Q1: Finding the Key

Background

It has been rumored that professor Dan has a reading level of a 5 year old. Being embarrassed of this, he keeps his books encrypted so that others cannot find out what he is reading. You somehow stumble into his book library and discover the encrypted books. Since you took a class with Dan, you want to discover if the       rumour is true.

We define the encrypted text as the text that is encrypted and therefore not currently readable. We define the plaintext as the text that was encrypted.

Remember the Caesar Cipher that we worked on in Week 3? After some                  investigation, you realize that Dan has used a Caesar Cipher to encrypt each book.

As a reminder, Caesar Cipher is an encryption technique in which each letter of  the plaintext is shifted by a certain number of characters. The encrypted text can be decrypted by shifting in the opposite direction.

In Week 3, we used a shift value of 3. Here, Dan has chosen his own shift value for each book.

You need to decrypt Dan’s books to figure out what he is reading and confirm/deny the rumour.

You will write a function that can be used to decrypt Dan’s encrypted text. You     will be given an openfile that contains an encrypted passage from one of the         books, and the name of afile containing a wordlist of English words. You need to discover the shift value to use (0-25) in order to decrypt the text. A correct shift   value is one that leads to the maximum number of words being found in the          English list of words.

To find the words in the encrypted text, you must call split(). For a given shift   value, convert all letters to lowercase, then try to find each word in the English     wordlist. Do not remove any punctuation or symbols from the word: for example, if the word is hello!, then that is the exact string, including exclamation mark,    that you should try to find in the English wordlist.

Your function should return a string where all letters are in lowercase, and all other characters (newlines, spaces, punctuation, etc.) are retained.

Input

In each test case, we will call your decrypt function with an openfile that         contains encrypted text, and the name of afile containing an English wordlist.

An encrypted file contains the encrypted text; for example, it might look like this:

Q svme pm nmtb smmvtg bpm ijamvkm wn pqa

wev niuqtg.

An English wordlist has one word per line; here is a small example:

abases

abash

abashed

abashes

abashing

abashment

Return Value

Using the full English wordlist provided in the starter code, your function would return the following string for the above encrypted text:

i knew he felt keenly the absence of his

own family.

Starter code

Please find your starter code and test examples in MarkUs.

In decrypt.py, you’ll find a function named decrypt whose implementation you must complete.

Testing

We have a thorough set of tests on which we’ll run your code. Everything we’ll       test has been discussed here and in the starter code, so please read both carefully!

The starter code includes the test case from this handout that you can try out by running test_decrypt.py. We have also provided several txt files that you can use to test as well.

Q2: A Bard Day’s Night

Background

Once upon a time, in a certain medieval village, a group of mysterious strangers appeared in jeans and T-shirts. The strangers managed to learn enough Old       English to explain that they had been enjoying their favourite pastime – belting out tunes at a karaoke party – when they saw a blinding flash and heard a           thunderous roar, lost consciousness, and found themselves transported back in time without any explanation.

Of all their bizarre story, the villagers were most interested in the strangers’ wide- ranging knowledge of popular songs from their own time. They understood that    the strangers belonged to some sort of bard class. The villagers were also party      animals, and had a feast every night. The bards agreed to come to some of the       parties and sing one Billboard Top 40 song whenever they did. When they              weren’t there, the villagers would sing these songs to each other, reverently,           knowing that they held clues to the future of their world. The more they learned,  the more they were able to share, and some were even initiated into the                   mysterious strangers’ inner circle and allowed to become bards and learn all the   secrets of the 21st-century pop music scene. The village chronicler wrote down      the most important things they learned from these portentous events.

Simulate the above village with its nightly parties.

You’ll be given a list of villagers and bards. You’ll also get a list of songs. The bards start out knowing every song, but no one else knows any songs.

