CS21:Intro to Computer Science

(Fall 2018)

Course Info | Schedule | Grading | Academic Integrity
Student Support | Tips for Success | Code Style | Piazza | Links


  • Lab 11 is due SUNDAY December 9
  • Our final exam is Saturday December 15 at 2pm in Sci Center 101

Course Information

Section 2: MWF 10:30–11:20, Sci 256
Professor: Sara Mathieson
Office: Sci 249
Office hours: Fridays, 3-5pm
Lab Instructor: Sara "Scout" Sinclair
Office: Sci 262A
Office hours: Mondays, 2-3:30 and Thursdays, 10:30-11:30

Piazza: CS21 Q&A forum

Links to all sections:

Welcome to CS21. This course will introduce fundamental ideas in computer science while also teaching you how to write computer programs. We will study algorithms for solving problems and implement solutions in the Python programming language. Python is an interpreted language that is known for its ease of use. We also introduce object-oriented programming and data structures. A deeper coverage of these topics will be presented in CS 35.

This course is appropriate for all students who want to learn how to write computer programs and think like computer scientists. It is the usual first course for computer science majors and minors. Students with advanced placement credit or extensive programming experience should place out of this course and instead begin with CS31 or CS35.


book pic We will primarily be using the online book How to think like a computer scientist: Learning with Python by Elkner, Downey and Meyers.

See the Schedule for each week's reading assignment.

Here are a few other useful online resources:

Goals for the course:

By the end of the course, we hope that you will have developed the following skills:


Here is the tentative schedule; it may change as we go...

Sep 03


Course Introduction




Lab 0: Unix, Editing
Lab Notes

Sep 05


Sep 07


Sep 10


Numbers, Strings, and Loops




Lab 1: First Programs

Sep 12


Sep 14

Drop/add ends


Sep 17


Conditions and Boolean Logic




Lab 2: Numbers and Strings
Lab Notes

Sep 19

Q1 study guide

Sep 21

Quiz 1


Sep 24


First Functions, while Loops




Lab 3: If/Else

Sep 26


Sep 28


Oct 01


Fruitful Functions




Lab 4: While loops/Functions

Oct 03

Q2 study guide

Oct 05

Quiz 2


Oct 08


Graphics, Using Objects




Lab 5: More Functions
Lab Notes

Oct 10


Oct 12


Oct 15

Fall Break

Oct 17

Oct 19


Oct 22


Top-Down Design




Lab 6: Graphics

Oct 24


Oct 26


Oct 29








Lab 7: Top-Down Design

Oct 31

Q3 study guide

Nov 02

Quiz 3


Nov 05



Nov 07


Nov 09

CR/NC/W Deadline


Nov 12






Lab 8: Searching

Nov 14

Q4 study guide

Nov 16

Quiz 4


Nov 19


Classes and Objects



Lab 9: Sorting

Nov 21


Nov 23



Nov 26


Classes and Objects




Lab 10: Classes

Nov 28

Q5 study guide

Nov 30

Quiz 5


Dec 03






Lab 11: Recursion

Dec 05


Dec 07


Dec 10

Final study guide

Wrap up


Dec 15

Final Exam: Sat, Dec 15, 2-5pm, Sci Cen 101

Grading Policies

Grades will be weighted as follows:
35%Lab assignments
30%Final Exam
5%Class Participation

Exam and Quizzes

Quizzes will be given at the beginning of class on the days posted on the Schedule. Please look over these dates carefully and contact the professor in advance if you cannot be in class for a quiz.

If you are not present on the day of a quiz, and do not let me know ahead of time that you are missing class, you will receive a zero for that quiz.

There will be one final exam for the semester. Details and dates will be released during the semester. Please read the section on accommodations if you are in need of extra time. You must inform me of accommodations or conflicts at least 2 weeks in advance of the exam.

