Introduction to Computer Science using P Y T H O N -- FALL 2012


Class Info

Section 2: MWF 11:30–12:20, Sci Cntr 240
Professor: Jeff Knerr
email: knerr at
Office: Science Center 238A (door at the back of the lab)
Phone: X5758
Office hours: You can stop by whenever my door is open.

Other Sections: Andy Danner (MWF 9:30–10:20am) Jason Waterman (TT 9:55–11:10am)

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 CS35.

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 CS33 (or CS31) or CS35.

Required Textbook:

  • Python Programming: an Introduction to Computer Science, First Edition by John Zelle
    ISBN: 978-1-887902-99-1
    (a copy is on reserve at Cornell Library)
    zelle book

    Goals for the course:

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

    • Given a program, be able to simulate on paper how a computer would execute the program, and show the results that would be produced.
    • Given a problem, be able to design a clear, concise, and correct pseudo-code algorithm to solve it.
    • Given a pseudo-code algorithm, be able to successfully implement it in Python.
    • Be able to use top-down design to sub-divide a large problem into reasonably-sized modular sub-problems.
    • Given several algorithms for solving the same problem, be able to analyze which algorithm would be more efficient in terms of running time.
    • Develop debugging and unit testing skills. Consistently use these skills while implementing programs.
    • Learn to work as part of a team to solve problems starting from design and continuing through to implementation.

    Student Support

    Student Support Coordinator: Frances Ruiz (office: 257 Sci Ctr, phone: x6062)
    CS21 Ninjas (student mentors): Jake Weiner, Katherine Hamilton, Justin Cosentino, Molly Feldman, Jocelyn Adams, and Cynthia Ma.

    Justin and Molly will attend our class, but all will be able to help you with class concepts, quizzes and labs.

    Study sessions

    The CS Ninjas will assist me in class and run study sessions in the main CS lab (Science Center 240) on the following evenings:

    Day Time Location
    Sundays 7-10pm Sci Center 240
    Wednesdays 7-9pm Sci Center 240

    You are invited (and encouraged!!) to participate in these study sessions to prepare for quizzes, to discuss programming concepts, and to get friendly assistance in working on homework 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.

    Lab Sessions

    The CS lab is open 24 hours a day, 7 days a week for you to use for CS21 lab assignments. In addition, the CS21 professors will be in the CS labs at the times listed below to help CS21 students with lab assignments. You are not required to attend any of these sessions, but you should take advantage of them to get assistance with your lab assignments. Any CS21 student is welcome to attend any/all session.

    Time Professor Location
    1:30-3:00 Mondays Danner Science Center 240
    2:30-4:00 Mondays Waterman Science Center 240
    2:00-3:30 Fridays Knerr Science Center 240

    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 and 240.

    How to Succeed in CS 21

    • Attend class.
      The primary introduction to course material is through class lecture. Additionally, we often do lab exercises during class. This is an important part of the learning process, as these exercises give you immediate experience with the material we are covering.
    • Read the assigned pages in the textbook before you come to class.
      Don't worry about total comprehension, but at least get a feel for what we will be covering that week. If you have some understanding of the material coming into class, it will be easier for you to ask questions during class, rather than later when help may not be available.
    • Ask questions if you don't understand.
      This means both during class and while doing lab assignments . This class continually builds on previous material, so if you don't understand something one week, it will continue to be a problem the next week, and the week after that, and so on. If you need help, ask your classmates (make sure you have read the "Academic Integrity" section below first), attend the lab and study sessions, come talk with me during my office hours, or email me your question.
    • Start the lab assignments early.
      I realize this one is not always easy to do, but if you can get in the habit of doing this, you will be much better off. If you get stuck early (i.e., not two hours before it is due), there will be time to look for help. In addition, if you start early enough, you can take a break, go do something else, and come back later. I find I always have at least a few new ideas when I come back to a problem after a break. If you wait until the last minute, you can't do this.
    • Practice, practice, practice.
      The only effective way to learn the material and pass the quizes and exams is to consistently do the labs. Finish all of the assigned programs (and do some extras, for fun!). Even if you don't get them done on time, they will still help you learn the material.
    • Seek help early and often.
      Because course material builds on previous material, it is essential to your success in this class that you keep up with the course material. If you are having difficulty with a programming assignment, if you didn't follow something covered in lecture, if you feel you need some extra help understanding or practicing some of the course material, or if you just want to discuss something from a lecture, an assignment, or the text, please come to my office hours.
    • Attend CS21 Labs and Study Sessions.
      The student Ninjas hold evening study sessions each week. You are encouraged to participate in these sessions. The Ninjas will help you prepare for quizzes, will provide additional instruction in programming concepts, and will provide friendly assistance on your lab assignments. The CS 21 professors hold lab sessions each week. You are encouraged to attend these to get help with lab assignments.
    • Take hand written lecture notes.
      In lecture the professor often draws diagrams on the board, some of which you will need to reproduce. Taking notes with paper and pen (vs. on the computer) will allow you to copy these diagrams.

