Installing Python

Python is a program like any other, and it has to be installed before it can run your code. Until then, the instructions you write in Python are like notes left for a translator who has not arrived yet: perfectly good text, with nobody to read it. This page installs the current version, Python 3.15, from the official source on Windows or a Mac, and proves it worked with a single command.

This is one of the few pages in the book that names specific download pages and installers. Those details change more often than the language does, so if a screen looks slightly different from the description here, trust the official site and the version check at the end.

Where Python Comes From

Python is made by a community of volunteers and published by the Python Software Foundation at python.org. That is the only place this book downloads it from. Sites that offer a Python download with extra bundled software are best avoided, for the same reason you would avoid any installer from an unknown source.

Windows: the Python Install Manager

On Windows, Python is installed through the Python Install Manager, a small tool that installs Python versions and keeps them up to date. You can get it from the Downloads page at python.org, or from the Microsoft Store by searching for Python Install Manager. Both are published by the Python Software Foundation. Install it the way you would install any app.

Then open a new terminal and type python. If no version of Python is installed yet, the Install Manager installs the latest one automatically and starts it. During that first install it may offer to add a folder to your system path, the list of places Windows searches for programs. That step is optional; you can say no, and everything in this book still works.

If you type python and a Python prompt with three greater-than signs appears, type exit() and press Enter to leave it. The next topic explains that prompt properly.

You may see older guides that mention a different Windows installer and a command called py. The older installer is being retired after Python 3.15, and the Install Manager provides the py command too. In this book, on Windows, the command is simply python.

macOS: the python.org Installer

On a Mac, go to the Downloads page at python.org and download the macOS installer for Python 3.15. It is a package file ending in .pkg. Open it and click through the steps; the defaults are right.

On a Mac the command is python3, with the 3 on the end. There is a reason. Your Mac may already have an older copy of Python that came with Apple's developer tools, also called python3. After installing, open a new Terminal window: the new installation is found first, and the version check below tells you which one actually runs.

Linux, Briefly

Most Linux systems already include Python, because parts of the system itself are written in it. Check the version with the command in the next section. If it is older than 3.15, your distribution's package manager can usually provide a newer one. Almost everything in this book also works on Python 3.10 or newer; the few places where 3.15 behaves differently say so. Throughout the book, Linux readers follow the macOS commands.

Proving It Worked

Open a new terminal window and ask Python for its version. On Windows the command is python --version; on a Mac it is python3 --version. Two dashes before the word version, no space between them. The answer should start with Python 3.15.

PS C:\Users\you> python --version
Python 3.15.0

you@mac ~ % python3 --version
Python 3.15.0

The number after the second dot may be higher by the time you read this. That is fine: it only means a later bug-fix release. What matters is that it starts with 3.15.

If instead you see a message that the command was not found, the terminal could not find a program with that name. On a Mac the message reads: command not found, followed by the name you typed. The usual cause is simple: the terminal window was already open before the installation finished, and it does not know about the new program yet. Close it, open a new one, and try again. On a Mac, also check that you typed python3 and not python.

you@mac ~ % python --version
zsh: command not found: python