Homework 8 Solutions

hw08.zip

Solution Files

You can find the solutions in hw08.py.

Required Questions

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Inheritance

Election

Let's implement a game called Election. In this game, two players compete to try and earn the most votes. Both players start with 0 votes and 100 popularity.

The two players alternate turns, and the first player starts. Each turn, the current player chooses an action. There are two types of actions:

The player can debate, and either gain or lose 50 popularity. If the player has popularity p1 and the other player has popularity p2, then the probability that the player gains 50 popularity is max(0.1, p1 / (p1 + p2)). Note that the max here ensures that the probability is never lower than 0.1.
The player can give a speech. If the player has popularity p1 and the other player has popularity p2, then the player gains p1 // 10 votes and popularity and the other player loses p2 // 10 popularity.

The game ends when a player reaches 50 votes, or after a total of 10 turns have been played (each player has taken 5 turns). Whoever has more votes at the end of the game is the winner!

Q1: Player

First, let's implement the Player class. Fill in the debate and speech methods, that take in another Player other, and implement the correct behavior as detailed above. Here are a few additional things to keep in mind:

Each player carries a random number generator (the random_func instance attribute), which is a function that returns a random float between 0 and 1 when called.
In the debate method, you should call the random_func function to get a random number. The player should gain 50 popularity if the random number is smaller than the probability described above, or lose 50 popularity otherwise.
Neither players' popularity should ever become negative. If this happens, set it equal to 0 instead.

### Phase 1: The Player Class
class Player:
    """
    >>> random = make_test_random()
    >>> p1 = Player('Hill', random)
    >>> p2 = Player('Don', random)
    >>> p1.popularity
    100
    >>> p1.debate(p2)  # random() should return 0.0
    >>> p1.popularity
    150
    >>> p2.popularity
    100
    >>> p2.votes
    0
    >>> p2.speech(p1)
    >>> p2.votes
    10
    >>> p2.popularity
    110
    >>> p1.popularity
    135
    >>> p1.speech(p2)
    >>> p1.votes
    13
    >>> p1.popularity
    148
    >>> p2.votes
    10
    >>> p2.popularity
    99
    >>> for _ in range(4):  # 0.1, 0.2, 0.3, 0.4
    ...     p1.debate(p2)
    >>> p2.debate(p1)
    >>> p2.popularity
    49
    >>> p2.debate(p1)
    >>> p2.popularity
    0
    """
    def __init__(self, name, random_func):
        self.name = name
        self.votes = 0
        self.popularity = 100
        self.random_func = random_func

    def debate(self, other):
        prob = max(0.1, self.popularity / (self.popularity + other.popularity))
        if self.random_func() < prob:
            self.popularity += 50
        else:
            self.popularity = max(0, self.popularity - 50)
    def speech(self, other):
        self.votes += self.popularity // 10
        self.popularity += self.popularity // 10
        other.popularity = max(0, other.popularity - (other.popularity // 10))
    def choose(self, other):
        return self.speech

Use Ok to test your code:

python3 ok -q Player

Q2: Game

Now, implement the Game class. Fill in the play method, which should alternate between the two players, starting with p1, and have each player take one turn at a time. The choose method in the Player class returns the method, either debate or speech, that should be called to perform the action.

In addition, fill in the winner method, which should return the player with more votes, or None if the players are tied.

### Phase 2: The Game Class
class Game:
    """
    >>> random = make_test_random()
    >>> p1, p2 = Player('Hill',random), Player('Don', random)
    >>> g = Game(p1, p2)
    >>> winner = g.play()
    >>> p1 is winner
    True
    >>> # Additional correctness tests
    >>> winner is g.winner()
    True
    >>> g.turn
    10
    >>> p1.votes = p2.votes
    >>> print(g.winner())
    None
    """
    def __init__(self, player1, player2):
        self.p1 = player1
        self.p2 = player2
        self.turn = 0

    def play(self):
        while not self.game_over():
            if self.turn % 2 == 0:
                curr, other = self.p1, self.p2
            else:
                curr, other = self.p2, self.p1
            curr.choose(other)(other)
            self.turn += 1        return self.winner()

    def game_over(self):
        return max(self.p1.votes, self.p2.votes) >= 50 or self.turn >= 10

    def winner(self):
        if self.p1.votes > self.p2.votes:
            return self.p1
        elif self.p2.votes > self.p1.votes:
            return self.p2
        else:
            return None

Use Ok to test your code:

python3 ok -q Game

Q3: New Players

The choose method in the Player class is boring because it always returns the speech method. Let's implement two new classes that inherit from Player, but have more interesting choose methods.

