Problem Set 1 - Due Tue, Sep 11 at 23:59

Reading

  1. The CS111 Problem Set Guide gives an overview of psets, including a detailed description of individual and partner tasks
  2. Lecture 01 slides and notebook
  3. Lab 01
  4. Lecture 02 slides and notebook
  5. Goldwasser & Letscher, Chapter 3, sections 3.1-3.2, pages 89-103
  6. Our CS 111 Code Style Guide describes rules for Python coding style that you should follow.

About this Problem Set

This problem set will give you practice with basic Python interactive programs as well as creating graphic scenes with the cs1graphics library.

  1. In Task 0, you will familiarize yourself with the course google group, cs111-fall18.

  2. Task 1 is an individual problem in which you will get practice with debugging in the context of fixing a misbehaving program.

  3. In Task 2, you will write a time profiler program that calculates and visualizes the time spent by a person per week on various activities.

  4. In Task 3 (Partner task), you will create a graphics scene using the cs1graphics package.

  5. Use this shared Google Doc to find and record your pair programming partner. Please DO NOT use the cs111-fall18 group to find partners. Remember, you can talk with other individuals and teams about high-level problem-solving strategies, but you cannot share any code with them.

  6. Read the PS01 FAQ -- it covers the most common issues students encounter when working on PS01.

  7. The CS111 Problem Set Guide gives an overview of psets, including a detailed description of individual and partner tasks.

  8. In previous semesters, cs111 students spent an average of GET THIS NUMBER hours on Task 1 (min = 1 hour, max = 9 hours), GET THIS NUMBER on Task 2 (min = 1 hour, max = 9 hours), and GET THIS NUMBER on Task 3 (min = 1 hour, max = 9 hours). [LYN THINKS WE SHOULD NOT LIST MINS AND MAXES, ONLY AVERAGES AND MEDIANS?]

All code for this assignment is available in the ps01 folder in the cs111/download directory within your cs server account, which you learned how to access in Lab 1.

Guidelines for checking the correctness and quality of your solution are here.


Task 0: Ask or answer a question on cs111-fall18

On a typical problem set, we expect that you will have many questions.

You can seek answers to these questions from instructors during office hours; from tutors during drop-in hours; from SI leaders during their sessions; and from fellow classmates.

Another important way to ask questions is to post them on the cs111-fall18 Google group. This forum is monitored by the CS111 staff and your classmates, one of whom will try to answer your question in a timely fashion. To get you in the habit of posting to and reading this group, we require that every student posts at least one question or one answer on the cs111-fall18 group in the first couple weeks of the semester.

When do I post my question or my answer?

Tips on posting to the course google group (cs111-fall18)

Tips on email inbox management

With more about 120 students in the cs111-fall18 group, your inbox will quickly fill with messages.

If you have difficulties talk to an instructor or tutor.


Task 1: Debugging Numbers

This is an individual problem which you must complete on your own, though you may ask for help from the CS111 staff.

Background

It is rarely the case that code works the first time you test it. It often contains one or more so-called bugs that cause it to behave incorrectly. So much of the time you spend programming in the course will involve debugging, which is the process of finding and removing bugs.

One of the themes of this course is learning strategies for debugging. So we will have some problem set problems that focus on debugging. This is the first such problem, but there will be others. In these problems you will be given code that does not work, and your goal will be to debug it until it does work.

Here's a simple example of a program that does not behave as expected:

  username = raw_input('What is your name? ') # line 1
  print 'Hello, username'                     # line 2
  n = raw_input('Enter an integer n: ')       # line 3
  print 'n is', n, '; 2*n is', 2*n            # line 4

For example:


What is your name? Wendy
Hello, username

Enter an integer n: 23
n is 23 ; 2*n is 2323

(Important Note: In this pset, we use magenta text to highlight text entered by the user to distinguish it from text printed by the program, which is in black. If you actually run the program, the text entered by the user will also appear in black; it will not be displayed in magenta.)

This program misbehaves in two ways:

  1. Rather than displaying the name (Wendy in this case) entered by the user, it always displays the string username.
  2. Rather than showing the double of the integer n for the expression 2*n (46 in this case) it shows the two-fold concatenation of the the digts in the number ("2323" in this case).

