfWins + 1
        if game == 'YOU LOSE!' :
            print('YOU LOSE!')
            numOfLoss = numOfLoss + 1


    print('The number of wins = ' + str(numOfWins) )
    print('The number of losses = ' + str(numOfLoss))
    print('The number of sims = ' + str(numOfSims))
    prob = float(numOfWins / numOfSims)
    print('The probability of winning = ' + str(prob) )
    print('The dice was rolled ' + str(numRolls))
    print('On average, the dice is rolled ' + str(numRolls / numOfSims))

if __name__ == "__main__":
    main()