CS21:Intro to Computer Science

(Spring 2019)

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


  • There will be a Final Exam review session on May 8 from 10AM-12PM in SCI 181. Here is a study guide.
  • A small Optional lab12 is available for some practice working with dictionaries. This lab will not be graded.

Course Information

Jump to this week
Section 2: MWF 10:30–11:20, Sci 256
Professor: Joshua Brody
Office: Science Center 260
Office hours: Thursdays 2-4pm
Lab Instructor: Sara "Scout" Sinclair
Office: Sci 262A
Office hours: Thursdays 11:15-12:15, Fridays 3-4pm

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...

Jan 23


Course Introduction

Wed notes


Fri notes


Lab 0: UNIX, editing

Jan 25


Jan 28


Numbers, Strings, and Loops

Mon notes

Wed notes


Fri notes

Lab 1: First Programs

Jan 30


Feb 01

Drop/add ends


Feb 04

Quiz 1 Study Guide

Conditions and Boolean Logic


Lab 2: Numbers and Strings

Feb 06


Feb 08

Quiz 1


Feb 11


First Functions, while Loops

Week 4 Notes

Lab 3: if statements, for loops

Feb 13


Feb 15


Feb 18

Quiz 2 Study Guide

Fruitful Functions

Week 5 Notes

Lab 4: while loops, functions

Feb 20


Feb 22

Quiz 2


Feb 25


Graphics, Using Objects

Week 6 Notes

Lab 5: more functions

Feb 27


Mar 01


Mar 04

Quiz 3 Study Guide

Top-Down Design

Week 7 Notes

Lab 6: Graphics, Objects

Mar 06


Mar 08

Quiz 3


Mar 11

Spring Break

Mar 13

Mar 15


Mar 18


Top-Down Design


Week 8 Notes - TDD
Week 9 Notes - Search
Lab 7: Top Down Design

Mar 20


Mar 22


Mar 25



Mar 27

Quiz 4 Study Guide

Mar 29

CR/NC/W Deadline

Quiz 4


Apr 01



Week 10 Notes
Lab 8: Searching ZIP Codes

Apr 03


Apr 05


Apr 08

Quiz 5 Study Guide


Week 11 Notes
Lab 9: Sorting

Apr 10


Apr 12

Quiz 5


Apr 15


Classes and Objects

Week 12 Notes
Lab 10: Recursion

Apr 17


Apr 19


Apr 22

Quiz 6 Study Guide

Classes and Objects

Week 13 Notes
Lab 11: SpaceBlaster

Apr 24


Apr 26

Quiz 6


Apr 29


Dictionaries Course Wrap up

Week 14 Notes

May 01


May 03


May 12

Final Exam: Sun. 12 May, 9a-Noon, 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 us 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 us 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 Scout Sinclair Sci 256
CS21 B 3:00—4:30pm Tuesdays Scout Sinclair Sci 256
CS21 C 1:15—2:45pm Wednesdays Andrew Danner Sci 256
CS21 D 3:00—4:30pm Wednesdays Joshua Brody Sci 256

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:

Labs will typically be due Saturdays before midnight. Late submissions will not be accepted. 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 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 us 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 us in class and run evening study sessions in the birds' nest (Sci 256). The CS21 Ninjas (student mentors) are: Elvis Adorkor, Ali Baratta, Rohan Hejmadi, Misha Khan, Adriana Knight, Peem Lerdputtipongporn, Christie Little, Fefa Sampaio Ferreira, Bilal Soukouna, Kendre Thomas, Bayliss Wagner, Haochen Wang, and Tiffany Zheng

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 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 us to work out the details of your accommodation at least two weeks prior to the activity.

You are also welcome to contact us 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 us know.

Using Unix
Basic Unix Commands
Remote access with atom