The first bug is due to the fact that in line 2, the occurrence of username inside the printed string denotes the literal string "username" and not the value of the variable named username. This can be fixed by changing line 2 to be

  print 'Hello, ' +  username        # fixed line 2, version 1, for 1st bug

or

  print 'Hello,', username           # fixed line 2, version 2, for 1st bug

The second bug occurs because in the expresion 2*n the value of n is the string of digits entered by the user (e.g., the 2-digit string "23") rather than the integer 23. This can be fixed by using the int() function to convert the string of digits "23" to the integer 23. One way to apply this fix is to change line 4 to be

  print 'n is', n, '; 2*n is', 2*int(n)      # fixed line 4 for 2nd bug

Alternatively, we could leave line 4 unchanged, and instead change line 3 to be

  n = int(raw_input('Enter an integer n: ')) # fixed line 3 for 2nd bug. 

With either combination of fixes, the program now works as expected:


What is your name? Wendy
Hello, Wendy

Enter an integer n: 23
n is 23 ; 2*n is 46

This example illustrates that (1) even a very short program can contain multiple bugs and (2) often there is more than one way to fix a bug.

A Note on print

Most examples involving print that you have seen in the course up to this point involve calling it with a single parenthesized argument that's a string. For example, suppose that:

Then:

print('i is ' + str(i) + '; f is ' + str(f) + '; s is ' + s)

displays the characters

i is 42; f is 6.023; s is bunny

However, it turns out that in Python 2.7 (the version we use), print is not really a function and it can be used in some ways that are both special and convenient. In particular,

For example:

print 'i is', i, '; f is', f, '; s is', s

will also displays the characters

i is 42; f is 6.023; s is bunny

Passing comma-separated values with arbitrary types to print is often more convenient that having to convert the values to strings and concatenating them into one big string.

The debugNumsBuggy.py Program

Bud Lojack is experimenting with a Python program that processes numbers entered by the user. He wants his program to behave as shown in the following examples, where text highlighted in magenta is entered by the user.

Sample Execution #1


Enter a nonnegative integer intNum: 17
The integer you entered is 17
Three times intNum is 51
17 concatenated copies of X is XXXXXXXXXXXXXXXXX
The integer remainder of 17 divided by 3 is 2
The integer quotient of 17 divided by 3 is 5
The floating point quotient of 17 divided by 3 is 5.66666666667
The number of digits in 17 is 2

Enter a floating point number floatNum: 143.816
floatNum is 143.816
143.816 rounded to two places is 143.82
143.816 truncated to an integer is 143
143.816 rounded to an integer is 144

The maximum of 17 and 143.816 is 143.816

Sample Execution #2


Enter a nonnegative integer intNum: 6
The integer you entered is 6
Three times intNum is 18
6 concatenated copies of X is XXXXXX
The integer remainder of 6 divided by 3 is 0
The integer quotient of 6 divided by 3 is 2
The floating point quotient of 6 divided by 3 is 2.0
The number of digits in 6 is 1

Enter a floating point number floatNum: 3.141
floatNum is 3.141
3.141 rounded to two places is 3.14
3.141 truncated to an integer is 3
3.141 rounded to an integer is 3

The maximum of 6 and 3.141 is 6

Click here to see Bud's program, which attempts to implement the above behavior. His progam can also be found in the ps01 folder in the file debugNumsBuggy.py.

Bud's program has numerous bugs that prevent it from working properly. Your goal in this subtask is to fix Bud's program so that it behaves as indicated by the above examples. In the ps01 folder is a file debugNumsFixed.py that initially is a copy of Bud's program with some additional header information at the top that you should fill out. You should modify debugNumsFixed.py by finding and fixing all the bugs it contains, so that ultimately it has the correct behavior. You should also explain the bugs and your fixes by defining string variables bug1, fix1, bug2, fix2, etc. as described below.