Lab Policy

This course features weekly lab assignments which are the largest component of your course grade. Lab attendance is required by all students, unless you have already completed and submitted the lab assignment for the week. You must attend the lab session for which you are enrolled:

Weekly Lab Sessions
CS21 A 1:15—2:45pm Tuesdays Sara Mathieson Sci 240
CS21 B 3:00—4:30pm Tuesdays Scout Sinclair Sci 240
CS21 C 1:15—2:45pm Wednesdays Aline Normoyle Sci 240
CS21 D 3:00—4:30pm Wednesdays Aline Normoyle Sci 240

Lab assignments will typically be assigned in class at the beginning of the week and will be due before midnight on Saturdays. You are strongly encouraged to start early and to attend the study sessions for extra practice.

You will submit you assignments electronically using the handin21 program. You may submit your assignment multiple times, and a history of previous submission will be saved. You are encouraged to submit your work regularly.

Late Policy:

Each individual will be given 2 late days for the semester, as per the CS department policy. A late day is a 24 hour extension from the original deadline. You can use one day on two assignments or both days on one assignment. This will encompass any reason - illness, interviews, many midterms in the same week, etc. Past these days, late assignments will not be accepted. You should budget your days to account for future illnesses or assignment deadlines for other courses. Even if you do not fully complete a lab assignment you should submit what you have done to receive partial credit.

The CS labs are open 24 hours a day, 7 days a week for you to use for CS21 lab assignments.

If you feel that you need an extension on an assignment (beyond your late days) or that you are unable to attend class for two or more meetings due to a medical condition (e.g., extended illness, concussion, hospitalization) or other emergency, you must contact the dean's office and your instructors. Faculty will coordinate with the deans to determine and provide the appropriate accommodations. Note that for illnesses, the College's medical excuse policy, states that you must be seen and diagnosed by the Worth Health Center if you would like them to contact your class dean with corroborating medical information.

Academic Integrity

Academic honesty is required in all your work. Under no circumstances may you hand in work done with (or by) someone else under your own name. Your code should never be shared with anyone; you may not examine or use code belonging to someone else, nor may you let anyone else look at or make a copy of your code. This includes, but is not limited to, obtaining solutions from students who previously took the course or code that can be found online. You may not share solutions after the due date of the assignment.

Discussing ideas and approaches to problems with others on a general level is fine (in fact, we encourage you to discuss general strategies with each other), but you should never read anyone else's code or let anyone else read your code. All code you submit must be your own with the following permissible exceptions: code distributed in class, and code found in the course text book. In these cases, you should always include detailed comments that indicates on which parts of the assignment you received help, and what your sources were.

Failure to abide by these rules constitutes academic dishonesty and will lead to a hearing of the College Judiciary Committee. According to the Faculty Handbook: "Because plagiarism is considered to be so serious a transgression, it is the opinion of the faculty that for the first offense, failure in the course and, as appropriate, suspension for a semester or deprivation of the degree in that year is suitable; for a second offense, the penalty should normally be expulsion." Be aware that we will be routinely running plagiarism detection software on the lab solutions of students from all sections of CS21.

The spirit of this policy applies to all course work, including code, homework solutions (e.g., proofs, analysis, written reports), and exams. Please contact me if you have any questions about what is permissible in this course.

Exam Integrity

Students must strictly adhere to the following policy, which applies to all exams taken in a Computer Science course at Swarthmore:

Exam takers must place all non-essential items at the front of the room (or other designated area). Unless otherwise permitted, students may not have any electronic devices or course materials in their possession during the entirety of the exam. This includes cell phones, tablets, laptops, smart watches, course notes, articles and books, among others. These items should be placed at the front of the room near the proctor. If you need to leave the room during the exam, you must obtain permission from an instructor first. Any non-permitted discussion or aide in regards to exam material will result in immediate forfeiture of the exam and a report to the College Judiciary Committee. Please discuss any concerns or accommodations with your instructor prior to starting the exam.

