Assignment 9 Objects and Object Oriented Programming

CMPT 145

Principles of Computer Science
Assignment 9
Objects and Object Oriented Programming
Date Due: August 2, 2019, 11pm Total Marks: 65
General Instructions

• Each question indicates what to hand in. You must give your document the name we prescribe
for each question, usually in the form aNqM, meaning Assignment N, Question M.
• Make sure your name and student number appear at the top of every document you hand in.
These conventions assist the markers in their work. Failure to follow these conventions will result
in needless e?ort by the markers, and a deduction of grades for you.
• Do not submit folders, or zip ?les, even if you think it will help.
• Programs must be written in Python 3.

Question 0 (5 points):
Purpose: To force the use of Version Control in Assignment 9
Degree of Di?culty: Easy
You are expected to practice using Version Control for Assignment 9. This is a tool that you need to be
required to use, even when you don’t need it, so that when you do need it, you are already familiar with it.
Do the following steps.
1. Create a new PyCharm project for Assignment 9.
2. Use Enable Version Control Integration... to initialize Git for your project.
3. Download the Python and text ?les provided for you with the Assignment, and add them to your
project.
4. Before you do any coding or start any other questions, make an initial commit.
5. As you work on each question, use Version Control frequently at various times when you have implemented an initial design, ?xed a bug, completed a question, or want to try something di?erent. Make
your most professional attempt to use the software appropriately.
6. When you are ?nished your assignment, open the terminal in your Assignment 9 project folder, and
enter the command: git --no-pager log (double dash before the word ’no’). The easiest way to do
this is to use PyCharm, locate PyCharm’s Terminal panel at the bottom of the PyCharm window, and
type your command-line work there.
Note: You might have trouble with this if you are using Windows. Hopefully you are using the department’s network ?lesystem to store your ?les. If so, you can log into a non-Windows computer (Linux or
Mac) and do this. Just open a command-line, cd to your A6 folder, and run git --no-pager log there.
If you did all your work in this folder, git will be able to see it even if you did your work on Windows.
Git’s information is out of sight, but in your folder.
Note: If you are working at home onWindows, Google for how to make git available on your commandline window. You basically have to tell the command-line app where the git app is.
You may need to work in the lab for this; Git is installed there.
What to Hand In
After completing and submitting your work, open a command-line window in your Assignment 9 project
folder. Run the following command in the terminal: git --no-pager log (double dash before the word
’no’). Git will output the full contents of your interactions with Git in the console. Copy/paste this into a text
?le named a9-git.log.
If you are working on several di?erent computers, you may copy/paste output from all of them, and submit
them as a single ?le. It’s not the way to use git, but it is the way students work on assignments.
Be sure to include your name, NSID, student number, course number and laboratory section at the top of
all documents.
Evaluation
• 5 marks: The log ?le shows that you used Git as part of your work for Assignment 9. For full marks,
your log ?le contains
– Meaningful commit messages.
– At least three commits per question for a minimum number of 12 commits
Page 2
Department of Computer Science
176 Thorvaldson Building
110 Science Place, Saskatoon, SK, S7N 5C9, Canada
Telephine: (306) 966-4886, Facimile: (306) 966-4884
CMPT 145
Summer-Spring 2019
Principles of Computer Science
Question 1 (25 points):
Purpose: To adapt existing ADTs into the object-oriented paradigm.
Degree of Di?culty: Moderate
In class, we discussed how many of the ADTs we previously implemented could be equivalently represented using object-oriented programming. For this question you are going to implement object-oriented
versions of the node-based Stack and Queue ADTs (provided). You have been provided the following ?les
on moodle:
• NStack.py: A node-based Stack ADT.
• NQueue.py: A node-based Queue ADT.
• Node.py: A object-oriented node
• test_stack.py: A test script that can be used for testing your object-oriented Stack implementation.
• test_queue.py: A test script that can be used for testing your object-oriented Queue implementation.
