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Chapter 0

Before you start: programs, files, and the terminal

On the left, a text file called hello.py holding two print lines; an arrow labelled python hello.py leads to a box labelled CPython, the interpreter, which reads the file and follows it step by step; a second arrow leads to a command window that shows the folder it is standing in, then Hello, world! and Ready!
You write the text. The interpreter reads it and follows it. A typed command starts it, from the folder that holds the file.

From a Text File to a Running Program

The app that tells you when the next bus comes started life as text files. So did the scripts that keep an online shop stocked and the tools scientists use to clean their data. So did much of the software behind the AI systems in the news. Someone typed instructions in a programming language, and a program called an interpreter read those instructions and carried them out. This course teaches you to write those instructions in Python 3.14, a language known for reading almost like plain English.

You don't need any programming experience, and you don't need to have typed commands into a computer before. This chapter covers the three things every later chapter takes for granted.

The first section explains what a program is. It covers the readable text you write (source code), the helper program that reads and carries it out (the interpreter), and the quick translation Python makes first, behind the scenes. You'll read short Python programs and say exactly what they print. You'll see how "interpreted" differs from "compiled". And you'll learn to tell from an error report whether your program never started or stopped partway through.

The second section gets you comfortable with files, folders, and paths, and with the window where you type commands instead of clicking. You'll make the folder your first Python file goes into. You'll learn why Python can only find a file from the right folder, and how to tell from a command's reply and its exit status whether it worked. Pick your operating system once and every set of steps follows your choice.

The third section explains how the course itself works. It covers the two ways each idea is explained and the kinds of exercises. It also draws the line between what a lesson page checks and what only your own computer (or Google Colab) runs. And it explains why every output and error report shown on a page is real, captured from Python 3.14 when the course was built.

By the end you'll have a folder waiting for hello.py, and a clear picture of what happens when you type python hello.py in it.

  1. 0.1Programs, source code, and the interpreter ~25 min
  2. 0.2Files, folders, and the terminal ~30 min
  3. 0.3How this course works ~20 min
  4. ✓Chapter wrap-up and review
Start with 0.1 → Chapter quiz
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