"""
Represents one move, indicating a choice to cooperate or not
"""
class Move:

"""
constructor of a move: create/initialize the cooperate field.
"""
def __init__(self, cooperate=True):
   self.cooperate = cooperate

"""
return "." for a cooperating move, "x" for a non-cooperating move
"""
def __str__(self):
   if self.cooperate:
         return "."
   else:
         return "x"

"""
create/return a string as in this example: "Move(True)"
"""
def __repr__(self):
   return "Move(" + str(self.cooperate) + ")"

"""
return boolean: whether this move has same cooperate value as the other
"""
def __eq__(self, other):
   if isinstance(other, Move) and self.cooperate == other.cooperate:
         return True
   else:
         return False

"""
change the cooperation status of this move
"""
def change(self):
   self.cooperate = not self.cooperate

"""
create/return a new Move object that has the same cooperation status.
"""
def copy(self):
   return Move(self.cooperate)

"""
Represents any exceptional situation for players, with a message
stored inside of it.
"""
class PlayerException(Exception):

"""
create/initialize a msg field based on the parameter
"""
def __init__(self, msg):
   self.msg = msg

"""
Returns the error message
"""
def __str__(self):
   return self.msg

"""
return a string like this: "PlayerException('message contents')"
"""
def __repr__(self):
   return "PlayerException('" + self.msg + "')"

"""
Represents one player, whose style string will resolve their behavior.
A Player object keeps track of the needed internal state:
previous moves of the opponent, their style, and their points.
"""
class Player:

"""
create/initialize fields for each parameter.
If history is None, then re-assign an empty list to it.
"""
def __init__(self, style, points=0, history=None):
   self.style = style
   self.points = points
   if history is None:
         self.history = []
   else:
         self.history = history

   if style not in ["previous", "friend", "cheater", "grudger", "detective"]:
         raise PlayerException("no style '" + str(style) + "'.")

"""
create/return a string (utilizing Move's str) like: "friend(12)+.+.+..."
"""
def __str__(self):
   msg = self.style + "(" + str(self.points) + ")"
   for hist in self.history:
         msg += str(hist)
   return msg

"""
create/return a string like: "Player('grudge', 12, [Move(True), Move(False)])"
"""
def __repr__(self):
   msg = "Player('" + self.style + "', " + str(self.points)
   msg += ", ["
   idx = 0
   for hist in self.history:
         msg += repr(hist)
         if idx < len(self.history)-1:
            msg += ", "
         idx += 1
   msg += "])"
   return msg

"""
reset history to an empty list. Don't change points
"""
def reset_history(self):
   self.history = []

"""
reset history, and also reset points to zero
"""
def reset(self):
   self.reset_history()
   self.points = 0

"""
increase points by the parameter. Might go negative
"""
def update_points(self, amount):
   self.points += amount

"""
return whether an opponent ever cheated, based on the history
"""
def ever_betrayed(self):
   result = False
   for hist in self.history

Background: Classes allow us to define new types for Python. We ca...