First Steps

This is Tier 0 — the beginning. It assumes you have never programmed before, in any language. By the end of these five chapters you'll have written and run real Python: doing arithmetic, building text, reading input from a person, and printing answers back.

Five chapters, in order:

What Python Is & Running Code — what a program is, what the Python interpreter does, and print — the command that lets a program talk back.
Variables & Basic Types — naming values so you can reuse them, and the four basic kinds of value: whole numbers, decimals, text, and true/false.
Numbers & Arithmetic — the maths operators, the two kinds of division, and why 0.1 + 0.2 isn't quite 0.3.
Strings, the Basics — building and reshaping text with f-strings and methods, and reading individual characters.
Input & Output — reading what a person types, converting it to a number, and writing a first interactive program.

Every code block with a ▶ Run button is live — click it, change the code, run it again. The fastest way to learn at this tier is to perturb working examples: change a number, swap a word, break something on purpose, and see what happens. You cannot harm anything; the worst case is an error message, and reading error messages is itself a skill these chapters build.

📘 How to read the Intuition boxes. Each one is built in three moves:

The mechanism — what the interpreter is actually doing.
A concrete bite — a specific, runnable way the naive assumption fails.
The earned rule — the decision heuristic, now justified rather than asserted, plus its cost.