In [107]:

    

%matplotlib inline

import numpy.random
import matplotlib.pyplot as plt


    

In [108]:

    

# Setup payoffs
payoff_map = {("NC", "NC"): (-1, -1),
             ("NC", "C"): (-10, 0),
             ("C", "NC"): (0, -10),
             ("C", "C"): (-4, -4)}


    

In [109]:

    

my_payoff, your_payoff = payoff_map[("NC", "C")]
print("I got {0}".format(my_payoff))
print("You got {0}".format(your_payoff))


    

    




I got -10
You got 0

In [282]:

    

prob_confess = 0.5

class Player(object):
    """
    Player object.
    """
    
    def __init__(self, payoff_map, prob_confess):
        """
        Constructor
        """
        self.payoff_map = payoff_map
        self.prob_confess = prob_confess
        self.previous_game_payoffs = []
        self.other_player_action = []
        
    def get_action(self):
        """
        Randomly draw action given prob_confess.
        """
        if numpy.random.random() <= prob_confess:
            return "C"
        else:
            return "NC"
        

class AlwaysCUntilDPlayer(object):
    """
    Always cooperates until the other defects.
    
    N.B.: We'll learn about inheritance later.
    """
    def __init__(self, payoff_map, memory=None):
        """
        Constructor
        """
        self.payoff_map = payoff_map
        self.memory = memory
        self.previous_game_payoffs = []
        self.other_player_action = []
        
    def get_action(self):
        """
        Randomly draw action given prob_confess.
        """
        if self.memory: 
            if self.other_player_action[(-self.memory):].count("C") > 0:
                return "C"
            else:
                return "NC"
        else:
            if self.other_player_action.count("C") > 0:
                return "C"
            else:
                return "NC"


    

In [140]:

    

player_a = Player(payoff_map, prob_confess)
player_b = Player(payoff_map, prob_confess)


    

In [128]:

    

player_a.get_action()


    

    
Out[128]:





'C'

In [141]:

    

class Game(object):
    """
    Game class which stores the two players, their actions, and outcome.
    """
    
    def __init__(self, player_a, player_b):
        """
        Constructor
        """
        self.player_a = player_a
        self.player_b = player_b
        
    def run(self):
        """
        Run the game.
        """
        # Draw the actions/strategies of the players
        self.strategy_a = self.player_a.get_action()
        self.strategy_b = self.player_b.get_action()
        
        # Calculate the outcomes
        self.payoff_a, self.payoff_b = payoff_map[(self.strategy_a, self.strategy_b)]
        self.total_payoff = self.payoff_a + self.payoff_b
        self.average_payoff = (self.payoff_a + self.payoff_b) / 2.0
        
        # Update player memories
        self.player_a.previous_game_payoffs.append(self.payoff_a)
        self.player_b.previous_game_payoffs.append(self.payoff_b)
        self.player_a.other_player_action.append(self.strategy_b)
        self.player_b.other_player_action.append(self.strategy_a)


    

In [289]:

    

# Create players
player_a = Player(payoff_map, prob_confess)
player_b = AlwaysCUntilDPlayer(payoff_map, memory=50)


    

In [290]:

    

# Create the game
g = Game(player_a, player_b)

# Run the game
g.run()

print("The strategies were {0}, {1}".format(g.strategy_a, g.strategy_b))
print("The total payoff was {0} and the average payoff was {1}"\
        .format(g.total_payoff, g.average_payoff))
print(player_a.other_player_action)


    

    




The strategies were NC, NC
The total payoff was -2 and the average payoff was -1.0
['NC']

In [291]:

    

# Set number of games to run
num_games = 100
game_history = []
total_payoff_history = []

# Create players
player_a = Player(payoff_map, prob_confess)
player_b = Player(payoff_map, prob_confess)

for i in range(num_games):
    # Create and run the game
    g = Game(player_a, player_b)
    g.run()
    
    # Append to the history
    total_payoff_history.append(g.total_payoff)
    game_history.append(g)


    

In [ ]:

    




    

In [292]:

    

__ = plt.hist(total_payoff_history)


    

In [293]:

    

plt.plot(total_payoff_history)


    

    
Out[293]:





[<matplotlib.lines.Line2D at 0x7fe10f2e31d0>]






    

In [ ]: