CS 21: Intro to Computer Science - Fall 2025

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.

Meeting Times:

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:

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

This semester, we will be using Standards Based Grading.

This course features weekly lab assignments which are a significant component of your course grade and overall learning. Lab attendance is required by all students. You must attend the lab session for which you are enrolled.

Lab assignments will typically be released on Monday at the beginning of the week and will be due by midnight on Sunday unless otherwise noted on the syllabus. You are strongly encouraged to start early and to attend the ninja sessions for extra practice.

You will submit your 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.

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. Discussing ideas and approaches to problems with others on a general level is encouraged, but you should never share your solutions with anyone else nor allow others to share solutions with you. You may not examine solutions belonging to someone else, nor may you let anyone else look at or make a copy of your solutions. This includes, but is not limited to, obtaining solutions from students who previously took the course or solutions that can be found online. The use of generative AI (e.g., chatGPT or GitHub CoPilot) is also considered to be unauthorized collaboration with an outside source and is a violation of our academic integrity policy.

You may not share information about your solution in such a manner that a student could reconstruct your solution in a meaningful way (such as by dictation, providing a detailed outline, or discussing specific aspects of the solution). You may not share your solutions even after the due date of the assignment.

In your solutions, you are permitted to include material which was distributed in class, material which is found in the course textbook, and material developed by or with an assigned partner. In these cases, you should always include detailed comments indicating on which parts of the assignment you received help and what your sources were.

When working on quizzes, exams, or similar assessments, you are not permitted to communicate with anyone about the exam during the entire examination period (even if you have already submitted your work). You are not permitted to use any resources to complete the exam other than those explicitly permitted by course policy. (For instance, you may not look at the course website during the exam unless explicitly permitted by the instructor when the exam is distributed.)

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:

This policy applies to all course work, including but not limited to code, written solutions (e.g. proofs, analyses, reports, etc.), exams, and so on. This is not meant to be an enumeration of all possible violations; students are responsible for seeking clarification if there is any doubt about the level of permissible communication.

The general ethos of this policy is that actions which shortcut the learning process are forbidden while actions which promote learning are encouraged. Studying lecture materials together, for example, provides an additional avenue for learning and is encouraged. Using a classmate’s solution, however, is prohibited because it avoids the learning process entirely. If you have any questions about what is or is not permissible, please contact your instructor.

If you commit some act that is a violation of the integrity policy (or, if you are unsure if it violates the policy) but bring it to the attention of the course’s instructors within 48 hours, the course may impose local sanctions that may include an unsatisfactory or failing grade for work submitted, but the course will not refer the matter for further disciplinary action except in cases of repeated acts. The regret clause applies to lab assignments only.

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.

The CS21 Ninjas (student mentors) are: Rania Abohatab, Elizabeth Bugayev, Alex Coley, Michelle (Ziyuan) Fang, Lona Hoang, Gia (Yaejie) Kwon, Erin Picken, Emma Shi, Phelps (Yuxan) Wang.

If you believe you need accommodations for a disability or a chronic medical condition, please contact Student Disability Services (via email at studentdisabilityservices@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 official accommodation letter from the Office of Student Disability Services and you need to meet with course staff to work out the details of your accommodation at least two weeks prior to the activity.

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

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:

CS labs are accessible for you to use 24 hours a day, 7 days a week. You can access CS labs using your OneCard.

For CS21, the easiest way to connect to the CS machines from your own laptop is to install Visual Studio Code and set it up to remotely access your files. To do this, follow the instructions on how to setup Visual Studio Code for remotely accessing the CS department.

You can also remotely access the CS lab machines using ssh. However, you cannot easily run the code editor remotely connecting in this way. Directly ssh’ing into CS lab machines is useful if you want to run shell commands, or if you use a different editor like vim or emacs.

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