Implement the choose method in the AggressivePlayer class, which returns the debate method if the player's popularity is less than or equal to other's popularity, and speech otherwise. Also implement the choose method in the CautiousPlayer class, which returns the debate method if the player's popularity is 0, and speech otherwise.

### Phase 3: New Players
class AggressivePlayer(Player):
    """
    >>> random = make_test_random()
    >>> p1, p2 = AggressivePlayer('Don', random), Player('Hill', random)
    >>> g = Game(p1, p2)
    >>> winner = g.play()
    >>> p1 is winner
    True
    >>> # Additional correctness tests
    >>> p1.popularity = p2.popularity
    >>> p1.choose(p2) == p1.debate
    True
    >>> p1.popularity += 1
    >>> p1.choose(p2) == p1.debate
    False
    >>> p2.choose(p1) == p2.speech
    True
    """
    def choose(self, other):
        if self.popularity <= other.popularity:
            return self.debate
        else:
            return self.speech

Use Ok to test your code:

python3 ok -q AggressivePlayer

class CautiousPlayer(Player):
    """
    >>> random = make_test_random()
    >>> p1, p2 = CautiousPlayer('Hill', random), AggressivePlayer('Don', random)
    >>> p1.popularity = 0
    >>> p1.choose(p2) == p1.debate
    True
    >>> p1.popularity = 1
    >>> p1.choose(p2) == p1.debate
    False
    >>> # Additional correctness tests
    >>> p2.choose(p1) == p2.speech
    True
    """
    def choose(self, other):
        if self.popularity == 0:
            return self.debate
        else:
            return self.speech

Use Ok to test your code:

python3 ok -q CautiousPlayer

Linked Lists

Q4: Store Digits

Write a function store_digits that takes in an integer n and returns a linked list containing the digits of n in the same order (from left to right).

Important: Do not use any string manipulation functions, such as str or reversed.

def store_digits(n):
    """Stores the digits of a positive number n in a linked list.

    >>> s = store_digits(1)
    >>> s
    Link(1)
    >>> store_digits(2345)
    Link(2, Link(3, Link(4, Link(5))))
    >>> store_digits(876)
    Link(8, Link(7, Link(6)))
    >>> store_digits(2450)
    Link(2, Link(4, Link(5, Link(0))))
    >>> store_digits(20105)
    Link(2, Link(0, Link(1, Link(0, Link(5)))))
    >>> # a check for restricted functions
    >>> import inspect, re
    >>> cleaned = re.sub(r"#.*\\n", '', re.sub(r'"{3}[\s\S]*?"{3}', '', inspect.getsource(store_digits)))
    >>> print("Do not use str or reversed!") if any([r in cleaned for r in ["str", "reversed"]]) else None
    """
    result = Link.empty
    while n > 0:
        result = Link(n % 10, result)
        n //= 10
    return result

Use Ok to test your code:

python3 ok -q store_digits

Q5: Mutable Mapping

Implement deep_map_mut(func, s), which applies the function func to each element in the linked list s. If an element is itself a linked list, recursively apply func to its elements as well.

Your implementation should mutate the original linked list. Do not create any new linked lists. The function returns None.

Hint: You can use the built-in isinstance function to determine if an element is a linked list.
>>> s = Link(1, Link(2, Link(3, Link(4))))
>>> isinstance(s, Link)
True
>>> isinstance(s, int)
False

Construct Check: The final test case for this problem checks that your function does not create any new linked lists. If you are failing this doctest, make sure that you are not creating link lists by calling the constructor, i.e.
s = Link(1)

def deep_map_mut(func, s):
    """Mutates a deep link s by replacing each item found with the
    result of calling func on the item. Does NOT create new Links (so
    no use of Link's constructor).

    Does not return the modified Link object.

    >>> link1 = Link(3, Link(Link(4), Link(5, Link(6))))
    >>> print(link1)
    <3 <4> 5 6>
    >>> # Disallow the use of making new Links before calling deep_map_mut
    >>> Link.__init__, hold = lambda *args: print("Do not create any new Links."), Link.__init__
    >>> try:
    ...     deep_map_mut(lambda x: x * x, link1)
    ... finally:
    ...     Link.__init__ = hold
    >>> print(link1)
    <9 <16> 25 36>
    """
    if s is Link.empty:
        return None
    elif isinstance(s.first, Link):
        deep_map_mut(func, s.first)
    else:
        s.first = func(s.first)
    deep_map_mut(func, s.rest)

Use Ok to test your code:

python3 ok -q deep_map_mut

Check Your Score Locally

You can locally check your score on each question of this assignment by running

python3 ok --score

This does NOT submit the assignment! When you are satisfied with your score, submit the assignment to Gradescope to receive credit for it.

Submit Assignment

Submit this assignment by uploading any files you've edited to the appropriate Gradescope assignment. Lab 00 has detailed instructions.