CSCA08H Assignment 1
Deadline: Tuesday October 1 2019 by 4:00pm Wednesday Oct 2 2019 at 6:00 p.m.
(to accommodate those of us attending the Global Climate Strike)
Late policy: There are penalties for submitting the assignment after the due date.
These penalties depend on how many hours late your submission is. Please see the
course website for more information.
Goals of this Assignment
Use the Function Design Recipe to plan, implement, and test functions.
Write function bodies using variables, numeric types, strings, and conditional
statements. (You can do this whole assignment with only the concepts from
Weeks 1, 2, and 3 of the course.)
Learn to use Python 3, Wing 101, provided starter code, a checker module, and
other tools.
Tweet Analyser
This assignment is based on the social network company Twitter. Twitter allows users
to read and post tweets that are between 1 and 280 characters long, inclusive. In this
assignment, you will be writing functions that (we imagine) are part of the programs
that manage Twitter feeds.
Here are some example tweets:
Standing ovation as Setsuko Thurlow ​ is awarded a Doctor of Laws degree, honoris
causa, by the University of Toronto @UofT for her tireless nuclear disarmament work
and contributions to the Treaty on the Prohibition of Nuclear Weapons with
@nuclearban ICAN
Congratulations to our class of 2019 #UofTGrad19
#UofT's @ProbabilityProf @UofTStatSci created a mathematical model at the start of
the playoffs to figure out the team's odds of winning. He predicts their home-court
advantage will give them an edge. http://bit.ly/ProbProf
Some terminology
We will use the following terms in this assignment.
tweet: A message posted on Twitter. For our assignment, a valid tweet is
between 1 and MAX_TWEET_LENGTH characters long (inclusive). MAX_TWEET_LENGTH is a
constant.
tweet word: A word in a tweet. For our assignment, a valid tweet word contains
only alphanumeric characters and underscores. For example, pink_elephant is a
valid tweet word, while bits&pieces is not (In fact, bits&pieces has two valid tweet
words, bits and pieces, with an ampersand (&) between them.)
hashtag: A word in a tweet that begins with the hash symbol. Twitter uses the
number sign (#) as the hash symbol. For our assignment, we'll use the constant
HASHTAG_SYMBOL to represent the hash symbol. Hashtags are used to label important
words or terms in a tweet. A valid hashtag has the hash symbol as its first
character and the rest of the characters form a valid tweet word. In other words,
a hashtag begins with the hash symbol, and contains all alphanumeric characters
and underscores up to (but not including) the first non-alphanumeric character
(such as space, punctuation, etc.) or the end of the tweet. A hashtag must
contain at least one alphanumeric character.
#UofT, #cscA08, and #Go_Raptors are three examples of hashtags on Twitter.
Note that a hashtag is not a valid tweet word, because it has the hash symbol as
its first character.
mention: A word in a tweet that begins with the mention symbol. Twitter uses
the at-sign (@) as the mention symbol. For our assignment, we'll use the constant
MENTION_SYMBOL to represent the mention symbol. Mentions are used to direct a
message at or about a particular Twitter user, so the word should be a Twitter
username (but for the purposes of this assignment, we will not check if the word
that follows the MENTION_SYMBOL is a real username — we'll just assume it). For our
purposes, the definition of a mention is very similar to that of a hashtag. A valid
mention has the mention symbol as its first character and the rest of the
characters form a valid tweet word. In other words, a mention begins with the at-
sign, and contains all alphanumeric characters and underscores up to (but not
including) the first non-alphanumeric character (such as space, punctuation, etc.)
or the end of the tweet. A mention must contain at least one alphanumeric
character.
@redcrosscanada, @UN_Women, and @UofTGrad2019 are three examples of Twitter
mentions.
Note that a mention is not a valid tweet word, because it has the mention symbol
as its first character.
Here are some more interesting examples of how we will treat valid tweet words,
hashtags, and mentions in this assignment.
In the tweet
Raptors win championship,#NBAFINALS, Go @Raptors!!! #WeTheNorth
we have four valid tweet words (Raptors, win, championship, and Go), two hashtags
(#NBAFINALS and #WeTheNorth), and one mention (@Raptors). It is important to note
that in this example there is no space between the first comma and the hashtag
#NBAFINALS, there is a comma immediately following the hashtag #NBAFINALS, there
are three exclamation marks immediately following the mention @Raptors, and
there are more than one space after the exclamation marks. All these are valid in
a tweet. Also note that the first occurrence of the word Raptors is not considered
to be a mention, because it does not have the mention symbol.
In the tweet
@UofT welcomes its 2019 graduates! #UofTGrad2019#graduation!
we have four valid tweet words (welcomes, its, 2019, and graduates), two hashtags
(#UofTGrad2019 and #graduation), and one mention (@UofT). It is important to note
that in this example there is no space between hashtags #UofTGrad2019 and
#graduation. This is also valid in a tweet.
