Solutions: You can find the file with solutions for all questions here.

Required questions

Question 1: 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]

    """
    return [n for n in range(start, end, step)]

Use OK to test your code:

python3 ok -q arange

Question 2: Flight of the Bumblebee

Write a function that takes in a number n and returns a function that takes in a number m which will print all numbers from 0 to m - 1 (including 0 but excluding m) but print Buzz! instead for all the numbers that are divisible by n.

def make_buzzer(n):
    """ Returns a function that prints numbers in a specified
    range except those divisible by n.

    >>> i_hate_fives = make_buzzer(5)
    >>> i_hate_fives(10)
    Buzz!
    1
    2
    3
    4
    Buzz!
    6
    7
    8
    9
    """
    def buzz(m):
        i = 0
        while i < m:
            if i % n == 0:
                print('Buzz!')
            else:
                print(i)
            i += 1
    return buzz

Use OK to test your code:

python3 ok -q make_buzzer

Question 3: Count van Count

Consider the following implementations of count_factors and count_primes:

def count_factors(n):
    """Return the number of positive factors that n has."""
    i, count = 1, 0
    while i <= n:
        if n % i == 0:
            count += 1
        i += 1
    return count

def count_primes(n):
    """Return the number of prime numbers up to and including n."""
    i, count = 1, 0
    while i <= n:
        if is_prime(i):
            count += 1
        i += 1
    return count

def is_prime(n):
    return count_factors(n) == 2 # only factors are 1 and n

The implementations look quite similar! Generalize this logic by writing a function count_cond, which takes in a two-argument predicate function condition(n, i). count_cond returns a count of all the numbers from 1 to n that satisfy condition.

Note: A predicate function is a function that returns a boolean (True or False).

def count_cond(condition, n):
    """
    >>> def divisible(n, i):
    ...     return n % i == 0
    >>> count_cond(divisible, 2) # 1, 2
    2
    >>> count_cond(divisible, 4) # 1, 2, 4
    3
    >>> count_cond(divisible, 12) # 1, 2, 3, 4, 6, 12
    6

    >>> def is_prime(n, i):
    ...     return count_cond(divisible, i) == 2
    >>> count_cond(is_prime, 2) # 2
    1
    >>> count_cond(is_prime, 3) # 2, 3
    2
    >>> count_cond(is_prime, 4) # 2, 3
    2
    >>> count_cond(is_prime, 5) # 2, 3, 5
    3
    >>> count_cond(is_prime, 20) # 2, 3, 5, 7, 11, 13, 17, 19
    8
    """
    i, count = 1, 0
    while i <= n:
        if condition(n, i):
            count += 1
        i += 1
    return count

Use OK to test your code:

python3 ok -q count_cond

Question 4: Match and Apply

Sometimes when we are given a dataset, we need to alter it for specific values. For example, say we have a table with one column being people's names and the other being the price they have to pay.

We can use a list of pairs for this:

[["Jessica", 5], ["Andrew", 9], ["Alex", 2], ["Amir", 11], ["John", 3], ["Lyric", 2]]

The first value in each pair is the name, the second is the price.

Now, let's say we want to give a discount to specific people. We have a discount function that we want to apply to the person's price. Now, we need a function that will only apply the discount function to specific people.

Implement match_and_apply(pairs, function):

  • pairs is a list of pairs.
  • function is some function

match_and_apply returns a function such that when the function is given an input that matches the first of a pair, returns the result of applying function to the second value in the pair.

def match_and_apply(pairs, function):
    """
    >>> pairs = [[1, 2], [3, 4], [5, 6], [7, 8], [9, 0]]
    >>> def square(num):
    ...     return num**2
    >>> func = match_and_apply(pairs, square)
    >>> result = func(3)
    >>> result
    16
    >>> result = func(1)
    >>> result
    4
    >>> result = func(7)
    >>> result
    64
    >>> result = func(15)
    >>> print(result)
    None

    """
    def foo(num):
        for pair in pairs:
            if pair[0] == num:
                return function(pair[1])
        return None
    return foo

Use OK to test your code:

python3 ok -q match_and_apply