Notes:

# Below, summarize your bug fixes using variables named bug1, fix1, 
# bug2, fix2, etc. that are assigned to triple-quoted strings. 

bug1 = '''Line 2 prints the characters in the string "username" rather than 
          the value of the string stored in the variable named username'''

fix1 = '''Change the printed string to be the result  "Hello, " + username, 
          which concatenates the string "Hello, " with the string stored 
          in the variable username.'''

bug2 = '''Because the variable n holds a string and not an integer, 
          the expression 2*n in line 4 returns the result of concatenating 
          that string with itself.'''

fix2 = '''Change the expression 2*n in line 4 to 2*int(n), which uses int()
          to convert a string of digits to the corresponding integer.'''

Why should you use triple-quoted strings in these definitions? Because triple-quoted strings can have multiple lines, but strings delimited by only one pair of single or double quotes cannot.

Running Codder on Task 1

To test that your debugNumsFixed.py program works as expected, you can use the Codder code feedback tool you saw in Lab 01, Part 3 to test your program.

Codder is now available for testing your debugNumsFixed.py program. Follow these steps:
  1. Go to https://cs.wellesley.edu/codder
  2. Authenticate yourself with your Wellesley domain name and password (do not use your cs.wellesley.edu password!)
  3. From the drop-down menu, select ps01 as the activity.
  4. Click on the Choose file button, and use the pop-up file selection window to navigate to your debugNumsFixed.py file.
  5. Click on the submit file button.

The Codder server will take a few seconds to respond with feedback on your code.

In the resulting report, pay attention to the parts marked in light purple, which highlight potential problems with your program. You should try to fix the reported issues in your program, and resubmit. You can resubmit your code as many times as you want.


Task 2: Time Profiler

This is an individual problem which you must complete on your own, and may ask for help from the CS111 staff.

Armed with Python knowledge from your first CS111 lectures and lab, and confident with your debugging skills from Task 1, you've decided to form a software startup that provides your fellow students with useful programs.

Since time is important to all Wellesley students, you've decided your first program should be a time profiler that helps students visualize how they spend their time during a typical week. The program will ask the user to enter a few pieces of information, and then will display a textual representation of the hours they spend in four activities during the week:

  1. Classwork: This includes time in class plus homework time. You may assume in general that two hours of homework time are required for every hour in class.
  2. Activities Outside of Class: This includes time spent in organized athletics, music activities, and clubs, as well as any jobs. Your program will ask the user to name this category.
  3. Sleep: This is the amount of time you spend sleeping each week.
  4. Free Time: For simplicity, this category encompasses all activities not covered by the other three activities above.

Each time you run your program (by pressing the green triangle in Canopy) it should prompt the user to enter information about these activities and display a time profile. Below are three example executions of the time profiling program that show how your program should behave. In each run, text in black is displayed by the program, while text highlighed in magenta is entered by the user. (As in Task 1, in your actual program, the text entered by the user will also be displayed in black; we use magenta here only to clarify the distinction between text entered by the user and text displayed by the program.)

Sample Execution #1

What is your name? Valentina

How many classes are you taking this semester? 5

What is the average time in class per week this semester? 2.5

What shall we call the 'everything outside of class' category? fun

How many hours per week do you spend on 'fun'? 15

How many hours per day do you sleep on average? 8

Weekly time profile for Valentina:
37.5 class hours: CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
  15.0 fun hours: XXXXXXXXXXXXXXX
56.0 sleep hours: SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS
 59.5 free hours: FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

Sample Execution #2

What is your name? Emma

How many classes are you taking this semester? 4

What is the average time in class per week this semester? 3.67

What shall we call the 'everything outside of class' category? extracurricular

How many hours per week do you spend on 'extracurricular'? 22.5

How many hours per day do you sleep on average? 6.75

Weekly time profile for Emma:
         44.04 class hours: CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
22.5 extracurricular hours: XXXXXXXXXXXXXXXXXXXXXXX
         47.25 sleep hours: SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS
          54.21 free hours: FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

Sample Execution #3

What is your name? Sofia

How many classes are you taking this semester? 4

What is the average time in class per week this semester? 3.2

What shall we call the 'everything outside of class' category? chill

How many hours per week do you spend on 'chill'? 24

How many hours per day do you sleep on average? 6.55

Weekly time profile for Sofia:
 38.4 class hours: CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
 24.0 chill hours: XXXXXXXXXXXXXXXXXXXXXXXX
45.85 sleep hours: SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS
 59.75 free hours: FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

Note that each row of the profile has a number of characters that is the rounded version of the number of hours displayed on the row. So in Sofia's profile, there are 38 Cs, 24 Xs, 46 Ss and 60 Fs. . You should use Xs to indicate the number of 'everything outside of class' hours. Also note that each number of hours has at least one digit after a decimal point, and at most two.