    Academic Accommodations

    If you believe that you need accommodations for a disability, please contact Leslie Hempling in the Office of Student Disability Services, located in Parrish 130, or e-mail lhempli1 to set up an appointment to discuss your needs and the process for requesting accommodations. Leslie Hempling is responsible for reviewing and approving disability-related accommodation requests and, as appropriate, she will issue students with documented disabilities an Accommodation Authorization Letter. Since accommodations may require early planning and are not retroactive, please contact her as soon as possible. For details about the Student Disabilities Service and the accommodations process, visit the Disability Services webpage.

    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 be posted on the Schedule in the middle of the week and will be due before midnight the following Tuesday night. 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, but each submission overwrites the previous one and only the final submission will be graded.

    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. Unless otherwise stated, labs are to be completed individually. Please carefully read the statement on academic integrity for more information.

    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:

    • A comment at the top of the program that includes
      • Program authors
      • Date or Dates
      • A brief description of what the program does
    • Concise comments that summarize major sections of your code
    • Meaningful variable and function names
    • Function comments that include:
      1. description of what function does
      2. description of input values (parameter values)
      3. description of return value(s)
    • Well organized code
    • White space or comments to improve legibility
    • Avoidance of large blocks of copy-pasted code
    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 work you submit to be graded. You may not submit work done with (or by) someone else, or examine or use work done by others to complete your own work. 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 sharing solutions after the due date of the assignment.

    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.

    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. You may discuss assignment specifications and requirements with others in the class to be sure you understand the problem. In addition, you are allowed to work with others to help learn the course material. However, with the exception of your lab partner, you may not work with others on your assignments in any capacity.

    "It is the opinion of the faculty as a whole that for an intentional first offense failure in the course normally is appropriate. Suspension for a semester or deprivation of the degree in that year may also be appropriate when warranted by the seriousness of the offense." - Swarthmore Student Handbook

    Please see me if there are any questions about what is permissible.


    This is a tentative schedule; it may change as we go.
    1Sep 03   Introduction to Python and Unix
    Chapt. 1-2
    In class: M W F
    Lab 0: UNIX & vim
    Lab 1: first programs
    Sep 05  
    Sep 07  
    2Sep 10   Loops, Numbers and Strings, Indexing
    Chapt. 3-4 (Skip 4.6)
    In class: M W F
    Lab 2: numbers and strings
    Sep 12 Quiz 1 Study Info
    Sep 14 Quiz 1; drop/add ends
    3Sep 17   Booleans, Branching
    Chapt. 7.1, 7.2, 7.3 and 8.4.1 p. 246-247
    In class: M W F
    Lab 3: pirate adventure
    Sep 19  
    Sep 21  
    4Sep 24   Graphics, using Objects
    Chapt. 5 (skip 5.5, 5.6)
    notes on the Graphics Library
    In class: M W F
    Lab 4: graphics
    Sep 26 Quiz 2 Study Info
    Sep 28 Quiz 2
    5Oct 01 Final Exam Schedule Functions, objects
    Chapt. 6 (skip 6.3)
    In class: M W F
    Lab 5: snails
    Oct 03  
    Oct 05  
    6Oct 08   Indefinite Loops, More Functions
    Chapt. 8.1, 8.2, 8.3
    In class: M W F
    Lab 6: typing tutor
    Oct 10 Quiz 3 Study Info
    Oct 12 Quiz 3

    Oct 15

    Fall Break

    Oct 17

    Oct 19

    7Oct 22   Top Down Design, File I/O
    Chapt. 9.1, 9.2, 9.3, 4.6
    In class: M W F
    Lab 7: lingo
    Oct 24  
    Oct 26  
    8Oct 29   More Top Down Design, File I/O
    Chapt. 9.1, 9.2, 9.3, 4.6
    In class: M W F
    Lab 7: lingo
    Oct 31 Quiz 4 Study Info
    Nov 02 Quiz 4
    9Nov 05   Searching, Analysis of Algorithms
    Chapt. 13.1
    In class: M W F
    Lab 8: searching
    Nov 07  
    Nov 09 CR/NC/W Deadline
    10Nov 12   Sorting, Analysis of Algorithms
    Chapt. 13.2, 13.3
    In class: M W F
    Lab 9: zipcodes
    Nov 14 Quiz 5 Study Info
    Nov 16 Quiz 5
    11Nov 19   Recursion
    Chapt. 13.1-13.3
    In class: M W
    Lab 10: bucket fill
    Nov 21  

    Nov 23


    12Nov 26   Defining new classes and Linked Lists
    Chapt. 10.1, 10.3, 10.4
    In class: M W F
    Lab 11: fire simulator
    Nov 28  
    Nov 30  
    13Dec 03   Linked lists
    In class: M W F
    Lab 12: linked lists
    Dec 05 Quiz 6 Study Info
    Dec 07 Quiz 6
    14Dec 10   Wrap up In class: M

    Dec 14

    Finals Exams Start

    Dec 15

    Our CS21 Final: Sat, Dec 15, 7-10pm, Sci 101

    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 Improved
    Basic Unix Commands
    Python Documentation (Note: we are using v2.7)
    How To Think Like a Computer Scientist: Python for Software Design
    Zelle Textbook site
    Dive Into Python
    (A Semi-Official) Python FAQ Zone
    NodeBox (for Mac OS X)