Simulate several rounds of rock, paper and scissors

Question

I am trying to implement a function that takes an integer n and simulates n rounds of Rock, Paper, Scissors between players Player 1 and Player 2. The player who wins the most rounds wins the n-round game, with ties possible. The function should print the result of the game as shown.

    >>> simul(1)
    Player 1
    >>> simul(1)
    Tie
    >>>simul(100)
    Player 2

I think I need to approach this in a modular fashion. In other words, I need to combine at least 2 functions, my problem is that I can't seem to figure out how to do that. How can I activate the result from an embedded function when calling the simul() function?

So I have created a function that simulates the game Rock, Paper, Scissors by execution the function rps(p1, p2). The code is the following:

    def rps(p1,p2):
        #tie
        if (p1==p2):
            return 0
        # player 1 wins    
        elif p1+p2 in ['PR','RS','SP']:
            return -1
        else:
            return 1
        # player 2 wins

This is where I'm a bit stuck. I need to activate this function when executing the simul() function—how can I do that? What I have so far is the following:

    def rps(p1,p2):
    #tie
        if (p1==p2):
            return 0
    # player 1 wins    
        elif p1+p2 in ['PR','RS','SP']:
            return -1
        else:
            return 1
    # player 2 wins

    def choose_rps():
        import random
        random.choice('RPS')

    def simul(n):
        p1_wins, p2_wins = 0, 0
        for i in range(n):
            p1 = choose_rps()
            p2 = choose_rps()
            result = rps(p1, p2)
            if result == -1:
                p1_wins += 1
            elif result == 1:
                p2_wins += 1
            if p1_wins > p2_wins:
                return 'Player 1'
            elif p1_wins == p2_wins:
                return 'Tie'
            else:
                return 'Player 2'

Answer 1

Here is an equivalent function without the RPS narrative:

import random

def simul(n):
    score = sum([random.choice([-1, 0, 1]) for i in xrange(n)])
    winner_idx = 0 if score > 0 \
            else 1 if score < 0 \
            else 2
    print ['Player 1', 'Player 2', 'Tie'][winner_idx]

Here is one that follows the story and is expanded to Rock, Paper, Scissors, Lizard, Spock:

import random

def rand_RPSLK():
    while True:
        yield random.choice('PSKLR')

def simul(n):
    p1 = rand_RPSLK()
    p2 = rand_RPSLK()
    choice = lambda px: 'PSKLR'.index(next(px))
    score = sum([[0,1,-1,1,-1][choice(p1)-choice(p2)] for i in xrange(n)])
    winner_idx = 0 if score > 0 \
            else 1 if score < 0 \
            else 2
    print ['Player 1', 'Player 2', 'Tie'][winner_idx]

Answer 2

To "activate" a function, you just call it. For example:

def simul(n):
    score = 0
    for i in range(n):
        p1 = choose_rps()
        p2 = choose_rps()
        result = rps(p1, p2)
        score += result
    if score < 0:
        print('Player 1')
    elif score == 0:
        print('Tie')
    else:
        print('Player 2')

Of course you need to write the choose_rps function (which randomly chooses and returns one of R, P, or S)—but, as you can see, you just call it the same way as the rps function.

---

To put it all together into a script:

def rps(p1, p2):
    # ... your code here

def choose_rps():
    # implement this here

def simul(n):
    # code from above

And then you'll probably want something to drive it, such as this:

if __name__ == '__main__':
    import sys
    n = int(sys.argv[1]) if len(sys.argv) > 1 else 5
    simul(n)

… or…

while True:
    n = int(input('How many trials?')) # raw_input for Python 2.x
    simul(n)

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If you want, you can simplify this further. For example, you can turn the whole loop into a sum call with a generator expression:

def simul(n):
    score = sum(rps(choose_rps(), choose_rps()) for _ in range(n))