Chapter 2, Environment

Installing Python on macOS, Windows, and Linux

The correct way to install varies by operating system, and the wrong way often costs hours later. I show the path I use for each one.

Code for this chapter: ambiente/cap02_instalacao.py

Which version to install

Install the latest stable series, which when I wrote was 3.14, and never download anything below 3.12 for a new project. Python 3.10 goes out of support in October 2026.

A rule that saves me headaches: the Python that came with the system is for the system. It serves macOS or your Linux distribution, which depend on a specific version. For your projects, install a separate Python.

Install by operating system

The most straightforward way is Homebrew. If you don't have it yet, install it from the official site (brew.sh) and then:

Terminal

brew install python
python3 --version

You can also download the installer from the official site (python.org, macOS section), which works on Intel and Apple Silicon Macs. I prefer Homebrew because updating becomes a command.

On macOS, the command is python3. The command python alone only exists within a virtual environment or when you use pyenv or uv.

Error externally-managed-environment
On recent Linux distributions and in Homebrew, running pip install outside of a virtual environment fails with the message externally-managed-environment. This is intentional (the rule is called PEP 668) and protects the system Python. The correct solution is to create a virtual environment, which is the subject of chapter 4. Do not use --break-system-packages.

Check the installation

Before anything else, confirm the version in the terminal. Use python3 --version on macOS and Linux, and py --version on Windows. Then, run this script, which shows where your Python comes from:

ambiente/cap02_instalacao.pylinhas 10 a 16

import platform
import sys

print("Versão:", platform.python_version())
print("Implementação:", platform.python_implementation())
print("Executável:", sys.executable)
print("Sistema:", platform.system())

Output

Versão: 3.14.6
Implementação: CPython
Executável: /opt/homebrew/bin/python3
Sistema: Darwin

The block above is an example from a Mac with Homebrew. Your output will vary, and that's exactly what you want to observe: the path of the executable tells you which Python you are actually using.

The commands python, python3, and py

Situation	Command
macOS and Linux, outside of a venv	`python3`
Windows, outside of a venv	`py`
Inside a virtual environment (any system)	`python`
With pyenv or uv configured	`python`

The interactive mode (REPL)

Type python3 (or py) without arguments to open interactive mode, great for testing a quick expression:

Console Python

>>> 2 + 2
4
>>> "python".upper()
'PYTHON'
>>> exit()