Setup and the First Script

It is 3:14 AM and the alert channel is already lit up: srv-07 is at 96% and climbing. You open the terminal on your own laptop to check it, and the machine answers command not found. You cannot debug a server from a machine that has never run a line of Python.

Before the platform, there is the machine in front of you. Ten minutes from now it will have an interpreter, an editor, and one script that proves both are working.

Python is the program that reads your .py file and executes it. Download the installer for your operating system from python.org/downloads; take the latest 3.x release, not a 2.x one.

On Windows, the first installer screen has a checkbox labelled Add python.exe to PATH. Tick it before pressing Install. If you miss it, run the installer again, choose Modify, and add it. On macOS, run the .pkg installer and accept the default destination. Linux usually ships with Python 3 already installed.

Open a terminal — Terminal on macOS or Linux, PowerShell on Windows — and ask the interpreter for its version:

python3 --version

On Windows the command is usually python --version. The reply should look like Python 3.12.4. Any 3.11 or newer is fine for this course.

Watch out: The Trap

• command not found after a successful install means the terminal was already open before the PATH changed. Close it, open a new one, try again.
• Python 2.7 is not the interpreter this course runs on. If python --version answers 2.7, use python3.
• Do not install a stub from an app store. Use the official installer so the command and pip are real.

A .py file is plain text. A word processor is the wrong tool: it inserts curly quotes and hidden formatting, and Python stops with SyntaxError on the first line it cannot parse.

Install Visual Studio Code from code.visualstudio.com. It is free, and it treats the folder you open as a project instead of treating each file as a document. After it launches, open the Extensions panel and install Microsoft’s Python extension; it gives you syntax colouring, error squiggles, and a terminal in the same window.

Create a folder for the course, for example ops-console, and open that folder in VS Code. Add a file named hello.py. The .py extension is what tells the editor — and you — that this file is Python.

print() writes its argument to the terminal and starts a new line. Text inside quotes is a string literal: the quotes mark where the text starts and stops, and they are not printed. A call with no matching quote is a syntax error before anything runs.

print("Hello, ops console")

Save the file. Open the integrated terminal with Ctrl+` (Cmd+` on macOS) and run it by name:

python3 hello.py

On Windows, use python hello.py. The terminal should answer:

Hello, ops console

That is the whole loop: edit the file, save it, run it, read what came back. Every later week is the same loop with more interesting files.

Watch out: The Trap

• can't open file 'hello.py' means the terminal is in a different folder. Run pwd (macOS/Linux) or cd (Windows) to see where you are, then cd into ops-console.
• print(hello) without quotes asks Python for a variable named hello. It has never been assigned, so the answer is NameError, not the word.
• A missing closing quote, or a curly quote from a word processor, raises SyntaxError before the first line executes.

Reading about setup is not setup. The console below runs Python in your browser, so it can prove the language works; running the same code in your own terminal proves your installation works. Do both.

The scaffold prints a placeholder. Replace it so the program prints the confirmation phrase named in the comment, run it here, then save the same two lines into hello.py and run them locally.

If both consoles answer with the confirmation line, the toolchain is complete: interpreter, editor, and a file that runs. That is the baseline every later lesson assumes.

The servers can wait another ten minutes. Your machine now has an interpreter, an editor that saves plain text, and one script that goes from file to terminal and back. Next week you hold two numbers, divide them without lying about their types, and print a status line worth pasting into the incident ticket.