Due at 11:59pm on 09/03/2015.

Starter Files

Download lab00.zip. Inside the archive, you will find starter files for the questions in this lab, along with a copy of the OK autograder.


By the end of this lab, you should have submitted the lab with python3 ok --submit. You may submit more than once before the deadline; only the final submission will be graded.


This lab explains how to use your own computer to complete assignments for CS 61A. If you are using a school computer, most of the instructions are the same, except you won't have to install anything.

Setting up

Installing a terminal

The terminal is a program that allows you to interact with your computer by entering commands. No matter what operating system you use (Windows, MacOS, Linux), the terminal will be an essential tool for CS 61A.

If you're on a Mac or are using a form of Linux (such as Ubuntu), you already have a program called Terminal on your computer. Open that up and you should be good to go.

For Windows users, we recommend downloading a terminal called GitBash.

Installing Python 3

Python 3 is our primary programming language. You can get Python here. Download one of the installers (for example, "Windows x86-64 MSI installer" or "Mac OS X 64-bit installer"). If your computer is a 64-bit machine, you should download the 64-bit installer. (In general, if your computer is new within the past 2 years, it is likely 64-bit. Ask a TA or lab assistant if you're not sure.)

MacOS users can refer to this video for additional help on setting up Python.

If you're having trouble opening the installer, you can right-click the icon and select "Open".

For Windows users, if you're installing a more recent version of Python, you should make sure to specify during setup to 'Add python.exe to Path', which will allow you to execute the python command from your terminal.

Windows PATH at setup

You can also refer to this video for additional help on setting up Python (up to 1:09 into the video).

If you did not see the aforementioned option during setup, then you will need to manually configure your PATH environment variable; the same video describes how to do this from 5:00 to 5:54.

Installing a text editor

The Python interpreter that you installed earlier allows you to run Python code. You will also need a text editor, which will help you write Python code.

A text editor is a program that allows you to edit text files, and often comes with tools to help you customize your experience. You will be using a text editor to create, modify, and save files.

There are many editors out there, each with its own set of features. We find that Sublime Text 2 and Atom are popular choices among students, but you are free to use other text editors.

Note: Please, please, please do not use Microsoft Word to edit programs. Word is designed to edit natural languages like English — trouble will ensue if you try to write Python with Word!

For your reference, we've also written some guides on using popular text editors. After you're done with lab, you can take a look if you're interested:

Open a terminal

First, open a terminal, if you haven't already.

starting the terminal

Right now, I'm in my home directory. The home directory is represented by the ~ symbol. When you first open your terminal, you will start in the home directory.

Don't worry if your terminal window doesn't look exactly the same; the important part is that the text on the left hand side is relatively the same (with a different name) and you should definitely see a ~ (tilde).

Organize your files

In this section, we will be learning terminal commands to manage our files.


The first command we'll use is ls. Try typing it in the terminal:


The ls command lists all the files and folders in the current directory. A directory is another name for a folder (such as the Documents folder). Since we're in the home directory right now, you should see the contents of your home directory.

Making new directories

Our next command is called mkdir, which makes new directories. Let's make a directory called cs61a to store all of the assignments for this class:

mkdir cs61a

A folder called cs61a will appear in our home directory.

Changing directories

To move into another directory, we use the cd command. Try typing the following command into your terminal:

cd cs61a

The cd command will change directories — in other words, it moves you into the specified folder. In the example above, we chose to move into the cs61a directory.

If we want to go back to our home directory, there are a few ways to do so:

  • Type cd .. (two dots). The .. means "the parent directory". In this case, the parent directory of cs61a happens to be our home directory, so we can use cd .. to go up one directory.
  • Type cd ~ (the tilde). Remember that ~ means home directory, so this command tells your terminal to change to the home directory, no matter where you currently are.
  • Type cd (that is, the cd command with no arguments), typing just cd is a shortcut for typing cd ~.

At this point, let's create some more directories. Make sure you are in the ~/cs61a directory, using the necessary cd commands. Then create projects and labfolders inside of our cs61a folder:

cd ~/cs61a
mkdir projects
mkdir lab

Now if we list the contents of the directory (using ls), we'll see two folders, projects and lab.

cs61a directory

Downloading the assignment

Next download the zip archive, lab00.zip, which contains all the files that we'll need for this lab. Once you've done that, let's find our downloaded file. On most computers, lab00.zip is probably located in a directory called Downloads in your home directory. Let's use the ls command to check:

ls ~/Downloads

If you don't see lab00.zip, ask a TA or lab assistant for help.

