Due at 11:59:59 pm on Thursday, 10/3/2019.

## 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. See this article for more instructions on okpy and submitting assignments.

Readings: This homework relies on following references:

## 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]

"""
``````

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
"""
``````

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
"""
``````

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

"""
``python3 ok -q match_and_apply``