Need Help with this Computer Science questions

Question

consider the following function named "mystery"

def mystery (slist):

d = {}

for w in slist:

n = len(w)

if n not in d:

d[n] = [w]

else:

d[n].append(w)

return d

Assume the mystery is called as follows:

mylist = ['the', 'cat', 'in', 'hat', 'ran', 'fast', 'telephone]

answer = mystery(mylist)

a. what do the keys in the dictionary stored in "answer" represent?

b. What value is associated with the key that is equal to "4" in the dictionary stored in "answer"?

Answer 1

Walk through what happens when this is called.

1. It iterates over the items in the list. The first item is "the"
2. It checks the length of the string. The first item is length 3
3. It adds the word in the dictionary with the key of the length, so after the first iteration it is:

{3: ["the"]}

So at the end it will be:

{

2: ["in"],

3: ["the", "cat", "hat", "ran"],

4: ["fast"],

9: ["telephone"],

}

So each key is the length of the words stored in the array in the dict for that value.

So then the value stored for 4 is:

["fast"]

Answer 2

Before answering these questions, first we need to understand what is a dictionary and how it works in Python?

A dictionary is a collection of key and value pairs. Below are some of the ways we can use a dictionary:

# initialize a dictionary

myDict = {}

# add a new key to a value in dict

myDict[new_key] = new_val

# access a value from a dictionary with a key

myDict[new_key] # return new_val

After getting that out of the way, let take a look at your questions.

a. what do the keys in the dictionary stored in "answer" represent?

--> That's great that you recognized "answer" is a dictionary. If you look at the function, mystery(), var "d" is the dictionary that is returned, hence it will be stored in answer.

My question to you is what keys are added to dictionary "d" in the function. Specifically, what does the 6th line do in the code " d[n] = [w]" ? (Hints: check the common usage of dict I provided above). What's "n" in d[n]? (Hints:n = len(w)) , what is len(w)?

b. This question is a followup question, once you get question "a", you should be able to answer this question.

I strongly recommend you using http://www.pythontutor.com to visualize your code. Good luck. Please leave a comment below if you still have questions.