Introduction to Computer Science using Python


Class Info

Section 2: MWF 11:30–12:20, Sci Cntr 256 (the Birds' nest)
Professor: Jeff Knerr
Piazza: cs 21 Q&A forum
Office: Sci 238A (at back of 240 and 238)
Office hours: You can stop by whenever my door is open (usually not here Thursdays...)

Other Sections: Andrew Danner (MWF 9:30am–10:20pm) | Jason Waterman (TR 9:55am–11:10pm)

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.

Required Textbook:

Introduction to Computation and Programming Using Python by John V. Guttag
ISBN: 978-0262525008
We are using the revised and expanded edition
(a copy will be on reserve at Cornell Library)
guttag book

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.
1Sep 02   Introduction to Python and Unix
For loops
Sections 2.1, 3.2. Skip 2.1.3
In class: M W F
Lab 0: UNIX & vim
Sep 04  
Sep 06  
2Sep 09   Numbers and Strings
Sections 2.3, 3.4
In class: M W F
Lab 1: first programs
Sep 11  
Sep 13 Drop/add ends
3Sep 16 Quiz 1 Study Guide if/else; Booleans
Sec. 2.2
In class: M W F
Lab 2: numbers and strings
Sep 18 Quiz 1
Sep 20  
4Sep 23   While loops
Sec. 2.4
In class: M W F
Lab 3: if/elif/else
Sep 25  
Sep 27  
5Sep 30 Q2 Study Guide
Final Exam
Schedule Posted
(Oct 01)
Graphics, using objects
notes on the Zelle Graphics Library
In class: M W F
Lab 4: while loops
Oct 02 Quiz 2
Oct 04  
6Oct 07   Functions, objects
Sec. 4.1, 4.2
drawing stack frame example
In class: M W F
Lab 5: graphics
Oct 09  
Oct 11  

Oct 14

Fall Break

Oct 16

Oct 18

7Oct 21   Top Down Design, File I/O
Sec. 4.6, Chapter 6
In class: M W F
Lab 6: frog racing
Oct 23 Quiz 3 Study Guide
Oct 25 Quiz 3
8Oct 28   More Top Down Design
In class: M W F
Lab 7: hangman
Oct 30  
Nov 01  
9Nov 04 Quiz 4 Study Guide Searching, Analysis of Algorithms
Sec. 9.1, 9.3.1-9.3.3, 10.1
In class: M W F
Lab 7: still hangman
Nov 06 Quiz 4
Nov 08 CR/NC/W Deadline
10Nov 11   Sorting, Analysis of Algorithms
Sec. 10.2
In class: M W F
Lab 8: search stocks
Nov 13  
Nov 15  
11Nov 18 Quiz 5 Study Guide Recursion
Sec. 4.3
In class: M W F
Lab 9: campaign contributions
Nov 20 Quiz 5
Nov 22  
12Nov 25   Defining new classes and Linked Lists
Chapt. 8
In class: M W F
Lab 10: recursion
Nov 27  

Nov 29


13Dec 02   Linked lists In class: M W F
Lab 11: Population class
Dec 04 Quiz 6 Study Guide
Dec 06 Quiz 6
14Dec 09 Final Study Guide Wrap up In class: M
Lab 12: linked lists

Dec 13

Final Exams Start


Dec 19

Our CS21 Final: Thu, Dec 19, 7-10pm, Sci 101

Student Support

CS21 Ninjas are student mentors who will assist me in class and run evening study sessions in the birds' nest (Sci 256). The CS21 Ninjas (student mentors) are: Josh Gluck, Alexis Leanza, Sophie Libkind, Mallory Pitser, Karl Sadueste, and Ravenna Thielstrom.

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 food will be provided at the sessions. The sessions are held:

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

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. Additionally, the cs labs are open 24 hours a day, 7 days a week for you to use for CS21 lab assignments. While you must attend the lab session for which you are registered, you may optionally attend additional lab sessions, provided space is available. In case of space constraints, students registered for the lab will have seating priority.

Weekly Lab Sessions
1:05—2:35pm Tuesdays Danner Science Center 256
2:45—4:15pm Tuesdays Knerr Science Center 256
1:05—2:35pm Thursdays Waterman Science Center 256
2:45—4:15pm Thursdays Wicentowski Science 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 on the door handle 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 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.

How to Succeed in CS 21

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.


Grades will be weighted as follows:
40%Lab assignments
25%Final Exam
5%Class Participation

Quiz policy

Quizzes will be given at the beginning of class on the days posted in the Announcements section of 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 at the start of class on the day of a quiz, but make it to class before the end, then you may take the quiz. Otherwise you will receive a zero for that quiz.

Lab policy

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 assignments will only be accepted if you contact the professor at least a day before the deadline with a legitimate reason for needing extra time, such as an illness or needing to leave campus.

Even if you do not fully complete an assignment, you should submit what you have done to receive partial credit.

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:

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

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, code found in the course text book, and code worked on with an assigned partner. 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."

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

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

Vi Quick Reference
Python style guide From Prof. Tia Newhall
Using Unix
Basic Unix Commands
Python Documentation (Note: we are using v2.7)
Graphics reference
How To Think Like a Computer Scientist: Python for Software Design
Dive Into Python
(A Semi-Official) Python FAQ Zone