To succeed in this question you will need to complete the following tasks:
(a) (10 points) Transcribe the node-based Stack ADT (NStack.py) into OO-style. Follow the object-oriented
guidelines described in Chapters 20 and 21 of the textbook. You are expected to write proper docstrings (interfaces) for each method. Use the provided test script to check the correctness of your
solution. Put your solution in a ?le called a9q1_Stack.py.
(b) (10 points) Transcribe the node-based Queue ADT (NQueue.py) into OO-style. Follow the object-oriented
guidelines described in Chapters 20 and 21 of the textbook. You are expected to write proper docstrings (interfaces) for each method. Use the provided test script to check the correctness of your
solution. Put your solution in a ?le called a9q1_Queue.py.
(c) (5 points) In a ?le call a9q1_reflection.txt, Answer the following questions about your experience
implementing these classes. You may use point form, and informal language. Just comment on your
perceptions; you do not have to give really deep answers. Be brief. These are not deep questions; a
couple of sentences or so ought to do it.
1. List the similarities between the two classes in terms of attributes and methods.
2. List the di?erences between the two classes in terms of attributes and methods.
3. Brie?y discuss some of the di?culties and/or errors you encountered when implementing and
debugging your classes. Did the similarity between the two classes help or hinder?
What to Hand In
• A ?le titled a9q1_Stack.py with your implemented OO-Stack class.
• A ?le titled a9q1_Queue.py with your implemented OO-Queue class.
• A ?le titled a9q1_reflection.txt.
Be sure to include your name, NSID, student number, course number and laboratory section at the top of
all documents.
Evaluation
• Stack Class
– 8 marks for implementation
– 2 marks for documentation
Page 3
Department of Computer Science
176 Thorvaldson Building
110 Science Place, Saskatoon, SK, S7N 5C9, Canada
Telephine: (306) 966-4886, Facimile: (306) 966-4884
CMPT 145
Summer-Spring 2019
Principles of Computer Science
• Queue Class
– 8 marks for implementation
– 2 marks for documentation
• Re?ection
– 2 marks for correctly identifying similar attributes and methods
– 2 marks for correctly identifying the distinct attributes and methods
– 1 mark for a discussion on encountered di?culties
Page 4
Department of Computer Science
176 Thorvaldson Building
110 Science Place, Saskatoon, SK, S7N 5C9, Canada
Telephine: (306) 966-4886, Facimile: (306) 966-4884
CMPT 145
Summer-Spring 2019
Principles of Computer Science
Question 2 (20 points):
Purpose: To practise inheritance.
Degree of Di?culty: Moderate
For this question, rewrite the object-oriented Stack and Queue code from the previous question using
inheritance to encapsulate common attributes and methods. You are expected to write proper doc-strings
(interfaces) for each method.
To succeed in this question you will need to complete the following tasks:
(a) (10 points) Implement a super-class called Container. This class should contain all the attributes and
methods common to the object-oriented Stack and Queue classes you identi?ed in the previous question. Put your solution in a ?le called a9q2_Container.py. Some of your original attributes and methods
may have to be changed to make them more generalizable.
(b) (5 points) Rewrite the object-oriented Stack class so that it inherits all the Container attributes and
methods. Put your solution in a ?le called a9q2_Stack.py. You can use the test script provided in
question 1 to make sure your new Stack class works correctly.
(c) (5 points) Rewrite the object-oriented Queue class so that it inherits all the Container attributes and
methods. Put your solution in a ?le called a9q2_Queue.py. You can use the test script provided in
question 1 to make sure your new Queue class works correctly.
What to Hand In
• A ?le titled a9q2_Container.py
• A ?le titled a9q2_Stack.py
• A ?le titled a9q2_Queue.py.
Be sure to include your name, NSID, student number, course number and laboratory section at the top of
all documents.
