Installing and Setting Up Python

Installing and Setting Up Python#

This book is terminal-centric by design. We believe that learning to work at the command line from the start builds habits that will serve you throughout your career. That means we deliberately de-emphasize graphical IDEs and point-and-click installers. The terminal is where programmers live, and this chapter gets you set up there.

Note

Recommended platforms: macOS and Linux. Both provide a Unix-compatible shell experience out of the box. Windows can work, but only via the Windows Subsystem for Linux (WSL). If you are on Windows, read the Windows section below first, then follow the Linux instructions.

We target Python 3.12 or later throughout this book.

Windows: Use WSL#

Windows does not ship with a Unix-compatible shell, and the native Windows command prompt (cmd.exe) or PowerShell behave differently enough from a Unix terminal that following along becomes unnecessarily difficult. The solution is the Windows Subsystem for Linux (WSL), which runs a real Linux environment directly on Windows — no virtual machine required.

We recommend WSL 2 with the Ubuntu distribution. Microsoft provides official setup instructions here:

The short version: open PowerShell as Administrator and run:

wsl --install

This installs WSL 2 and Ubuntu by default. Once installation completes and you have rebooted, launch Ubuntu from the Start menu. You will be dropped into a Bash shell inside a real Ubuntu environment.

From that point forward, follow the Linux instructions below exactly as written. Everything will work the same way.

macOS#

macOS ships with Python 3 pre-installed, but Apple’s bundled version is often out of date and tied to system tools — not ideal for coursework. We recommend one of the two approaches below.

Option A: Install Python via Homebrew (recommended)

Homebrew is the standard package manager for macOS. If you do not already have it, install it by running this command in your terminal:

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

Follow the prompts. Once Homebrew is installed, install the latest Python 3:

brew install python

Verify your installation:

python3 --version

Output should show Python 3.12 or later:

Python 3.x.x

Option B: Use the python.org installer (no Homebrew)

Download the macOS installer for the current Python 3 release from:

Run the .pkg file and follow the installer. When it completes, open a new terminal window and verify:

python3 --version

Output should show Python 3.12 or later:

Python 3.x.x

Either way, once you have Python 3.12 or later installed, continue to the Virtual Environments section below.

Linux#

Most Linux distributions include Python 3, but it may not be 3.12. Use your distribution’s package manager to install the right version.

Ubuntu / Debian:

sudo apt update
sudo apt install python3 python3-venv python3-dev

Note

On older Ubuntu releases (22.04 and earlier) the default python3 may be below 3.12. Check with python3 --version and, if needed, install a newer version via the deadsnakes PPA.

Fedora / RHEL / CentOS:

sudo dnf install python3

Arch Linux:

sudo pacman -S python

(Arch typically ships the latest stable Python.)

Verify after installation:

python3 --version

Output should show Python 3.12 or later:

Python 3.x.x

Virtual Environments#

Regardless of your platform, you should always work inside a virtual environment rather than installing packages into the system Python. A virtual environment is an isolated copy of Python with its own package directory. This keeps your projects independent from each other and from the system.

Creating a virtual environment

Navigate to the directory where you want to keep your coursework and create a virtual environment named .venv:

python3 -m venv .venv

This creates a .venv/ subdirectory containing a private Python interpreter and package directory.

Activating the virtual environment

You must activate the virtual environment every time you open a new terminal before doing any Python work for this course.

On macOS and Linux (including WSL):

source .venv/bin/activate

Your prompt will change to show the environment name:

(.venv) $

On Windows (only if using native PowerShell, not WSL):

.venv\Scripts\activate

Verifying the environment

With the environment active, confirm that Python and pip point into the virtual environment:

which python
python --version

Output:

/path/to/your/coursework/.venv/bin/python
Python 3.x.x

Deactivating

When you are finished working, you can deactivate the environment:

deactivate

Note

Activate before you work. Every time you open a new terminal session, run source .venv/bin/activate before running any Python commands for this course. Forgetting to activate is the most common source of “but it worked before!” confusion.

Alternative: Using uv#

uv is a fast Python package and project manager written in Rust. It can install Python itself, create virtual environments, and manage packages — all in one tool, and dramatically faster than pip. It also solves the version-selection problem cleanly: you tell uv which Python version you want and it handles the rest, no matter what the system default is.

uv requires Homebrew on macOS. On Linux (and WSL) it has its own installer script.

Installing uv

On macOS (requires Homebrew):

brew install uv

On Linux and WSL:

curl -LsSf https://astral.sh/uv/install.sh | sh

Restart your terminal (or run source ~/.bashrc) after the Linux install so that the uv binary is on your PATH.

Installing Python 3.12 with uv

uv can download and manage Python versions independently of the system:

uv python install 3.12

Creating a virtual environment with uv

uv venv --python 3.12 .venv

This creates the same .venv/ directory as before, but lets you specify the Python version directly — no need to worry about what python3 points to on your system. Activate it exactly as before:

source .venv/bin/activate

Installing packages with uv

Once the environment is active, use uv pip in place of pip:

uv pip install <package-name>

Note

For this course the standard venv and pip approach taught above is perfectly fine. uv is worth knowing about, but adds an extra dependency (Homebrew on macOS). Both paths produce the same virtual environment and work the same way once activated.

Editing Python Programs in the Terminal#

With Python installed and a virtual environment active, you need a way to create and edit .py files. This book is terminal-centric, so we recommend learning a terminal-based editor: Vim or Emacs. Both run inside the terminal, are available on every Unix-like system, and are widely used by professional programmers. VS Code is an acceptable alternative if you prefer a graphical editor, but knowing at least one terminal editor is a valuable skill — especially when working on remote servers where graphical tools are unavailable.

Vim#

Vim is installed by default on macOS and most Linux distributions. To check:

vim --version

Opening a file

vim hello.py

If hello.py does not exist, Vim creates it when you save.

The two modes you need to know

Vim is a modal editor. When it opens, you are in Normal mode — keystrokes are commands, not text. To type, you switch to Insert mode:

  • Press i to enter Insert mode. The bottom of the screen shows -- INSERT --.

  • Type your program.

  • Press Esc to return to Normal mode.

Saving and quitting (from Normal mode):

  • :w — save (write) the file.

  • :q — quit.

  • :wq — save and quit in one step.

  • :q! — quit without saving (discard changes).

A complete example

vim hello.py

Press i, type:

print("Hello, world!")

Press Esc, then type :wq and press Enter. Run the program:

python hello.py

Output:

Hello, world!

Emacs#

Emacs is available on macOS via Homebrew and on Linux via the system package manager:

brew install emacs        # macOS
sudo apt install emacs    # Ubuntu / Debian

Opening a file

emacs hello.py

Key bindings

Emacs uses the Ctrl key (written C-) and the Meta key — usually Alt on Linux or Option on macOS (written M-):

  • Type normally — unlike Vim, Emacs starts in editing mode. Just start typing.

  • C-x C-s — save the file (hold Ctrl, press x, then hold Ctrl, press s).

  • C-x C-c — quit Emacs.

  • C-g — cancel any partially typed command.

A complete example

emacs hello.py

Type:

print("Hello, world!")

Press C-x C-s to save, then C-x C-c to quit. Run the program:

python hello.py

Output:

Hello, world!

VS Code (graphical alternative)#

If you prefer a graphical editor, Visual Studio Code works well with Python. Install the Python extension from Microsoft, then open a file or folder from the terminal:

code hello.py

VS Code integrates with virtual environments and supports running and debugging Python programs directly. It is a reasonable choice, but you will still need to use the terminal for running programs, managing packages, and working on remote systems — so the terminal skills in this chapter remain essential.