Extracting starter files

We'll then need to extract the files in the zip archive before we can start working. Different operating systems and different browsers have different ways of unzipping. If you don't know how, you can search onine

Using terminal or Gitbash, you can unzip from the command line (hooray!), you can use the unzip command:

unzip lab00.zip

Make sure you are in the Downloads directory in your terminal.

Once you unzip lab00.zip, you should have a new folder in called lab00 which contains the following files:

  • lab00.py: The template file you'll be adding your code to
  • ok: A program used to test and submit assignments
  • lab00.ok: A configuration file for ok

Moving files

Let's move our starter files into our new lab directory. From the terminal use the following command:

mv ~/Downloads/lab00 ~/cs61a/lab

The mv command will move the ~/Downloads/lab00 folder into the ~/cs61a/lab folder.

Now, go to the lab00 folder that we just moved. Try using cd to navigate your own way! If you get stuck, you can use the following command:

cd ~/cs61a/lab/lab00

We're ready to start editing a file. Don't worry if this seems complicated — it will get much easier over time. Just keep practicing! You can also take a look at our UNIX tutorial for a more detailed explanation of terminal commands.

Understand the question

Open up lab00.py in your text editor. You should see something like this:

def twenty_fifteen():
    """Come up with the most creative expression that evaluates to 2015,
    using only numbers and the +, *, and - operators.

    >>> twenty_fifteen()
return ______
return ((13 * 31 + 100) * 4) + 3

The lines in the triple-quotes """ are called a docstring, which is a description of what the function is supposed to do. When writing code in 61A, you should always read the docstring!

The lines that begin with >>> called doctests. Doctests explain what the function does by showing actual Python code: "if we input this Python code (the lines that say >>>), what should the expected output be (the lines underneath the >>>)?"

In twenty_fifteen,

  • The docstring tells us to "come up with the most creative expression that evaluates to 2015," but that we can only use numbers and arithmetic operators + (add), * (multiply), and - (subtract).
  • The doctest for twenty_fifteen() checks that no matter how we do our calculation, twenty_fifteen should return the number 2015.

You should never change the doctests in your assignments! The only part of your assignments that you'll need to edit is the code.

Write code

Once you understand what the question is asking, you're ready to start writing code! You should replace the underscores in return ______ with an expression that evaluates to 2015. What's the most creative expression you can come up with?

Run tests

In 61A, we will use a program called ok to test our code. ok will be included in every assignment in this class.

Back to the terminal! Make sure you are in the lab00 directory we created earlier (remember, the cd command lets you change directories).

In that directory, you can type ls to verify that there are the following three files:

  • lab00.py: the starter file you just edited
  • ok: our testing program
  • lab00.ok: a configuration file for OK

Now, let's test our code to make sure it works. You can run ok with this command:

python3 ok

If you are using Windows and the python3 command doesn't work, try using just python or py. If neither of those work, take another look at the video in the section on installing Python to make sure you are setting up your PATH correctly. Ask a TA or lab assistant for help if you get stuck!

Note: The first time you run OK, you will be prompted for your bCourses email. We use this information to associate your code with you when grading.

Every time you run OK, OK will try to back up your work. Don't worry if it says that the "Connection timed out." We won't use your backups for grading.

If you wrote your code correctly, we should see a successful test:

Assignment: Lab 0
OK, version v1.4.1

Running tests

Test summary
    Passed: 1
    Failed: 0
[ooooooooook] 100.0% passed

If you didn't pass the tests, ok will instead show you something like this:

Doctests for twenty_fifteen

>>> from lab00 import *
>>> twenty_fifteen()

# Error: expected
#     2015
# but got
#     ...

Test summary
    Passed: 0
    Failed: 1
[k..........] 0.0% passed

Fix your code in your text editor until the test passes.

Submitting assignments

Now that you have completed your first CS 61A assignment, it's time to turn it in.

Step 1: Submit with ok

From your terminal, make sure you are in the directory that contains ok. If you aren't there yet, you can use this command:

cd ~/cs61a/lab/lab00

Next, use ok with the --submit option:

python3 ok --submit

This will prompt you for an email address if you haven't run OK before, please use your berkeley email address. After that, OK will print out a message like the following:

Submitting... 100% complete
Backup successful for user: ...
URL: https://ok-server.appspot.com/#/...

You can follow the URL to view your submission.

Step 2: Verifying your submission

You can follow the link that OK provides to see your final submission, or you can go to okpy.org. You will be able to view your submission after you log in.

Make sure you login with the same email you provided when running ok from your terminal!

You should see a successful submission for lab00.

Congratulations, you just submitted your first CS61A assignment!