Installation & Setup

Introduction

Before you can write a single line of Python, you need Python itself installed on your computer. Unlike languages that run in a browser, Python code needs an interpreter installed locally to read and execute it.

This lesson walks through downloading and installing Python on Windows, macOS, and Linux, confirming the install worked, and picking an editor so you are fully ready to write real code.

Downloading Python

The official source for Python is python.org. Visiting the Downloads page automatically detects your operating system and offers the latest stable release, which is the version recommended for almost everyone starting out.

Always download Python from python.org (or your operating system's trusted package manager) rather than an unofficial source, to avoid modified or unsafe installers.

Installing on Windows

On Windows, download the installer .exe from python.org and run it. The single most important step is on the very first installer screen: make sure the checkbox labeled "Add python.exe to PATH" (or "Add Python to PATH") is checked before clicking Install Now.

Adding Python to PATH lets you type python from any folder in the terminal (Command Prompt or PowerShell) without typing the full install location. Skipping this checkbox is the most common reason beginners get a "python is not recognized" error afterward.

Installing on macOS

On macOS, download the .pkg installer from python.org and run it like any other Mac application installer, following the on-screen steps. macOS ships with its own older system Python used internally by the operating system, so the python.org installer keeps your version separate and up to date.

After installing, macOS users typically run the command python3 rather than python, since the name python may be reserved by the system's built-in version.

Installing on Linux

Most Linux distributions already include Python 3 pre-installed. You can check your version and, if needed, install or update Python using your distribution's package manager.

# Debian/Ubuntu
sudo apt update
sudo apt install python3

# Fedora
sudo dnf install python3

As on macOS, Linux users typically use the command python3 to run the correct version.

Verifying Your Installation

Once installed, open a terminal (Command Prompt, PowerShell, or Terminal app) and check the installed version to confirm everything worked.

python --version
# or, on macOS/Linux
python3 --version

Python 3.12.4

If you see a version number like this, Python is installed correctly. If instead you see an error like "command not found" or "not recognized," Python is either not installed or not added to PATH.

What Is the REPL?

Typing python (or python3) alone with no filename opens the interactive interpreter, often called the REPL — short for Read, Evaluate, Print, Loop. It reads one line of code you type, evaluates it immediately, prints the result, and loops back for your next line.

The REPL is identified by the >>> prompt and is extremely useful for quickly testing small pieces of code without creating a file.

Example: Using the REPL

Open a terminal, type python (or python3), press Enter, and you will see the >>> prompt. Try typing a simple expression.

>>> 2 + 2
4
>>> print("Hello from the REPL")
Hello from the REPL
>>> exit()

Typing exit() (or pressing Ctrl+Z then Enter on Windows, or Ctrl+D on macOS/Linux) leaves the REPL and returns you to your normal terminal.

Choosing an Editor

The REPL is great for quick tests, but real programs are written and saved in .py files using a code editor. Beginners have several good, free options.

For this course, VS Code with the Python extension is the recommended setup — it is free, widely used in the industry, and works well for beginners and professionals alike.

Running a .py File

Once you save code in a file ending in .py, you run it from a terminal by typing python (or python3) followed by the filename, from the same folder the file is saved in.

python hello.py
# or, on macOS/Linux
python3 hello.py

Example: Running a Script

Create a file named hello.py containing a single line, save it, then run it from the terminal in that folder.

print("Setup complete!")

python hello.py

Setup complete!

Common Mistakes

Best Practices

Frequently Asked Questions

Key Takeaways

Summary

With Python installed and verified, and an editor ready to go, you now have everything you need to start writing real Python programs. The REPL is useful for quick experiments, while .py files and an editor are how you will build actual programs.

In this lesson, you installed Python, verified it works, explored the REPL, and learned how to run a .py file from the terminal. Next, you will write and run your very first complete Python program.