Lab 0 Solutions

Important Notes

Data 8 vs C88C

In Data 8 you are doing all your development in the cloud on datahub.berkeley.edu, but we will be using your personal computer for C88C.

In C8, you mainly work in a Python (Jupyter) 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. This splits the process of writing code and running the code — you use a text editor to write your code and then you run your code using Python on the terminal.

Task: Setup

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 C88C.

Install Python 3

Python 3 is our primary programming language. Download the correct version of Python (3.11.5) for your operating system (Mac, Windows, Linux) here.

Important: Python 3.11.x is strongly recommended for this class. Notably, Python 3.12+ will NOT work (okpy will break with a urllib3 ModuleNotFound error).

Next, follow the instructions for your specific operating system below.

Optional info about Python versions: There are 2 major versions of Python in use today: Python 2 and Python 3. In this class, and in most modern applications, we use Python 3 (so when we say "Python" in this class, we really mean "Python 3"). Python 3 is not backwards compatible with Python 2. However, some legacy applications may still use Python 2, which has slightly different syntax and functionality. For example, Python 2 comes preinstalled on Mac, but we want to install Python 3.

python3 --version

Python 3.XX.XX

python3 --version

Python 3.XX.XX

Install a text editor

Your computer's terminal combined with the Python 3 you just installed 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 (including files that contain code), 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 highly recommend for this class you use Visual Studio Code, aka VS Code. Visual Studio Code is a full-featured desktop editor with many extensions available to support different languages, and is widely used by course staff.

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!

Highly Recommended: Turn on Auto Save

To avoid the problem explained above, turn on auto-save in VS Code so that your changes are automatically saved to the file. You can do this by going to File > Auto Save.

Optional: Pair Programming Using VS Code Live Share

Throughout this course, you will have many chances to collaboratively code with others in labs and projects. We recommend you download VS Code's Live Share extension to help with this: It's like Google Docs, but for writing code!

Using the terminal

Terminal Walkthrough

Note: If you are already familiar with the terminal, directories, file paths, etc. you can skip this section. Otherwise, click below to learn more.

Note: While you aren't expected to memorize terminal commands and they will not be tested, you are expected to have a basic understanding of the terminal, directories, file paths, etc. for the purpose of completing coding assignments. Knowing how to work with the terminal is also a very important skill for any data/computer scientist.

~
|-------Desktop
|        |
|        |-------Screenshots
|                   |-----------a.png
|                   |-----------b.png
|-------Downloads
|        |-------c.txt

Task: Creating a c88c directory

Follow the instructions below to set up the directories you'll need for coding assignments.

1. Open the terminal for your computer.

2. Go into your Desktop:

   cd ~/Desktop

3. Create a new directory called c88c:

   mkdir c88c

4. Go into the c88c directory you just made:

   cd c88c

5. Create 3 directories for the 3 types of coding assignments you'll do in this class:

   mkdir labs hw projects

Note: Technically you are not required to put your c88c directory in your desktop, but we recommend this because it's easy to access. Feel free to move it as long as you know how to navigate to it in the future.

CLI vs GUI

Remember that you can access the files and directories (folders) on your computer in two different ways. You can either use the terminal (which is a command line interface or CLI) or you can use a file explorer such as Finder (Mac) or File Explorer (Windows). Both are examples of a graphical user interface (GUI). The techniques for navigating are different, but the files are the same. For example, here's how the labs folder might look ike on each operating system.

Click to toggle▼

Here's how the folder looks in Finder on Mac:
And here's how the exact same folder looks in terminal:

Notice the red box shows you the path in both cases, and the blue ellipse shows you the contents of the labs folder.

Note: At this point your labs folder is empty, but eventually it will contain folders for each lab assignment like in the screenshot above.

Click to toggle▼

Here's how the folder looks in File Explorer on Windows:

And here's how the exact same folder looks in PowerShell (a terminal for Windows):

The contents of the c88c folder can be found listed in the GUI, and underneath the ls command in the CLI.

Note: At this point your labs folder is empty, but eventually it will contain folders for each lab assignment like in the screenshot above.

VS Code Integrated Terminal

As you work on coding assignments in this course, you will often find yourself switching back and forth between writing code and running code. To make things easier, you do not need to open your terminal app and text editor separately — you can have everything in one window. The following instructions are applicable to VS Code (the recommended editor), but most editors have a similar integrated terminal feature.

1. Open VS Code
2. At the top menu bar (e.g. where it says File, Edit, Selection, etc.), go to File > Open.
3. Navigate to your Desktop and click on the c88c folder you just created. Then click Open. (This will open the c88c folder in VS Code so that you can edit files in that directory. Right now there are no files, just directories.)
4. At the top menu bar, go to Terminal > New Terminal. It should open a mini terminal window inside your VS Code window.

Python Basics

Python Interpreter

Throughout the course, you may want to try running small bits of Python code and see what gets returned or printed. You can do this using the Python Interpreter, which comes with your installation of Python 3. The way you interact with the Python Interpreter is more or less the same way you interact with code cells in a Jupyter notebook from Data 8.

Follow along with the walkthrough below in your own terminal.