Evaluation
• Container Class
– 7 marks for implementation
– 3 marks for documentation
• Stack Class
– 1 marks for correctly setting up inheritance
– 3 marks for __init__()
– 1 mark for documentation
• Queue Class
– 1 marks for correctly setting up inheritance
– 3 marks for __init__()
– 1 mark for documentation
Page 5
Department of Computer Science
176 Thorvaldson Building
110 Science Place, Saskatoon, SK, S7N 5C9, Canada
Telephine: (306) 966-4886, Facimile: (306) 966-4884
CMPT 145
Summer-Spring 2019
Principles of Computer Science
Question 3 (15 points):
Purpose: To do a bit of Object Oriented Programming.
Degree of Di?culty: Moderate. The only problem is the time it will take to study and ?nd your way around
the given code base.
In this question we will be working with 2 object-oriented classes, and objects instantiated from them, to
build a tiny mock-up of an application that a teacher might use to store information about student grades.
Obtain the ?le a9q3.py from Moodle, and read it carefully. It de?nes two classes:
• GradeItem: A grade item is anything a course uses in a grading scheme, like a test or an assignment.
It has a score, which is assessed by an instructor, and a maximum value, set by the instructor, and a
weight, which de?nes how much the item counts towards a ?nal grade.
• StudentRecord: A record of a student’s identity, and includes the student’s grade items.
At the end of the ?le is a script that reads a text-?le, and displays some information to the console. Right
now, since the program is incomplete, the script gives very low course grades for the students. That’s
because the assignment grades and ?nal exam grades are not being used in the calculations.
Complete each of the following tasks:
1. Add an attribute called final_exam. Its initial value should be None.
2. Add an attribute called assignments. Its initial value should be an empty list.
3. Change the method StudentRecord.display() so that it displays all the grade items, including the
assignments and the ?nal exam, which you added.
4. Change the method StudentRecord.calculate() so that it includes all the grade items, including the
assignments and the ?nal exam, which you added.
5. Add a method called drop_lowest(grades) to StudentRecord that will search through the given list of
grade items, and sets its the weight to zero (not the score). The argument to this method, grades, is
any list of grade items, but should work for either the studnet’s lab marks or the student’s assignment
marks. The script at the end of the a9q3.py shows how it is applied to the students lab marks. Right
now, it does nothing!
6. Add some Python code to the end of the script to calculate a class average.
Additional information
The text-?le students.txt is also given on Moodle. It has a very speci?c order for the data. The ?rst two
lines of the ?le are information about the course. The ?rst line indicates what each grade item is out of
(the maximum possible score), and the second line indicates the weights of each grade item (according to
a grading scheme). The weights should sum to 100. After the ?rst two lines, there are a number of lines,
one for each student in the class. Each line shows the student’s record during the course: 10 lab marks,
10 assignment marks, followed by the midterm mark and the ?nal exam mark. Note that the marks on a
student line are scores out of the maximum possible for that item; they are not percentages!
The function read_student_record_file(filename) reads students.txt and creates a list of StudentRecords.
You will have to add a few lines to this function to get the data into the student records. You will not have
to modify the part of the code that reads the ?le.
List of ?les on Moodle for this question
• a9q3.py — partially completed
• students.txt
Page 6
Department of Computer Science
176 Thorvaldson Building
110 Science Place, Saskatoon, SK, S7N 5C9, Canada
Telephine: (306) 966-4886, Facimile: (306) 966-4884
CMPT 145
Summer-Spring 2019
Principles of Computer Science
What to Hand In
• The completed ?le a9q3.py.
Be sure to include your name, NSID, student number, course number and laboratory section at the top of
the ?le.
Evaluation
• 1 mark: You correctly added the attribute final_exam to StudentRecord
• 1 mark: You correctly added the attribute assignments to StudentRecord
• 3 marks: You correctly modi?ed StudentRecord.display() correctly to display the new grade items.
• 3 marks: You correctly modi?ed StudentRecord.calculate() correctly to calculate the course grade
using the new grade items.
• 5 marks: You correctly added a method called drop_lowest() to StudentRecord class. Your function
is correct, and e?cient, and demonstrates good design.
• 2 marks: You added some code to the script that calculates the class average.
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