CS21:Intro to Computer Science

(Mauskop/Spring 2017)

Course Info | Schedule | Grading | Academic Integrity
Student Support | Tips for Success | Code Style | Links
Introduction to Computer Science using Python


  • The final exam is on Saturday, May 6 from 7-10pm in Science Center 101
  • Lab 12 is optional, but is a good way to practice linked lists for the final exam.
  • Classes practice and answers
  • Recursion practice and answers
  • Final exam review sessions:
    • Wednesday, May 3: 1-2:30pm, 181 Science Center (Mauskop)
    • Thursday, May 4: 2:30-4pm, 183 Science Center (Newhall)
    • Friday, May 5: 1-2:30pm, 181 Science Center (Knerr)
  • Slides from Wednesday's review session: here

Course Information

Section 1: MWF 9:30–10:20, Science Center 256
Professor: David Mauskop
Office: Science Center 262A
Office hours: Thursday, 2-4pm

Other Sections:

Welcome to CS21. This course will introduce you to fundamental ideas in computer science while teaching you how to write computer programs. We will study algorithms for solving problems and implement solutions in the Python programming language. Python is known for its ease of use and wide-ranging applicability. We also introduce object-oriented programming and data structures. A deeper coverage of these topics is 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. We assume no prior experience with programming. 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:


This is a tentative schedule; it may change as we go.

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 1:05—2:35pm Tuesdays Knerr Science Center 240
CS21 B 2:45—4:15pm Tuesdays Newhall Science Center 240
CS21 C 1:15—2:45pm Wednesdays Mauskop Science Center 240
CS21 D 3:00—4:30pm Wednesdays Mauskop Science Center 240

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

Late Policy:

Late assignments are not accepted and will receive zero credit (see exceptions below). Even if you do not fully complete an 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.

Please contact me if you have any questions about what is permissible in this course.

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 Sci 256. The CS21 Ninjas (student mentors) are: Annie Zhao, Colin Pillsbury, Carlo Sivilotti, Jeffrey Novak, Nhung Hoang, Rye Buckley, Kyra Moed, Kei Imada, Zoe Kyaw, and Katherine Huang.

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. The sessions are held:

Weekly Evening Ninja Sessions
Tuesday 7—9pm Sci Center 256
Wednesday 7—10pm Sci Center 256
Friday 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 weekends. Wave your ID over the microprox reader to gain entry. 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 that you need accommodations for a disability, please contact Leslie Hempling in the Office of Student Disability Services (Parrish 113) or email lhempli1 to arrange an appointment to discuss your needs. As appropriate, she will issue students with documented disabilities a formal Accommodations Letter. Since accommodations require early planning and are not retroactive, please contact her as soon as possible. For details about the accommodations process, visit the Student Disability Service website.

To receive an accommodation for a course activity, you must have an Accommodation Authorization letter from Leslie Hempling and you need to meet with me to work out the details of your accommodation at least one week 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 through Leslie Hempling in the Office Of Student Disability Services.

How to Succeed in CS 21

Programming Style

Programming assignments will be graded based on style and correctness. A well-styled program includes the following:

Also, look over the Python Code Style Guide for more details and some examples of good code style.

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

Algorithms to Live By...
Think Python
Python Tutor
Vi Quick Reference
Python style guide From Prof. Tia Newhall
Using Unix
Basic Unix Commands
Python Documentation (Note: we are using v2.7)