Run the following command in your terminal:

python3

If the Python 3 installation worked, you should see something similar to this:

Python 3.11.4 (main, Jan 20 2024, 17:35:35) [Clang 14.0.0 (clang-1400.0.29.202)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 

When you see the >>>, this means the Python Interpreter is ready to accept Python code you type into it.

Windows Troubleshooting

Intro to Python Syntax

Follow along on your own Python Interpreter with the Python expressions below.

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
>>> x
1
>>> y
3.141592653589793

Exiting the Python Interpreter

You can type exit() or press Ctrl + D to exit the Python Interpreter and return to your command line. It looks something like this (on the Mac Terminal):

Task: Doing the assignment

Downloading the assignment

1. Download the starter code for the assignment, if you haven't already. You can either click on the lab00.zip button at the very top of the page, or click lab00.zip.
2. Move the lab00.zip file into your ~/Desktop/c88c/labs directory. You can do this by dragging and dropping it using Finder (Mac) or File Explorer (Windows), or the mv command in the terminal (if you know how).

3. Unzip the file, if you haven't already. If the file is zipped, it should be called lab00.zip and look like a single file. In this case, follow the steps below to unzip it. Otherwise, it should be called lab00 and look like a directory. In this case, move on to step 4.

   1. On Mac, in Finder, you can just double click the lab00.zip file.
   2. On Windows, in File Explorer, right click the lab00.zip file and click Extract All.
4. Delete the zip file. Once you have unzipped it, you no longer need the zip file.

5. Open the c88c directory on VS Code, if you don't already have it open. If you look on the left sidebar and click on the icon that looks like 2 pieces of paper (top left), it will open the Explorer which lets you view the files and directories in c88c. If you click on the labs directory, you should now see a directory called lab00 inside. Then, if you click on the lab00 directory, you should see 3 files:

   • lab00.py: The Python file (notice that the file extension is .py) you'll be writing code in
   • ok: A program called OkPy used to test if you wrote code correctly (do not open/modify this)
   • lab00.ok: A configuration file for OkPy (do not open/modify this)
   • See the next sections for screenshots on what this looks like if you're confused.

Workflow overview

For each assignment, we'll provide you with some starter code (for example, lab00.py); all you have to do is fill in the parts that are incomplete.

Open lab00.py in your text editor of choice. To do this on VS Code, open the Explorer tab, navigate to the lab00.py file (it's inside labs/lab00) and then click on lab00.py. Clicking on it will open the file in a new tab in the center of your screen on VS Code.

We highly recommend having your text editor and terminal open at the same time. This will allow you to write code and test it without having to switch windows. See VS Code Integrated Terminal if you haven't already for instructions on how to do this.

Here's a screenshot of a typical workspace, which uses VS Code and its integrated terminal on MacOS, and is from the year 2023. Your setup will look slightly different but it should be very similar.

Question 1: Twenty Twenty Four

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

def twenty_twenty_four():
    """Come up with the most creative expression that evaluates to 2024,
    using only numbers and the +, *, and - operators.

    >>> twenty_twenty_four()
    2024
    """
    return ______
    return 2 * 1000 + 24

Functions

• The starter code contains the skeleton for a function, which you can think of as similar (but not exactly the same) as a function in mathematics: It can have an input and output. In this case, the keyword def tells us we are defining a function called twenty_twenty_four which takes in no inputs since there is nothing between the parentheses after the function name.
• Functions can be used, or called, by writing the name of the function and a set of parentheses, with its inputs inside the parentheses.

Docstring

• 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 C88C, you should always read the docstring!
• The docstring for this function tells us to "come up with the most creative expression that evaluates to 2024," but that we can only use numbers and arithmetic operators + (add), * (multiply), and - (subtract).

Doctest

• The lines in the docstring that begin with >>> are called doctests. Doctests explain what the function is supposed to do by showing actual Python code.
• The lines underneath the >>> show the expected output from running the above Python code in the Python Interpreter, assuming the function has been defined.
• The doctest for this function checks that no matter how we do our calculation, calling the function twenty_twenty_four should output, or return, the number 2024.

Writing code

Once you understand what the question is asking, you're ready to start writing code!

Below is an example of how to write and test your code manually (later we will show you how to run the autograder tests with OkPy).

1. Open lab00.py in your text editor.
2. Replace the underscores in return ______ with an arithmetic expression that evaluates to 2024. It can be as simple or complex as you wish — we are only going to test that it evaluates to 2024.

3. In your terminal, ensure that you are in the lab00 directory. If you're currently in the c88c directory, you will need to run:

   cd labs/lab00

4. Once you are in the lab00 directory, run the following command. NOTE: If you're on Windows and ran into issues with using the python3 command but other commands worked (e.g. python, py, py3, etc.), you should use those instead from now on in all assignments wherever it says to use python3.

   python3 -i lab00.py

This should open the Python interpreter. Notice that we added -i to the python3 command. The -i is called the "interactive flag" because it loads and runs the code in the file you gave it (lab00.py) and then allows you to enter more Python code in the interpreter. This will allow you to call the function in the Python interpreter and it should display 2024.