Note also that your program should ask the user for the name of the category used to describe the 'everything outside of class' category, and then use that name in the remainder of the program. In the first example above, Valentina chose to use the name 'fun', Emma chose to use the label 'extracurricular', and Sofia chose to use the name 'chill'. The user of the program gets to decide which name to use to describe that category, and your program incorporates that name into the profile.

Finally, note that the rows the profile are aligned at the colons that separate the title of each row from the repeated characters. The colons should be aligned correctly regardless of what name is chosen for the 'activities outside of class' category.

In your account on the cs server is the CS111 download folder cs111/download. This folder contains a subfolder name ps01. Begin by copying this ps01 folder to your computer.

In this task, you will write a time profiling Python program timeProfiler.py from scratch in Canopy that has the behavior indicated by the sample executions above. You should save this file to the ps01 folder.

Your goal is to create a timeProfiler.py program that behaves exactly as indicated by the sample executions above, and works reasonably on other sample inputs.

Incremental Development

Any major programming task like this should be broken down into smaller subtasks.

For example, start by writing code to solve the subtask of prompting the user for their name and displaying the header "Weekly time profile for (name):"

Sample Execution for Subtask 1

What is your name? Sofia

Weekly time profile for Sofia:

Second, add a prompt for the number of sleep hours and add a corresponding line to the output display.

Sample Execution for Subtask 2

What is your name? Sofia

How many hours per day do you sleep on average? 6.55

Weekly time profile for Sofia:
45.85 sleep hours

Third, add a prompt for the name of the 'outside of class activities' category.

Sample Execution for Subtask 3

What is your name? Sofia

What shall we call the 'everything outside of class' category? chill

How many hours per day do you sleep on average? 6.55

Weekly time profile for Sofia:
45.85 sleep hours

Fourth, add a prompt for the number of -- in this particular case, chill -- hours, and add a corresponding line to the output display.

Sample Execution for Subtask 3

What is your name? Sofia

What shall we call the 'everything outside of class' category? chill

How many hours per week do you spend on 'chill'? 24

How many hours per day do you sleep on average? 6.55

Weekly time profile for Sofia:
24.0 chill hours
45.85 sleep hours

Continue in this way until you have prompts for all inputs and are able to produce the following (of course, your output will vary depending on what the user enters for the 'outside of class' category). Your program should be able to reproduce the sample executions above for Valentina, Emma and Sofia.

Sample Execution for Subtask 5

What is your name? Sofia

How many classes are you taking this semester? 4

What is the average time in class per week this semester? 3.2

What shall we call the 'everything outside of class' category? chill

How many hours per week do you spend on 'chill'? 24

How many hours per day do you sleep on average? 6.55

Weekly time profile for Sofia:
38.4 class hours
24.0 chill hours
45.85 sleep hours
59.75 free hours

Your remaining subtasks can now add in the repeated characters to create the plot and align everything correctly.

Note that this breakdown into subtasks is just one suggestion. You can break them down any way you prefer. However, trying to write the code for the entire program without breaking it down is a bad idea.

Notes

Later in the semester, we will learn how to check that the inputs are sensible and then require the user to enter valid inputs.

Running Codder on Task 2

To test that your timeProfiler.py program works as expected, you can use the Codder code feedback tool you saw in Lab 01, Part 3 to test your program.

Codder is now available for testing your timeProfiler.py program. Follow these steps:
  1. Go to https://cs.wellesley.edu/codder
  2. Authenticate yourself with your Wellesley domain name and password (do not use your cs.wellesley.edu password!)
  3. From the drop-down menu, select ps01 as the activity.
  4. Click on the Choose file button, and use the pop-up file selection window to navigate to your timeProfiler.py file.
  5. Click on the submit file button.

The Codder server will take a few seconds to respond with feedback on your code.

