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CAPP Camp 2022

Run Python Programs

In this section, you will walk through the steps to edit and run a Python program.

Use an Editor

Let’s start by editing a text file. List the files in the lab1 directory. You should see the following:

backups hello_world.py  my_echo.py  my-input.txt  test.txt

How do we view and edit the contents of these files? There are many high-quality text editors for Linux. We will use Visual Studio Code, which is good for writing code.

You can open a specific file, say test.txt, using the code command from the Linux command-line by typing:

code test.txt

Specifically, you’ll see the following text:

Lab 1 Test file
===============

Author: Firstname Lastname

If the file is blank, close it and ensure that test.txt exists in your local directory (use ls to list the files in your local directory). If it does not, use cd to navigate to the lab1 subdirectory inside the lab1_linux_remote directory.

For now, we will use VS Code in a very basic way. You can navigate to a particular place in a file using the arrow keys (or your mouse) and then type typical characters and delete them as you would in a regular text editor. You can save your changes using the save option in the file menu or use the keyboard shortcut Crtl-s.

Checkpoint

  1. Add your name after Author: in this file.

  2. Save the file.

  3. Close and reopen the file, ensuring that your name is still there.

Run a Python Program

python3 file.py Runs the Python program file.py.

In CAPP 30121, you will learn Python. To run a Python program, use the command python3 and the name of the file that contains your program.

Use ls to verify there is a file named hello_world.py in your lab1 directory. Now, run the program in hello_world.py by typing:

python3 hello_world.py

This program is very simple. It just prints “Hello, World!” to the screen.

Exercises

In this section you will modify and re-run the program in hello_world.py. This change is very simple but goes through all the mechanical steps needed to program.

Open the file hello_world.py with the command:

code hello_world.py

The file contains a single line of code:

print("Hello, World!")

Change this line so that it instead says “Hello, “ and then your name. For example if your name were Gustav Larsson, the line would read:

print("Hello, Gustav!")

Once you are finished with your edits, save the file and rerun the program using python3. Confirm that “Hello, “ followed by your name and an explanation point, are printed in the terminal.

–

Let’s recap the steps to programming in Python with the terminal:

  1. Change your .py file with an editor.

  2. Save the file.

  3. Run the file with python3.

Forgetting to save the file (step 2) is a very common mistake!

In addition to the command-line version of Python, programmers often use Jupyter notebooks and other interactive versions of Python. You will be using ipython3, an interactive version of the Python interpreter, later in CAPP 30121.

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