>>> twenty_twenty_four()
2024

On the other hand, if you just entered python3 in the terminal and then tried to call the function, it would give you an error like the one below since it doesn't recognize your function (it hasn't been loaded).

>>> twenty_twenty_four()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'twenty_twenty_four' is not defined

Additionally, if you omitted the -i and ran python3 lab00.py in the terminal, it would ONLY run the lab00.py file and not open a Python Interpreter. It will not display any output and immediately return to the terminal (since in the file you didn't call the function, you only defined it).

Once you're done testing, exit the Python Interpreter to get back to your terminal shell (enter exit()). You will need to do that each time you run Python interactively.

Troubleshooting Tests (for both manual and autograder tests)

  File "", line 1
    >>> twenty_twenty_four()
    ^^
SyntaxError: invalid syntax

Running Autograder (OkPy) Tests

In C88C, we will use a program called ok (OkPy) to test our code. ok will be included in every assignment in this class.

1. In the (integrated) terminal, make sure you are in the ~/Desktop/c88c/labs/lab00 directory by using pwd to display the absolute path of the directory you're currently in. If you are not, use the cd command to change directories:

   cd ~/Desktop/c88c/labs/lab00

2. Run the ok autograder tests for the function we just wrote:

   python3 ok -q twenty_twenty_four

3. If this is your first time running an OkPy test, it will ask you to enter your @berkeley.edu email. You should do this and press Enter. It will then open a new tab on your browser to log in to the okpy.org website. Click Confirm. This will then bring you to your okpy.org dashboard. You can close this tab and go back to the terminal.

If you wrote your code correctly, you should see a successful test output similar to the one below:

=====================================================================
Assignment: Lab 0
OK, version v1.18.1
=====================================================================

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Running tests

---------------------------------------------------------------------
Test summary
    1 test cases passed! No cases failed.

Backup... 100% complete
Backup successful for user: oski@berkeley.edu
URL: https://okpy.org/cal/cs88/sp24/lab00/backups/abc123

OK is up to date

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

=====================================================================
Assignment: Lab 0
OK, version v1.18.1
=====================================================================

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Running tests

---------------------------------------------------------------------
Doctests for twenty_twenty_four

>>> from lab00 import *
>>> twenty_twenty_four()
2014

# Error: expected
#     2024
# but got
#     2014

---------------------------------------------------------------------
Test summary
    0 test cases passed before encountering first failed test case

Backup... 100% complete
Backup successful for user: oski@berkeley.edu
URL: https://okpy.org/cal/cs88/sp24/lab00/backups/abc123

OK is up to date

Fix your code in the text editor until the test passes. See the Troubleshooting Tests section just above this section if you're having trouble.

Task: Submitting the Assignment

Now that you have completed your first C88C assignment, it's time to turn it in. You can follow these next steps to submit your work and get points.

1. Log in with School Credentials using your CalNet ID to Gradescope. You’ll be taken to your Dashboard as soon as you log in.

   

2. On your Dashboard, select the course C88C. You should have already been added to Gradescope. If this is not the case, please make a private Ed post. This will take you to the list of assignments in the course that you’re able to submit. On this list, you will see the status of the assignment, the release date, and the due date.
3. Click on the assignment to open it.

4. When the dialog box appears, click on the gray area that says Drag & Drop. This will open your file finder and you should select your code file (example: lab00.py) that you edited for this assignment.

   
   

5. Once you’ve chosen your file select the Upload button. When your upload is successful, you’ll see a confirmation message on your screen and you’ll receive an email confirmation.

   
6. Wait a few seconds for the autograder to grade your code file. Note that the screenshot is from 2023, but your year will be different.

🎉🎉 Congratulations on finishing your first lab and welcome to C88C. We hope this will be a rewarding semester!

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.

  python3 lab00.py

• -i: The -i option runs your Python script first, then opens an interactive session. To exit, type exit() into the interpreter prompt. You can also use the keyboard shortcut Ctrl-D on Linux/Mac machines or Ctrl-Z Enter on 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. If there is no output, it means all doctests passed. Doctests are marked by triple quotes (""") and are usually located within functions. DO NOT DELETE DOCTESTS ON YOUR LABS AND HOMEWORKS. The autograder (OK) will not run properly without them.

  python3 -m doctest lab00.py

Python Tutor

Python Tutor is a website that allows you to write Python code in your web browser and see it visualized step by step. This is a super useful tool that can help you understand exactly what your code is doing and also keeps track of what variables’ values are along the way. If you ever have trouble understanding what your code is doing, or finding a bug, pull up python tutor and step through it!

(Optional) Text Editor Guides

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

• VS Code: A text editor with a graphical user interface.
• Emacs: A command-line editor.
• Vim: A command-line editor.

Common issues / FAQs

Click the questions to toggle showing/hiding the answers.

1. How to exit the Python interpreter?▼

You can type exit() or Ctrl + D to return to your command line. It looks something like this:

Note: Any code you write in the Python Interpreter is NOT saved. When you exit, everything will be lost. When writing code for assignments, you should write your code directly into the Python files. However, for testing or debugging you may want to use the Python Interpreter which is why we show you how to use it here.