In the resulting report, pay attention to the parts marked in light purple, which highlight potential problems with your program. You should try to fix the reported issues in your program, and resubmit. You can resubmit your code as many times as you want.


Task 3: Graphics Scene

This task is a partner problem in which you are required to work with a partner as part of a two-person team.

The ps01 folder contains a copy of the cs1graphics package. We have also included a copy of the cs1graphicsHelper and graphicsState package (used in labs and lectures). In this task, you are to create a new file, scene.py, from scratch in the ps01 folder that creates your own novel scene on a Canvas object. Since we have a limited number of shapes at our disposal, we encourage abstract and creative artwork. Your scene.py file must satisfy the following criteria:

  1. Your file must start with comments at the top, identifying the authors, usernames, problem set number, filename, and date. Follow this format:

    # Wendy Wellesley and Abby Stracksen
    # wwellesl, astracks
    # CS111 Problem Set 1
    # scene.py
    # 09/12/2017
  2. Your file must appropriately import the cs1graphics package (and the cs1graphicsHelper package, if you opt to use it).
  3. Your canvas must have a descriptive title.
  4. You must use at least one instance of each of the following classes: Circle, Ellipse, Rectangle, Polygon, Path, and Text.

  5. You must vary the border thickness and colors of some shapes.
  6. You must vary the interior colors for some of your fillable objects, including at least one that has transparent color.
  7. You must include an Image in your scene. Note that this requires that you include the image file in your ps01 folder when you submit your assignment (GIF files tend to work best). It is OK if your image has a background that is not transparent. Your image will appear in its original form in your graphics scene. Although cs1graphics includes flipping, scaling and rotating, these operations do NOT work with imported images. If you try to flip/scale/rotate your image in cs1graphics, it will turn completely black. To avoid this, you may use Photoshop (or similar image-editing software) to manipulate your image to the desired size/orientation, and then import it into your scene.
  8. You must position at least one object so that it is partially obscuring another object in your scene.

You are welcome to use other cs1graphics features in addition to the ones listed above, but only the above features are required.

After completing this task, you must take a screenshot of your graphics scene, name it correctly, and upload it to the shared google drive folder here. See details below.

There is no Codder test for Task 3

Because Task 3 is an open-ended graphics problem, we do not supply a student-runnable version of Codder for this task.


Task 4: Honor Code Form

The ps01 folder contains a file honorcode.py with several variable assignments for your name, the time you spent on the tasks, etc. Change the values in these variable assignments to appropriate values.


How to turn in this Problem Set

In Task 3 you will take a screenshot of the output, which you will submit in addition to your code. Here are screenshot instructions.

Softcopy (electronic) submission (3 separate steps)

  1. Submit your code (every student)

    • Save your final debugNumsFixed.py and timeProfiler.py files in the ps01 folder.
    • Each team member should save their scene.py file in their ps01 folder. This file should contain a comment with names of both partners at the top.
    • Also, any image file (GIF files tend to work best) that you use in your graphics scene must be included in the ps01 folder.
    • Fill out the honorcode.py file and save it in the ps01 folder as well.

    • Note: It is critical that the name of the folder you submit is ps01, and it includes files named timeProfiler.py, scene.py, and honorcode.py. In other words, don't rename the folder that you downloaded, do not delete or rename any files in the 'ps01' folder, and use the exactly the names we have specified for any new files. (Running Canopy will automatically create some new files in your ps01 folder; you should not touch or delete these automatically generated files.)
    • Drop your entire ps01 folder in your drop folder on the cs server using Cyberduck by 11:59pm on Tuesday, Sep 11, 2018.
    • Failure to submit a code file before the deadline will result in zero credit for that code on PS01.
  2. Submit your screenshot (one per pair of students)

    Each pair of students in the course must upload a screenshot of their graphics scene to the the shared google drive folder.

    • Take a screenshot of your graphics scene (screenshot instructions here).
    • RENAME your screenshot with a short, unique descriptive name that begins with your CS account names. For example, wwellesl_astracks_underwaterMonkey.jpg.
    • Drag your properly named screenshot into the shared google drive folder by 11:59pm on Tuesday, Sep 11, 2018.

Hardcopy (paper) submission

There is no hardcopy submission. Pset submission is entirely electronic.