Homework 11
Due at 11:59:59 pm on Friday, 11/29/2021.

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

Iterator/Generator Questions

Question 1: Restart

Implement an iterator class called IteratorRestart that will reset to the beginning when __iter__ is called again.

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 2: Hailstone

Write a generator that outputs the hailstone sequence from Lab 01.

Here's a quick remainder of how the hailstone sequence is defined:

1. Pick a positive integer n as the start.
2. If n is even, divide it by 2.
3. If n is odd, multiply it by 3 and add 1.
4. Continue this process until n is 1.

def hailstone(n):
    """
    >>> for num in hailstone(10):
    ...     print(num)
    ...
    10
    5
    16
    8
    4
    2
    1
    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q hailstone

Question 3: Generate permutations

Given a list of unique elements, a permutation of the list is a reordering of the elements. For example, [2, 1, 3], [1, 3, 2], and [3, 2, 1] are all permutations of the list [1, 2, 3].

Implement generate_perms, a generator function which takes in a lst and yields all the unique permutations of lst one at a time (see doctest for examples).

def generate_perms(lst):
    """
    Generates the permutations of lst one by one.
    >>> perms = generate_perms([1, 2, 3])
    >>> hasattr(perms, '__next__')
    True
    >>> p = list(perms)
    >>> p.sort()
    >>> p
    [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]
    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q generate_perms

Submit

Make sure to submit this assignment by running:

python3 ok --submit