Lab 0 Solutions
Community Building Exercise
At the beginning of class, you will be participating in several activities that introduce you to the community of CS 88—your TA and most importantly, your fellow classmates.
Set-up for Class
In c8 you are doing all your development in the cloud on datahub.berkeley.edu, but we will be using your personal computer for cs88. If you are using the instructional
machine in the lab you can ignore this section. We would like to be able to use the
datascience module in cs88 as well, to make the most of what you learn in c8 and
In c8, you mainly work in a python notebook: you type a piece of code into a cell, run the cell, and voila, the output is magically displayed. Furthermore, you can type text in addition to code in a python notebook; all the titles, subtitles, and instructions are text. However, more often in the real world you would be using a combination of terminal and text editor to run your program. And that’s what we will be doing in this class. All your code goes on to the text editor, and you run the code using Python on the terminal.
This lab explains how to use your own computer to complete assignments for CS 88. If you are using a school computer, most of the instructions are the same, except you won't have to install anything.
Install 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 88.
If you're on a Mac or are using a form of Linux (such as Ubuntu), you already have a program called
Terminalon your computer. Open that up and you should be good to go.
For Windows users, we recommend downloading a terminal called GitBash.
Install 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
pythoncommand from your terminal.
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
PATHenvironment variable; the same video describes how to do this from 5:00 to 5:54.
Install 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.
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:
Using the terminal
Terminal is a tool for you to interact with your folders and files. To open a terminal in datahub, click on “new” in the upper-right hand corner, and click on terminal.
When you open a terminal in datahub, it looks something like this:
You start off in something called your home directory.
Your TA will now demonstrate for you how to use the terminal. By the end, you should be able to answer these questions:
- 1.) What is a directory? A file?
- 2.) What does it mean by current directory?
- 3.) What are some basic commands I can use in terminal?
The most common terminal commands are as follows:
- ls - lists out all the files and directories in the current directory
- cd “folder name” - cd stands for “change directory”. cd “folder name” gets you into the directory with the folder name, provided the folder is inside your current directory
- cd.. - exit out to the previous directory
- cd - exits out to home directory
- mkdir - “make directory”, or create a folder
- touch - make a file
- clear - clear previous commands to make terminal look cleaner
All macs automatically come with a terminal. Open it up and play around with it. It looks something like this. You should see a tilde sign (~), which means that you are in your home directory:
If you are using Window, please follow the instructions to download git bash here:
Head to this website and click the windows download link.
You should be able to install Git Bash with most of the default configuration options, with one exception. In the Configuring the terminal emulator to use with Git Bash step, select the second option: Use Windows' default console window.
- Make a directory called "cs88"
cdinto that directory, and make 3 more directories: "labs", "hw", "projects"
We can use the terminal to check if your Python 3 interpreter was installed correctly. Try the following command:
If the installation worked, you should see some text printed out about the
interpreter followed by
>>> on its own line. This is where you can type in Python
code. Try typing some expressions you saw in lecture, or just play around to see
what happens! You can type
Ctrl-D to return to your command line.
- If the
python3command doesn't run at all:
- If Python freezes (doesn't display anything at all):
You probably didn't select the "Use Windows' default console window" option when installing Git-Bash manually. Try
winpty python, or just uninstall Git-Bash and reinstall it with the correct options.
- If you see an error like
WindowsApps/python: Permission denied:
Go to the
WindowsAppsfolder whose path is shown, and rename
python.bak.exe(and similarly, rename
python3.bak.exe), then try again.
- If Python doesn't run at all, and you used our automated installer:
Go back and try installing using the manual method.
- If Python doesn't run at all, and you installed manually:
Make sure you set up your "PATH" correctly as shown above.
- If you mixed multiple versions of Python (e.g. 32-bit and 64-bit, or 3.6 and 3.8, etc.):
They may conflict. Occasionally, this becomes extremely difficult to fix—even for instructors.
Uninstall them one-by-one (the most recent one first), then reinstall only the latest 64-bit version.
Ask for help if you get stuck!
Organizing your files
There are many terminal commands that you will be using in this course.
The first command we'll use is
ls. Try typing it in the terminal:
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
cs88 to store all of
the assignments for this class:
A folder called
cs88 will appear in our home directory.
To move into another directory, we use the
cd command. Try typing the
following command into your terminal:
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
If we want to go back to our home directory, there are a few ways to do so:
cd ..(two dots). The
..means "the parent directory". In this case, the parent directory of
cs88happens to be our home directory, so we can use
cd ..to go up one directory.
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.
cd(that is, the
cdcommand with no arguments), typing just
cdis a shortcut for typing
At this point, let's create some more directories. Make sure you are in
~/cs88 directory, using the necessary
cd commands. Then create
labfolders inside of our
cd ~/cs88 mkdir projects mkdir lab
Now if we list the contents of the directory (using
ls), we'll see two
Downloading the assignment
Next download the zip archive, lab00.zip, if you have not already done so. This zip file contains all the files that we'll need for this lab.
Uploading the assignment
The lab must be uploaded to Jupyter as a zip file; uploading a folder will not work. Switch from the terminal to the homepage and upload the zip file into the
cs88 directory you created earlier.
Extracting starter files
Switch back to the terminal tab.
Use the command below to unzip the file.
Make sure you are in the
cs88directory in your terminal.
