Instructions

In this homework, you are required to complete the problems described in section 3. The starter code for these problems is provided in hw06.py.

Submission: As instructed before, you need to submit your work with Ok by python3 ok --submit. You may submit more than once before the deadline, and your score of this assignment will be the highest one of all your submissions.

Readings: You might find the following references to the textbook useful:

Section 2.5

Required Problems

In this section, you are required to complete the problems below and submit your code to OJ website.

Remember, you can use ok to test your code:

$ python3 ok  # test all classes
$ python3 ok -q <class>  # test single class

Problem 1: Vending Machine (200pts)

Create a class called VendingMachine that represents a vending machine for some product. A VendingMachine object returns strings describing its interactions. Fill in the VendingMachine class, adding attributes and methods as appropriate, such that its behavior matches the following doctests:

class VendingMachine:
    """A vending machine that vends some product for some price.

    >>> v = VendingMachine('candy', 10)
    >>> v.vend()
    'Machine is out of stock.'
    >>> v.add_funds(15)
    'Machine is out of stock. Here is your $15.'
    >>> v.restock(2)
    'Current candy stock: 2'
    >>> v.vend()
    'You must add $10 more funds.'
    >>> v.add_funds(7)
    'Current balance: $7'
    >>> v.vend()
    'You must add $3 more funds.'
    >>> v.add_funds(5)
    'Current balance: $12'
    >>> v.vend()
    'Here is your candy and $2 change.'
    >>> v.add_funds(10)
    'Current balance: $10'
    >>> v.vend()
    'Here is your candy.'
    >>> v.add_funds(15) # Note: in such case, you should return all current funds
    'Machine is out of stock. Here is your $15.'

    >>> w = VendingMachine('soda', 2)
    >>> w.restock(3)
    'Current soda stock: 3'
    >>> w.restock(3)
    'Current soda stock: 6'
    >>> w.add_funds(2)
    'Current balance: $2'
    >>> w.vend()
    'Here is your soda.'
    """
    "*** YOUR CODE HERE ***"

You may find Python string formatting syntax or f-strings useful. A quick example:

>>> ten, twenty, thirty = 10, 'twenty', [30]
>>> '{0} plus {1} is {2}'.format(ten, twenty, thirty)
'10 plus twenty is [30]'

>>> feeling = 'love'
>>> course = 61
>>> f'I {feeling} {course}A!'
'I love 61A!'

Problem 2: Cat (100pts)

Below is a skeleton for the Cat class, which inherits from the Pet class. To complete the implementation, override the __init__ and talk methods and add a new lose_life method, such that its behavior matches the following doctests.

We may change the implementation of Pet while testing your code, so make sure you use inheritance correctly.

Hint: You can call the __init__ method of Pet to set a cat's name and owner.

class Pet:
    """A pet.

    >>> kyubey = Pet('Kyubey', 'Incubator')
    >>> kyubey.talk()
    Kyubey
    >>> kyubey.eat('Grief Seed')
    Kyubey ate a Grief Seed!
    """
    def __init__(self, name, owner):
        self.is_alive = True    # It's alive!!!
        self.name = name
        self.owner = owner
    
    def eat(self, thing):
        print(self.name + " ate a " + str(thing) + "!")
    
    def talk(self):
        print(self.name)


class Cat(Pet):
    """A cat.

    >>> vanilla = Cat('Vanilla', 'Minazuki Kashou')
    >>> isinstance(vanilla, Pet) # check if vanilla is an instance of Pet.
    True
    >>> vanilla.talk()
    Vanilla says meow!
    >>> vanilla.eat('fish')
    Vanilla ate a fish!
    >>> vanilla.lose_life()
    >>> vanilla.lives
    8
    >>> vanilla.is_alive
    True
    >>> for i in range(8):
    ...     vanilla.lose_life()
    >>> vanilla.lives
    0
    >>> vanilla.is_alive
    False
    >>> vanilla.lose_life()
    Vanilla has no more lives to lose.
    """
    def __init__(self, name, owner, lives=9):
        "*** YOUR CODE HERE ***"

    def talk(self):
        """ Print out a cat's greeting.
        """
        "*** YOUR CODE HERE ***"

    def lose_life(self):
        """Decrements a cat's life by 1. When lives reaches zero, 'is_alive'
        becomes False. If this is called after lives has reached zero, print out
        that the cat has no more lives to lose.
        """
        "*** YOUR CODE HERE ***"

Problem 3: Noisy Cat (100pts)

More cats! Fill in this implemention of a class called NoisyCat, which is just like a normal Cat. However, NoisyCat talks a lot -- twice as much as a regular Cat!

We may change the implementation of Pet and Cat while testing your code, so make sure you use inheritance correctly.

class NoisyCat: # Dose this line need to change?
    """A Cat that repeats things twice.

