Homework 11

Due at 11:59:59 pm on Saturday, 04/26/2020.

Instructions

Download hw11.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 with python3 ok --submit. You may submit more than once before the deadline; only the final submission will be scored. Check that you have successfully submitted your code on okpy.org. See this article for more instructions on okpy and submitting assignments.

Readings: This homework relies on following references:

• Section 4.2

Question 1: Scale

Implement an iterator class called ScaleIterator that scales elements in an iterable s by a number k.

class ScaleIterator:
    """An iterator the scales elements of the iterable s by a number k.

    >>> s = ScaleIterator([1, 5, 2], 5)
    >>> list(s)
    [5, 25, 10]

    >>> m = ScaleIterator(naturals(), 2)
    >>> [next(m) for _ in range(5)]
    [2, 4, 6, 8, 10]
    """
    def __init__(self, s, k):
        "*** YOUR CODE HERE ***"

    def __iter__(self):
        return self

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

Use OK to test your code:

python3 ok -q ScaleIterator

Question 2: Restart

Implement an iterator class called IteratorRestart that will reset to the beginning, unlike a normal Iterator that would throw a StopIteration Exception at the end.

class IteratorRestart:
    """
    >>> iterator = IteratorRestart(2, 7)
    >>> for num in iterator:
    ...     print(num)
    2
    3
    4
    5
    6
    7
    >>> for num in iterator:
    ...     print(num)
    2
    3
    4
    5
    6
    7
    """
    def __init__(self, start, end):
        "*** YOUR CODE HERE ***"

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

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

Use OK to test your code:

python3 ok -q IteratorRestart

Question 3: Scale

Implement the generator function scale(s, k), which yields elements of the given iterable s, scaled by k.

def scale(s, k):
    """Yield elements of the iterable s scaled by a number k.

    >>> s = scale([1, 5, 2], 5)
    >>> type(s)
    <class 'generator'>
    >>> list(s)
    [5, 25, 10]

    >>> m = scale(naturals(), 2)
    >>> [next(m) for _ in range(5)]
    [2, 4, 6, 8, 10]
    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q scale

Question 4: Remainder generator

Like functions, generators can also be higher-order. For this problem, we will be writing remainders_generator, which yields a series of generator objects.

remainders_generator takes in an integer m, and yields m different generators. The first generator is a generator of multiples of m, i.e. numbers where the remainder is 0. The second, a generator of natural numbers with remainder 1 when divided by m. The last generator yield natural numbers with remainder m - 1 when divided by m.

def remainders_generator(m):
    """
    Takes in an integer m, and yields m different remainder groups
    of m.

    >>> remainders_mod_four = remainders_generator(4)
    >>> for rem_group in remainders_mod_four:
    ...     for _ in range(3):
    ...         print(next(rem_group))
    0
    4
    8
    1
    5
    9
    2
    6
    10
    3
    7
    11
    """
    "*** YOUR CODE HERE ***"

Note that if you have implemented this correctly, each of the generators yielded by remainder_generator will be infinite - you can keep calling next on them forever without running into a StopIteration exception.

Hint: Consider defining an inner generator function. What arguments should it take in? Where should you call it?

Use OK to test your code:

python3 ok -q remainders_generator

Question 5: Project

Nothing to submit for this question, just a reminder to work on your project! The checkpoint is due April 22nd! Good luck!