Due by 11/9/2018


Download hw10.zip. Inside the archive, you will find starter files for the questions in this homework, along with a copy of the OK autograder.

Submission: When you are done, submit the homework by uploading the hw10.py file to okpy.org. You may submit more than once before the deadline; only the final submission will be scored.

Readings: This homework relies on following references:

Question 1: Person

Modify the following Person class to add a repeat method, which repeats the last thing said. If nothing has been said yet, you can have repeat return a string of your choosing. See the doctests for an example of its use.

Hint: you will have to modify other methods as well, not just the repeat method.

class Person(object):
    """Person class.

    >>> steven = Person("Steven")
    >>> steven.say("Hello")
    >>> steven.repeat()
    >>> steven.greet()
    'Hello, my name is Steven'
    >>> steven.repeat()
    'Hello, my name is Steven'
    >>> steven.ask("preserve abstraction barriers")
    'Would you please preserve abstraction barriers'
    >>> steven.repeat()
    'Would you please preserve abstraction barriers'
    def __init__(self, name):
        self.name = name
        "*** YOUR CODE HERE ***"

    def say(self, stuff):
        "*** YOUR CODE HERE ***"
        return stuff

    def ask(self, stuff):
        return self.say("Would you please " + stuff)

    def greet(self):
        return self.say("Hello, my name is " + self.name)

    def repeat(self):
        "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q Person --local

Question 2: Mint

Complete the Mint and Coin classes so that the coins created by a mint have the correct year and worth.

  • Each Mint instance has a year stamp. The update method sets the year stamp to the current_year class attribute of the Mint class.
  • The create method takes a subclass of Coin and returns an instance of that class stamped with the mint's year (which may be different from Mint.current_year if it has not been updated.)
  • A Coin's worth method returns the cents value of the coin plus one extra cent for each year of age beyond 50. A coin's age can be determined by subtracting the coin's year from the current_year class attribute of the Mint class.

Use OK to test your code:

python3 ok -q Mint --local
class Mint:
    """A mint creates coins by stamping on years.

    The update method sets the mint's stamp to Mint.current_year.

    >>> mint = Mint()
    >>> mint.year
    >>> dime = mint.create(Dime)
    >>> dime.year
    >>> Mint.current_year = 2100  # Time passes
    >>> nickel = mint.create(Nickel)
    >>> nickel.year     # The mint has not updated its stamp yet
    >>> nickel.worth()  # 5 cents + (85 - 50 years)
    >>> mint.update()   # The mint's year is updated to 2100
    >>> Mint.current_year = 2175     # More time passes
    >>> mint.create(Dime).worth()    # 10 cents + (75 - 50 years)
    >>> Mint().create(Dime).worth()  # A new mint has the current year
    >>> dime.worth()     # 10 cents + (160 - 50 years)
    >>> Dime.cents = 20  # Upgrade all dimes!
    >>> dime.worth()     # 20 cents + (160 - 50 years)

    current_year = 2015

    def __init__(self):

    def create(self, kind):
        "*** YOUR CODE HERE ***"

    def update(self):
        "*** YOUR CODE HERE ***"

class Coin:
    def __init__(self, year):
        self.year = year

    def worth(self):
        "The worth is a coin's face value + 1 cent for each year over age 50."
        "*** YOUR CODE HERE ***"

class Nickel(Coin):
    cents = 5

class Dime(Coin):
    cents = 10