Once you unzip
lab00.zip, you should have a new folder called
cs88 directory 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
You no longer need
lab00.zip and can delete it from your
cs88 folder if you want.
You're now ready to start looking at the code! 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.
Floating point numbers (floats) behave a lot like real numbers. You can identify a float by the decimal point. All floats have decimal points. To write a floating point number (as a literal) you must add a decimal point!
>>> 3.141592 3.141592 >>> 2*3.141592 # you can mix ints and floats 6.283184 >>> pie = 3.141592 # you can assign values to variables >>> pie 3.141592 >>> pie/pie 1.0 >>> pie/pie == 1 # a float can be equal in value to an int True >>> from math import pi # here is a better pi >>> pi 3.141592653589793 >>> 5.0/3.0 # this is division of floats, not ints 1.6666666666666667 >>> 2**(1/2) # square root - isn't that transcendental? 1.4142135623730951
Expressions follow operator precedence (just like in math). Operations are performed one at a time in a specific order. Parenthesis are used to specify order (again, just like in math - remember PEMDAS?).
>>> 2 + 3 - 4 + 5 # equal precedence, left to right 6 >>> 2 + 3 - (4 + 5) # order matters - parentheses are your friend -4 >>> (((2 + 3) - 4) + 5) # explicit order of the first example 6 >>> 2 + 3 * 4 # * and / bind more tightly than + or - 14 >>> 2 + (3 * 4) 14 >>> (2 + 3) * 4 20 >>> 2 + 3 / 4 * 5 # what about * and / ? 5.75
An expression can have multiple return values, called a tuple:
>>> 2, 3 (2, 3) >>> x, y = 1, pi >>> y 3.141592653589793
Doing the assignment
Question 1: Twenty Twenty
lab00.py in your text editor. You should see something like this:
def twenty_twenty(): """Come up with the most creative expression that evaluates to 2020, using only numbers and the +, *, and - operators. >>> twenty_twenty() 2020 """return ______return 2000 + 20
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 CS 88,
you should always read the docstring!
The lines in the docstring that begin with
>>> are called doctests.
Doctests explain what the function does by showing actual Python code.
The lines underneath the
>>> show the expected output from running the above Python code.
- The docstring tells us to "come up with the most creative expression that
evaluates to 2020," but that we can only use numbers and arithmetic operators
- The doctest for
twenty_twenty()checks that no matter how we do our calculation,
twenty_twentyshould return the number 2020.
You should never change the doctests in your assignments! The only part of your assignments that you'll need to edit is the 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 2020. What's the most creative expression you can come up with?
- Open lab00.py in your text editor. Start by simply returning 2020. This is not very creative, but it gives the right answer.
Run Python on your code in lab00.py using the interactive flag. When you get the prompt, type the name of the function, just like in the doc string. Did you get the right answer?
python -i lab00.py >>> twenty_twenty() 2020 >>> exit()
- Exit Python to get back to your terminal shell. You will need to do that each time you run Python interactively.
You are going to want to learn to test your code before submitting it to the autograder. This always begins with reading it, thinking about it and convincing yourself it should work. Come up with examples that verify it really does what it should. That is what goes into the docstring.
In CS 88, 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
In that directory, you can type
ls to verify that there are the following
lab00.py: the starter file you just edited
ok: our autograder
lab00.ok: a configuration file for OK
Now, let's test our code to make sure it works. You can run
ok with this
python3 ok --local
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_twenty >>> from lab00 import * >>> twenty_twenty() 2013 # Error: expected # 2020 # but got # ... --------------------------------------------------------------------- Test summary Passed: 0 Failed: 1 [k..........] 0.0% passed
Fix your code in the text editor until the test passes.
Submitting the assignment
Now that you have completed your first CS 88 assignment, it's time to turn it in. Note that it is not sufficient to receive credit for an assignment simply by running the autograder per the last section. You must follow these steps to submit and get points!
Step 1: Submit with
In your terminal, make sure you are in the directory that contains
you aren't there yet, you can use this command:
ok with the
python3 ok --submit
This will prompt you for an email address if you haven't run Ok before. Please follow these directions, and refer to the troubleshooting steps on that page if you encounter issues. After that, Ok will print out a message like the following:
Submitting... 100% complete Backup successful for user: ... URL: https://okpy.org/...
Step 2: Verify your submission
You can follow the link that Ok printed out 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 log in with the same email you provided when running
okfrom your terminal!
You should see a successful submission for Lab 0.
Congratulations, you just submitted your first CS 88 assignment!
You can use the
--helpflag to get more information on Ok:
python3 ok --help
This flag works just like it does for UNIX commands we used earlier.
Appendix: Useful Python command line options
When running a Python file, you can use flags on the command line to inspect your code further. Here are a few that will come in handy. If you want to learn more about other Python flags, take a look at the documentation.
Using no flags will run the code in the file you provide and return you to the command line.
-ioption runs your Python script, then opens an interactive session. To exit, type
exit()into the interpreter prompt. You can also use the keyboard shortcut
Ctrl-Don Linux/Mac machines or
Ctrl-Z Enteron Windows.
If you edit the Python file while running it interactively, you will need to exit and restart the interpreter in order for those changes to take effect.
python3 -i lab00.py
-m doctest: Runs doctests in a particular file. Doctests are marked by triple quotes (
""") and are usually located within functions.
python3 -m doctest lab00.py
Congratulations on finishing your first lab! And welcome to CS 88.