Homework 4
Due at 11:59:59 pm on Thursday, September 29.

Instructions

Download hw04.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.

Readings: This homework relies on following references:

• Section 1.6

Lambdas

Question 1: Make your own lambdas

For each of the following expressions, write functions f1, f2, f3, and f4 such that the evaluation of each expression succeeds, without causing an error. Be sure to use lambdas in your function definition instead of nested def statements. Each function should have a one line solution.

f1 takes in nothing and returns 3. f2 takes in nothing and returns a function that takes in nothing and returns 3. f3 takes in nothing and returns a function that takes in 1 value and returns that same value.

f4 takes in nothing and returns a function. This function takes in nothing and returns another function. This next function takes in a value and returns yet another function. This final function takes in nothing and returns the value passed into the previous function (if this explanation is confusing, have a look at the doctest, and it might be more clear).

def f1():
    """
    >>> f1()
    3
    """
    "*** YOUR CODE HERE ***"

def f2():
    """
    >>> f2()()
    3
    """
    "*** YOUR CODE HERE ***"

def f3():
    """
    >>> f3()(3)
    3
    """
    "*** YOUR CODE HERE ***"

def f4():
    """
    >>> f4()()(3)()
    3
    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q f1
python3 ok -q f2
python3 ok -q f3
python3 ok -q f4

Question 2: Higher Order Lambdas

Return a lambda function that takes in a multiplier (the multiplier is a number) and returns a lambda function that will take in another number and will return the new input multiplied by the multiplier.

def higher_order_lambdas():
    """
    Return a lambda function that takes in a multiplier and returns a lambda function that given an input will 
    return the input multiplied by the multiplier
    >>> hol = higher_order_lambdas()
    >>> doubles = hol(2)
    >>> doubles(3)
    6
    >>> hol = higher_order_lambdas()
    >>> triples = hol(3)
    >>> triples(4)
    12
    """
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q higher_order_lambdas

Question 3: Lambdas and Currying

We can transform multiple-argument functions into a chain of single-argument, higher order functions by taking advantage of lambda expressions. This is useful when dealing with functions that take only single-argument functions. We will see some examples of these later on.

Write a function lambda_curry2 that will curry any two argument function fn using lambdas. See the doctest if you're not sure what this means.

def lambda_curry2(fn):
    """
    Returns a Curried version of a two argument function func.
    >>> from operator import add
    >>> x = lambda_curry2(add)
    >>> y = x(3)
    >>> y(5)
    8
    """
    "*** YOUR CODE HERE ***"
    

Use OK to test your code:

python3 ok -q lambda_curry2

Dictionaries

Question 4: Replace All

Given a dictionary d, return a new dictionary where all occurences of x as a value (not a key) is replaced with y.

def replace_all(d, x, y):
    """
    >>> d = {'foo': 2, 'bar': 3, 'garply': 3, 'xyzzy': 99}
    >>> e = replace_all(d, 3, 'poof')
    >>> e == {'foo': 2, 'bar': 'poof', 'garply': 'poof', 'xyzzy': 99}
    True
    """
    "*** YOUR CODE HERE ***"
    

Use OK to test your code:

python3 ok -q replace_all

Question 5: Merge Dictionaries

Implement the function merge_dict. The merge_dict function merges two dictionaries with the same keys together by adding up their values for the corresponding keys and returning the resulting dictionary.

def merge_dict(d1, d2):
    """Returns a dictionary that is the result of two dictionaries being merged together. 
    Dictionaries are merged by adding up their values. You can assume that the same keys 
    appear in both dictionaries.
    >>> data8 = {"midterms":1, "projects":3}
    >>> data100 = {"midterms":2, "projects":3}
    >>> combined_exams = merge_dict(data8, data100)
    >>> combined_exams
    {'midterms': 3, 'projects': 6}
    >>> sunday_orders = {"pizza": 3, "hot dogs": 2, "fries": 5}
    >>> monday_orders = {"pizza": 1, "hot dogs": 1, "fries": 8}
    >>> combined_orders = merge_dict(sunday_orders, monday_orders)
    >>> combined_orders
    {'pizza': 4, 'hot dogs': 3, 'fries': 13}
    """
    "*** YOUR CODE HERE ***"
    

Use OK to test your code:

python3 ok -q merge_dict

Submit

Make sure to submit this assignment by running:

python3 ok --submit