craps in python

I'm trying to simulate n games of craps. The code seems to make sense to me but I never get the right result. For example, if I put in n = 5 i.e. fives games the wins and losses 开发者_StackOverflow社区sum to something greater than 5.

Here's how it's supposed to work: if initial roll is 2, 3, or 12, the player loses. If the roll is 7 or 11, the player wins. Any other initial roll causes the player to roll again. He keeps rolling until either he rolls a 7 or the value of the initial roll. If he re-rolls the initial value before rolling a 7, it's a win. Rolling a 7 first is a loss.

from random import randrange

    def roll():
        dice = randrange(1,7) + randrange (1,7)
        return dice

    def sim_games(n):
        wins = losses = 0
        for i in range(n):
            if game():
                wins = wins + 1
            if not game():
                losses = losses + 1
        return wins, losses

    #simulate one game

    def game():

            dice = roll()
            if dice == 2 or dice == 3 or dice == 12:
                return False
            elif dice == 7 or dice == 11:
                return True
            else:
                dice1 = roll()
                while dice1 != 7 or dice1 != dice:
                    if dice1 == 7:
                        return False
                    elif dice1 == dice:
                        return True
                    else:
                        dice1 = roll()

    def main():

        n = eval(input("How many games of craps would you like to play? "))
        w, l = sim_games(n)

        print("wins:", w,"losses:", l)

---

The problem is with

        if game():
            wins = wins + 1
        if not game():
            losses = losses + 1

Instead, it should be

        if game():
            wins = wins + 1
        else:
            losses = losses + 1

In your code, you are simulating two games instead of one (by calling game() twice). This gives four possible outcomes instead of two (win/loss), giving inconsistent overall results.

---

In this code

for i in range(n):
    if game():
        wins = wins + 1
    if not game():
        losses = losses + 1

you call game() twice, so you play two games right there. What you want is a else block:

for i in range(n):
    if game():
        wins = wins + 1
    else:
        losses = losses + 1

Btw, you can simplify the logic with in:

def game():
    dice = roll()

    if dice in (2,3,12):
        return False

    if dice in (7,11):
        return True

    # keep rolling
    while True:
        new_roll = roll()

        # re-rolled the initial value => win
        if new_roll==dice:
            return True

        # rolled a 7 => loss
        if new_roll == 7:
            return False

        # neither won or lost, the while loop continues ..

The code is quite literally the description you gave.

---

Don't do this

    for i in range(n):
        if game():
            wins = wins + 1
        if not game():
            losses = losses + 1

It doesn't work out well at all.

---

There are numerous problems with this code. Most importantly, you're calling game() twice per loop. You need to call it once and store the result, and switch based on that.

---

An OO rewrite:

import random

try:
    rng = xrange   # Python 2.x
    inp = raw_input
except NameError:
    rng = range    # Python 3.x
    inp = input

def makeNSidedDie(n):
    _ri = random.randint
    return lambda: _ri(1,n)

class Craps(object):
    def __init__(self):
        super(Craps,self).__init__()
        self.die = makeNSidedDie(6)
        self.firstRes = (0, 0, self.lose, self.lose, 0, 0, 0, self.win, 0, 0, 0, self.win, self.lose)
        self.reset()

    def reset(self):
        self.wins   = 0
        self.losses = 0

    def win(self):
        self.wins += 1
        return True

    def lose(self):
        self.losses += 1
        return False

    def roll(self):
        return self.die() + self.die()

    def play(self):
        first = self.roll()
        res   = self.firstRes[first]
        if res:
            return res()
        else:
            while True:
                second = self.roll()
                if second==7:
                    return self.lose()
                elif second==first:
                    return self.win()

    def times(self, n):
        wins = sum(self.play() for i in rng(n))
        return wins, n-wins

def main():
    c = Craps()

    while True:
        n = int(inp("How many rounds of craps would you like to play? (0 to quit) "))
        if n:
            print("Won {0}, lost {1}".format(*(c.times(n))))
        else:
            break

    print("Total: {0} wins, {1} losses".format(c.wins, c.losses))

if __name__=="__main__":
    main()