Python

From your first script to lists, dictionaries, classes and files, in Python 3.14.

Each lesson has runnable examples and exercises. Python is real (CPython 3.14), running in a small Linux machine inside this tab: no install, no server running your code. The first visit downloads about 12 MB, of which the first 4 MB before you can start; later visits start from your browser's copy.

Linux + Python 3.14 in your browser

Chapter 1 · Foundations

What runs your program; numbers, text, input and errors

1. 1 Hello, Python

   Your first program, the command that runs it, and print.

2. 2 Inside the computer

   What a computer is made of, what happens when your program runs, and where its values live in memory.

3. 3 Names and numbers

   Bind names to numbers, text and true/false, change them, and meet the two kinds of division.

4. 4 Text and input

   Join and format text with f-strings, and read what the user types.

5. 5 Reading errors and tracebacks

   Tell a syntax error from an exception, and read a traceback from its last line.

Chapter 2 · Decide, repeat, reuse

Decisions, loops, functions and modules

1. 6 Decisions and loops

   if, elif and else, for and while, the classic FizzBuzz, and a test of it all.

2. 7 Functions

   Name a piece of code, give it values, get one back, and see a frame per call.

3. 8 Modules and programs

   Use Python's built-ins and modules, write your own, and split a program into files.

Chapter 3 · Data

Text, lists, grids, dictionaries, sets and recursion

1. 9 Working with text

   Index, slice, split and join text, and format it into columns.

2. 10 Lists

   Keep many values in order, change them, and see when two names share one list.

3. 11 Tuples, loops and grids

   Pair values in tuples, loop with enumerate and zip, stop early, and walk a grid.

4. 12 Dictionaries and sets

   Look values up by key, count things, and keep unique values in a set.

5. 13 Comprehensions and sorting

   Build lists in one line, and sort anything by the key you choose.

6. 14 Recursion

   Solve a problem with a function that calls itself, and watch the frames pile up.

Chapter 4 · Objects and robust code

Classes, exceptions, generators, dataclasses and match

1. 15 Classes and objects

   Define your own kind of object with its data and its methods.

2. 16 Inheritance and special methods

   Build on a class, and teach your objects to print, compare and sort.

3. 17 Exceptions

   Catch what can go wrong, raise your own errors, and clean up.

4. 18 Iterators and generators

   See what a for loop really does, and make values only when they are asked for.

5. 19 Dataclasses, enums and match

   Shorter classes, named choices, and match to pick a case by its shape.

Chapter 5 · Real programs

Files, tested algorithms and a project of your own

1. 20 Files

   Read and write text, CSV and JSON files that outlive your program.

2. 21 Practice: searching, sorting and testing

   Search, sort and test by hand, then meet the tools real code uses.

3. 22 A project of your own

   Finish a small tool: a package that reads a CSV file, answers commands and prints a report.