Homework 3
Due at 11:59:59 pm on Sunday, 9/25/2020.

hw03.zip

Instructions

Download hw03.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:

Questions

Question 1: Nonzero

Write a function that takes in a list and returns the first nonzero entry.

def nonzero(lst):
    """ Returns the first nonzero element of a list

    >>> nonzero([1, 2, 3])
    1
    >>> nonzero([0, 1, 2])
    1
    >>> nonzero([0, 0, 0, 0, 0, 0, 5, 0, 6])
    5
    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q nonzero

Question 2: Contains N

Write a function that takes in a list and a number, and returns whether or not the list contains the value n. 

def has_n(lst, n):
    """ Returns whether or not a list contains the value n.

    >>> has_n([1, 2, 2], 2)
    True
    >>> has_n([0, 1, 2], 3)
    False
    >>> has_n([], 5)
    False
    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q has_n

Question 3: Deep List

Implement the function deep_list, which takes in a list, and returns a new list which contains only elements of the original list that are also lists. Use a list comprehension.

def deep_list(seq):
    """Returns a new list containing elements of the original list that are lists.

    >>> seq = [49, 8, 2, 1, 102]
    >>> deep_list(seq)
    []
    >>> seq = [[500], [30, 25, 24], 8, [0]]
    >>> deep_list(seq)
    [[500], [30, 25, 24], [0]]
    >>> seq = ["hello", [12, [25], 24], 8, [0]]
    >>> deep_list(seq)
    [[12, [25], 24], [0]]
    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q deep_list

Question 4: Total Price

Implement the function total_price, which takes in a list of prices of individual products and needs to find the total price. Unfortunately, any product that is priced greater than or equal to $20 has a 50 percent tax, so include that in the final price.

Try to do this in one line!

Cast your final answer to an integer to avoid floating point precision errors. For example, if x contains your final answer, return int(x)!

def total_price(prices):
    """
    Finds the total price of all products in prices including a
    50% tax on products with a price greater than or equal to 20.
    >>> total_price([5, 20, 30, 7])
    87
    >>> total_price([8, 4, 3])
    15
    >>> total_price([10, 100, 4])
    164
    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q total_price

Question 5: arange

Implement the function arange, which behaves just like np.arange(start, end, step) from Data 8. You only need to support positive values for step.

def arange(start, end, step=1):
    """
    arange behaves just like np.arange(start, end, step).
    You only need to support positive values for step.

    >>> arange(1, 3)
    [1, 2]
    >>> arange(0, 25, 2)
    [0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24]
    >>> arange(999, 1231, 34)
    [999, 1033, 1067, 1101, 1135, 1169, 1203]

    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q arange

Question 6: Coordinates

Implement a function coords, which takes a function, a sequence, and an upper and lower bound on output of the function. coords then returns a list of x, y coordinate pairs (lists) such that:

  • Each pair contains [x, fn(x)]
  • The x coordinates are the elements in the sequence
  • Only pairs whose y coordinate is within the upper and lower bounds (inclusive)

See the doctests for examples.

One other thing: your answer can only be one line long. You should make use of list comprehensions!

def coords(fn, seq, lower, upper):
    """
    >>> seq = [-4, -2, 0, 1, 3]
    >>> def fn(x):
    ...     return x**2
    >>> coords(fn, seq, 1, 9)
    [[-2, 4], [1, 1], [3, 9]]
    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q coords

Optional Practice Question

Question 7: Adding matrices

To practice, write a function that adds two matrices together using list comprehensions. The function should take in two 2D lists of the same dimensions. Try to implement this in one line!

def add_matrices(x, y):
    """
    >>> matrix1 = [[1, 3],
    ...            [2, 0]]
    >>> matrix2 = [[-3, 0],
    ...            [1, 2]]
    >>> add_matrices(matrix1, matrix2)
    [[-2, 3], [3, 2]]
    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q add_matrices