Some more obscure yet valid examples:
In something#something_else we consider something is a valid tweet word and
#something_else is a hashtag.
In no@spaces#whatsoever?! we consider no is a tweet word, @spaces is a mention,
and #whatsoever is a hashtag.
For a complete list of Twitter terms, check out the Twitter glossary.
Starter code
For this assignment, we are giving you some files, including a Python starter code
files. Please download the Assignment 1 Files and extract the zip archive.
Starter code: tweet.py
This file contains some constants, the header and the complete docstring (but not
body) for the first function you are to write. Your job is to complete this file.
Checker: a1_checker.py
We have provided a checker program that you should use to check your code.
See below for more information about a1_checker.py.
Constants
Constants are special variables whose values do not change once assigned. A different
naming convention (uppercase pothole) is used for constants, so that programmers
know to not change their values. For example, in the starter code, the constant
MAX_TWEET_LENGTH is assigned the value 50 at the beginning of the module and the value
of MAX_TWEET_LENGTH should never change in your code. When writing your code, if you
need to use the value of the maximum tweet length, you should use MAX_TWEET_LENGTH.
The same goes for the other constant values.
Using constants simplifies code modifications and improves readability. If we later
decide to use a different tweet length, we would only have to change the length in one
place (the MAX_TWEET_LENGTH assignment statement), rather than throughout the
program.
What to do
In the starter code file tweet.py, complete the following function definitions. Use the
Function Design Recipe that you have been learning in this course . We have included
the type contracts in the following table; please read through the table to understand
how the functions will be used.
We will be evaluating your docstrings in addition to your code. Please include two
examples in your docstrings. You will need to paraphrase the full descriptions of the
functions to get an appropriate docstring description.
Function name:
(Parameter types)
-> Return type
Full Description (paraphrase to get a proper docstring
description)
is_valid_tweet:
(str) -> bool
The parameter represents a potential tweet. The function
should return True if and only if the tweet contains between 1
and MAX_TWEET_LENGTH characters, inclusive.
compare_tweet_lengths:
(str, str) -> int
The two parameters represent valid tweets. This function must
return one of three integers: 1 (if the first tweet is longer than
the second), -1 (if the second tweet is longer than the first), or
0 (if the tweets have the same length).
add_hashtag:
(str, str) -> str
The first parameter represents a valid tweet. The second
parameter represents a valid tweet word.
Appending a space, a hash symbol, and the tweet word to the
end of the original tweet will result in a potential tweet. If the
potential tweet is a valid tweet, the function should return the
potential tweet. If the potential tweet is not a valid tweet, the
function should return the original tweet.
For example (assuming the hash symbol is '#'), if the first
argument is 'I like' and the second argument is 'cscA08', then
the function should return 'I like #cscA08', if
MAX_TWEET_LENGTH is at least 14. Otherwise, it should return
'I like'.
The first parameter represents a valid tweet, and the second
parameter represents a valid tweet word. This function should
return True if and only if the tweet contains a hashtag made up
contains_hashtag:
(str, str) -> bool
of the hash symbol and the tweet word. For example (assuming
the hash symbol is '#'), if the first argument is 'I like #cscA08',
and the second argument is 'cscA08', then the function should
return True.
Notes: If the first argument is 'I like #cscA08', and the second
argument is 'csc', then the function should return False. Also, if
the first argument is 'I like #cscA08, #mat137, and #phl101', and
the second argument is cscA08, the function should return True.
Hint: Use the helper function clean that is provided in the
starter code.
is_mentioned:
(str, str) -> bool
The first parameter represents a valid tweet, and the second
parameter represents a valid tweet word. This function should
return True if and only if the tweet contains a mention made up
of the mention symbol and the tweet word. For example
(assuming the mention symbol is '@'), if the first argument is
'Go @Raptors!', and the second argument is 'Raptors', then the
function should return True.
Hint: This function is very similar to the function
contains_hashtag. What can you do to avoid writing the same
code twice?
add_mention_exclusive:
(str, str) -> str
The first parameter represents a valid tweet and the second
parameter represents a valid tweet word. Appending a space, a
mention symbol, and the tweet word to the end of the original
tweet will result in a potential tweet. If the potential tweet is
valid and the original tweet contains the given tweet word, the
function should return the potential tweet. In all other cases,
the function should return the original tweet. Note that if the
tweet word is mentioned in the original tweet (i.e., it appears
with a MENTION_SYMBOL as a first character), then the
function should return the original tweet.
For example (assuming the mention symbol is '@'), if the first
argument is 'Go Raptors!' and the second argument is 'Raptors',
then the function should return 'Go Raptors! @Raptors'. If, on the
other hand, the first argument is 'Go @Raptors!' and the second
argument is 'Raptors', then the function should return the
original tweet 'Go @Raptors!'.