You’ll be given a list of parties with their attendees, in the order that the parties are held. Every party features singing. There are two ways a party can unfold:

If there’s at least one bard present, they sing a song that none of the regular    villagers at the party know yet. (Specifically, the first new song alphabetically, according to Python’s sort order of strings.)

If there are no bards present, everyone at the party sings all the songs they

know at that point.

Either way, whenever a song is sung, everyone at the party learns and remembers it.

If a villager learns enough songs, and they’re at a party with a bard, they too become a bard and learn every song.

Finally, you’ll calculate some statistics about the simulation.

Technical details

Input

Each test case is one input file. Here’s a sample input file:

VILLAGERS

Luke Sawczak

Dan Zingaro*

Freddie Prinze Jr.

Arnold Rosenbloom

SONGS

People, I 've Been Sad

Call Me Maybe

What a Man Gotta Do

Delete Forever

PARTIES

Dan Zingaro,Freddie Prinze Jr.,Arnold Rosenbloom

Arnold Rosenbloom,Luke Sawczak,Freddie Prinze Jr.

Dan Zingaro,Luke Sawczak

Freddie Prinze Jr.,Luke Sawczak,Arnold Rosenbloom

Villagers with an asterisk * after their name are bards. However, the asterisk isn’t part of their name – notice there are no asterisks in the party list.

Of course, there may be any number of villagers, bards, songs, and parties.

Walkthrough of the above example

The first party has a bard, Dan. He sings Call Me Maybe (the first alphabetical       song that no one knows). At the next party, there’s no bard, but Arnold and            Freddie teach Call Me Maybe to Luke. At the third party, Dan the bard is back.      Since Luke already knows Call Me Maybe, Dan debuts Delete Forever next. At the fourth party, Luke teaches Freddie and Arnold Delete Forever. If the threshold to become a bard was 2, Luke would have qualified to be a bard after the third party, and Freddie and Arnold after the fourth party.

Statistics

After the simulation, you will prepare and return these stats on your village’s parties:

1. unheard_songs: The set of songs that have never been heard by non-bards.

2. billboard_top: A list of the n best-known songs in descending order from songs known by the most people to songs known by the fewest. Break ties alphabetically, according to Python’s sort order of strings.

3. all_bards: The set of villagers who are bards, whether they started out as one or became one by learning enough songs.

4. average_attendees: The average number of people at a party. Round up to the nearest integer (so both 1.7 and 1.1 should become 2).

Starter code

Please find your starter code and test examples in MarkUs.

In bard.py, you’ll find functions marked with TODO whose implementations you must complete.

You also have a couple of import statements to make the type annotations work    and constants for the number of songs a villager must know to become a bard and the number of Billboard Top songs.

Take some time to read over the starter code to understand the structure, as well as the functions you’ve been given and the functions you must write.

We have a thorough set of tests on which we’ll run your code. Everything we’ll       test has been discussed here and in the starter code, so please read both carefully!

The starter code has some tests, including one holistic test (the statistics you should output for the sample given above), which you can try out by running test_bard.py.

F.A.Q.

Can there be duplicate villager names or song names?

No.

What happens if there are multiple bards at a party?

Only one of them sings. It doesn’t matter which one, since they would all choose the same next song.

What happens if there are only bards at a party?

Whether anyone sings or not makes no difference since all the bards already know all the songs.

What happens if there are no new songs for a bard to sing?

The party is boring. No one sings. Nothing changes.

What happens if a party has no bard, but during the party a villager learns enough songs to become one?

A villager can only become a bard at a party that already has a bard, so this can’t  happen. A party either has a bard at the beginning or doesn’t, and a party’s status never changes once it’s begun.

If there’s a party where a villager learns enough songs to become a bard but there isn’t a bard at the party, do they miss their chance?

No, they become a bard at the next party they attend where there’s a bard (if they ever attend such a party).

Sets

One of the concepts you’ll be practicing throughout this assignment is sets. A set is very much like a list, with a few differences:

There are no duplicate values in a set. No matter what you do, values are always unique.