CSC108H5S Winter 2022, Assignment 3
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CSC108H5S Winter 2022,
Assignment 3
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.
Sets have no order. There are no indices and you can’t access individual elements.
Checking whether a value is in a set is instantaneous, no matter the size.
Sets have their own set of operations as described in set theory. You may find set union and set difference useful and, in general, you will find sets a valuable tool throughout this assignment.
Important Reminders
Compared to prior assignments, note this time that we are asking you to write functions that do what we have specified. In particular, none of your functions should use input or print.
Please don’t change what you have been given in the starter code. If you do, then our correctness tests on your code will not work correctly.
For the code we have given you, do not add or remove any parameters,
change any parameters or return types, or change any type annotations. Please don’t add additional import statements.
You can and should add helper functions to keep your code organized. Test, test, test! The test cases that we give you are not to be considered full testing.
Please submit all of your files to MarkUs.
You must work alone on this assignment.
The final thing you should do is to open your code files in Notepad and make sure that the code displays correctly as only Python code.
2022-04-11