Hint: Can you use one of your other functions as a helper
function?
The parameter represents a message. This function should
return the minimum number of tweets that would be required
Functions to write for A1
num_tweets_required:
(str) -> int
to communicate the entire message. Recall the maximum
length of a tweet is MAX_TWEET_LENGTH.
Hint: The ceil function in the math module is useful here.
get_nth_tweet:
(str, int) -> str
The first parameter represents a message that a Twitter user
would like to post, and the second parameter, n, represents an
integer greater than or equal to 0. If the message contains too
many characters, it would need to be split up into a sequence
of tweets. All of the tweets in the sequence, except possibly the
last tweet, would be of length MAX_TWEET_LENGTH. This function
should return the nth valid tweet in the sequence of tweets.
Note that the first tweet in the sequence has index 0, the
second tweet in the sequence has index 1, and so on. If the
value of the second parameter is too large, so there is no
index-n tweet in the sequence, this function should return an
empty string.
Using Constants
As we discuss in section Constants above, your code should make use of the provided
constants. If the value of one of those constants were changed, and your program
rerun, your functions should work with those new values.
For example, if MAX_TWEET_LENGTH were changed, then your functions should work
according to the new maximum tweet length.
Your docstring examples should reflect the given values of the constants in the
provided starter code, and do not need to change.
No Input or Output
Your tweet.py file should contain the starter code, plus the function definitions specified
above. tweet.py must not include any calls to the print and input functions. Do not add
any import statements. Also, do not include any function calls or other code outside of
the function definitions.
How should you test whether your code works
First, run the checker and review ALL output — you may need to scroll. You should
also test each function individually by writing code to verify your functions in the
Python shell. For example, after defining function compare_tweet_lengths, you might call
it from the shell (e.g., compare_tweet_lengths('I love', 'programming')) to check whether
it returns the right value (-1). One call usually isn't enough to thoroughly test the
function — for example, we should also test compare_tweet_lengths('programming', 'is
fun') where it should return 1 and compare_tweet_lengths('this course', 'is for me!!')
where it should return 0.
A1 Checker
We are providing a checker module a1_checker.py that tests two things:
whether your code follows the Python style guidelines, and
whether your functions are named correctly, have the correct number of
parameters, and return the correct types.
To run the checker, open a1_checker.py and run it. Note: the checker file should be in
the same directory as your tweet.py, as provided in the starter code zip file. We have
posted a demo of the checker being run and included it in the Week 3 Prepare
exercises on PCRS. Be sure to scroll up to the top and read all messages.
If the checker passes for both style and types:
Your code follows the style guidelines.
Your function names, number of parameters, and return types match the
assignment specification. This does not mean that your code works
correctly in all situations. We will run a different set of tests on your code once
you hand it in, so be sure to thoroughly test your code yourself before
submitting.
If the checker fails, carefully read the message provided:
It may have failed because your code did not follow the style guidelines. Review
the error description(s) and fix the code style. Please see the PyTA documentation
for more information about errors.
It may have failed because:
you are missing one or more functions,
one or more of your functions is misnamed,
one or more of your functions has the incorrect number or type of
parameters, or
one of more of your function return types does not match the assignment
specification.
Read the error message to identify the problematic function, review the function
specification in the handout, and fix your code.
Make sure the checker passes before submitting.
Marking
These are the aspects of your work that may be marked for A1:
Coding style (20%):
Make sure that you follow Python style guidelines that we have introduced
and the Python coding conventions that we have been using throughout the
semester. Although we don't provide an exhaustive list of style rules, the
checker tests for style are complete, so if your code passes the checker, then
it will earn full marks for coding style with one exception: docstrings may be
evaluated separately. For each occurrence of a PyTA error, one mark (out of
20) deduction will be applied. For example, if a C0301 (line-too-long) error
occurs 3 times, then 3 marks will be deducted.
All functions, including helper functions, should have complete docstrings
including preconditions when you think they are necessary.
Correctness (80%): Your functions should perform as specified. Correctness, as
measured by our tests, will count for the largest single portion of your marks.
Once your assignment is submitted, we will run additional tests not provided in
the checker. Passing the checker does not mean that your code will earn full
marks for correctness.
No Remark Requests
No remark requests will be accepted. A syntax error could result in a grade of 0 on the
assignment. Before the deadline, you are responsible for running your code and the
checker program to identify and resolve any errors that will prevent our tests from
running.
What to Hand In
The very last thing you do before submitting should be to run the checker
program one last time.
Otherwise, you could make a small error in your final changes before submitting that
causes your code to receive zero for correctness.
Submit tweet.py on MarkUs by following the instructions on the course website.
Remember that spelling of filenames, including case, counts: your file must be named
exactly as above.