    >>> chocola = NoisyCat('Chocola', 'Minazuki Kashou')
    >>> isinstance(chocola, Cat) # check if chocola is an instance of Cat.
    True
    >>> chocola.talk()
    Chocola says meow!
    Chocola says meow!
    """
    def __init__(self, name, owner, lives=9):
        # Is this method necessary? If not, feel free to remove it.
        "*** YOUR CODE HERE ***"
    
    def talk(self):
        """Talks twice as much as a regular cat.
        """
        "*** YOUR CODE HERE ***"

Problem 4: Pretty Printer

Part 1

Your first task is to define pretty printer methods for Pet, Cat and NoisyCat.

We start with implementing functions named to_str for Pet, Cat, and NoisyCat classes.

For Pet, the output should be:

>>> kyubey = Pet('Kyubey', 'Incubator')
>>> kyubey.to_str()
'(Kyubey, Incubator)'

For Cat and NoisyCat, the output should be:

>>> vanilla = Cat('Vanilla', 'Minazuki Kashou')
>>> vanilla.to_str()
'(Vanilla, Minazuki Kashou, 9)'
>>> vanilla.lose_life()
>>> vanilla.to_str()
'(Vanilla, Minazuki Kashou, 8)'

Now, we could define a function pretty_print, which accepts an object and print it prettily (i.e. with color).

To colorfully print something in terminal, this simplest way is to use ANSI escape code.
class Colors:
    HEADER     = '\033[95m'
    OKBLUE     = '\033[34m'
    OKCYAN     = '\033[35m'
    OKGREEN    = '\033[96m'
    WARNING    = '\033[93m'
    FAIL       = '\033[91m'
    ENDC       = '\033[0m'
    BOLD       = '\033[1m'
    UNDERLINE  = '\033[4m'


>>> print(f"{Colors.OKBLUE}Hello, World{Colors.ENDC}")
Hello, World # this line should be blue
>>> print(f"{Colors.OKCYAN}Hello, World{Colors.ENDC}")
Hello, World # this line should be red
>>> print(f"{Colors.UNDERLINE}Hello, World{Colors.ENDC}")
Hello, World # this line should be underlined 
Windows Console may not be able to display that. Use vscode console or windows terminal instead.

For real world program, you should use a library to display colorful output. E.g. termcolor

pretty_print should print object with form type(to_str). The type is the class name of the input object, the to_str is the return value of object.to_str(). For example:

>>> kyubey = Pet('Kyubey', 'Incubator')
>>> pretty_print(kyubey)
Pet(Kyubey, Incubator)

example

We ignore the ascii escape code in examples, you can check the real output in doctest

Note:

type could be obtained by python builtin type(obj).__name__. E.g. type(kyubey).__name__ is Pet
The type part of the printed str should be displayed with color defined by Colors.OKBLUE. For most device/terminal, this color should be blue.
The to_str part of the printed str should be displayed with color defined by Colors.OKCYAN. For most device/terminal, this color should be like red.

Part 2

Your second task is to inject the defined pretty_print method to all Pet, Cat and NoisyCat classes. For example:

>>> kyubey = Pet('Kyubey', 'Incubator')
>>> kyubey.pp() # the same result as `pretty_print`
Pet(Kyubey, Incubator)

To support such method call,

define a class called PrintModule:

class PrintModule:
    def pp(self):
        pretty_print(self)

Editing the declaration of the Pet class.

Test your code with:

>>> kyubey = Pet('Kyubey', 'Incubator')
>>> kyubey.pp()
Pet(Kyubey, Incubator)
>>> vanilla = Cat('Vanilla', 'Minazuki Kashou')
>>> vanilla.pp()
Cat(Vanilla, Minazuki Kashou, 9)

This is an ugly implementation of mixin. You can check this page for ruby style mixin, which is clear and elegant.

Just for fun Problems

This section is out of scope for our course, so the problems below is optional. That is, the problems in this section don't count for your final score and don't have any deadline. Do it at any time if you want an extra challenge or some practice with higher order function and abstraction!

To check the correctness of your answer, you can submit your code to Contest 'Just for fun'.

Problem 4: Next Fibonacci Object (0pts)

Implement the next method of the Fib class. For this class, the value attribute is a Fibonacci number. The next method returns a Fib instance whose value is the next Fibonacci number. The next method should take only constant time.

You can assume we will neither create Fib instance with non-zero value directly nor edit the value of Fib instance outside the class.

Hint: Keep track of the previous number by setting a new instance attribute inside next. You can create new instance attributes for objects at any point, even outside the __init__ method.

class Fib:
    """A Fibonacci number.

    >>> start = Fib()
    >>> start.value
    0
    >>> start.next().value
    1
    >>> start.next().next().value
    1
    >>> start.next().next().next().value
    2
    >>> start.next().next().next().next().value
    3
    >>> start.next().next().next().next().next().value
    5
    >>> start.next().next().next().next().next().next().value
    8
    >>> start.value # Ensure start isn't changed
    0
    """
    def __init__(self, value=0):
        self.value = value

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

Homework 06: OOP and Inheritance