Student Support

Lauri Courtenay is the CS Department's Academic Support Coordinator. She will be working closely with our student mentors, also known as Ninjas, to help you learn how to program and think like a computer scientist. The CS21 Ninjas will assist me in class and run evening study sessions in the birds' nest (Sci 256). The CS21 Ninjas (student mentors) are: Ariel (Sky) Overdorff, Kenny Mai, Christie Little, Kendre Thomas, Rohan Hejmadi, Ayaka Yorihiro, Maleya Peterson, Shayne Rothman, Zachary Viscusi, Michael Kourakos, Tai Thonghai, and Tristan Cates.

Study Sessions

You are invited -- and encouraged -- to participate in Ninja evening study sessions to prepare for quizzes, to discuss programming concepts, and to get friendly assistance in working on lab assignments. Our CS mentoring team is dedicated to helping students, who have no prior knowledge of computer science, learn to program in Python while keeping their senses of humor intact. As an added bonus, free snacks will be provided at the sessions. The sessions are held:

Weekly Evening Ninja Sessions
Wednesdays 7—10pm Sci Center 256
Fridays 7—9pm Sci Center 256

Accessing the CS labs after hours

You can use your ID to gain access to the computer labs at nights and on the weekends. Just wave your ID over the microprox reader next to the lab doors. When the green light goes on, just push the door to get in (the door knob will not turn). If the green light doesn't go on, then we need to enter your microprox number into the system. Email local-staff@cs.swarthmore.edu (or see Bridget) if you have problems with this. If the building is locked, you can use your ID to enter the door between Martin and Cornell library. For this class, your ID will give you access to the labs in rooms 238, 240, and 256 and Clothier 16.

Academic Accommodations

If you believe you need accommodations for a disability or a chronic medical condition, please contact Student Disability Services (Parrish 113W, 123W) via e-mail at studentdisabilityservices at swarthmore.edu to arrange an appointment to discuss your needs. As appropriate, the office will issue students with documented disabilities or medical conditions a formal Accommodations Letter. Since accommodations require early planning and are not retroactive, please contact Student Disability Services as soon as possible. For details about the accommodations process, visit the Student Disability Services website.

To receive an accommodation for a course activity, you must have an Accommodation Letter from the Office of Student Disability Services and you need to meet with me to work out the details of your accommodation at least two weeks prior to the activity.

You are also welcome to contact me privately to discuss your academic needs. However, all disability-related accommodations must be arranged, in advance, through Student Disability Services.

How to Succeed in CS 21

Programming Style

Programming is not a dry mechanical process, but a form of art. Well written code has an aesthetic appeal while poor form can make other programmers and instructors cringe. Programming assignments will be graded based on style and correctness. Good programming practices usually include many of the following principles:


This semester we’ll be using Piazza, an online Q&A forum for class discussion, help with labs, clarifications, and announcements that pertain to all sections of cs21. You should have received an email invitation to join CS21 on Piazza. If you didn't, please let us know.

Piazza is meant for questions outside of regular meeting times such as office hours, ninja sessions, class, and lab. Please do not hesitate to ask and answer questions on Piazza, but keep in mind the following guidelines:

  1. Piazza should be used for ALL content and logistics questions outside of class, lab, office hours, and ninja sessions. Please do not email instructors or ninjas with your code or questions about the assignments.
  2. If there is a personal issue that relates only to you, please email your instructor.
  3. We encourage non-anonymous posts (which will count towards participation), but you may post anonymously.
  4. Do NOT post long blocks of code on Piazza - if you can distill the problem to 1-2 lines of code and an error message, that’s fine, but try to avoid giving out key components of your work.
  5. By the same token, when answering a question, try to give some guiding help but do not post code fixes or explicit solutions to the problem.
  6. Posting on Piazza counts toward your participation grade, both asking and answering!

Links that are related to the course may be posted here. If you have suggestions for links, let me know.

Using Unix
Basic Unix Commands
Remote access with atom