Setting Up Without the Ceremony
The usual first step in a Python tutorial is an hour of installer screenshots. Run one line without installing anything, and see the same interpreter everyone else is using.
The usual first step in a Python tutorial is an hour of installer screenshots. Most of that hour is unnecessary — check what is already on your machine before you install anything.
The one thing you actually need
You need exactly one thing to start: a working Python interpreter you can reach from a terminal. You do not need an editor with plugins, a virtual environment, or a project folder yet — those matter later, once you have more than a few lines to organise.
Most Mac and Linux machines ship with Python already installed. Pick what you are sitting at.
$ python3 --version# Python 3.12.x $ python3If that version line printed, you are done — skip ahead. If it said “command not found”, install Python 3 from python.org and run it again.
A terminal that already has it
Typing python3 (or py on Windows) with nothing after it drops you into the interactive interpreter, usually called the REPL — read, evaluate, print, loop. Type an expression, press return, and it is evaluated immediately.
$ >>> 2 + 2$ 4$ >>> "hello".upper()$ 'HELLO'Everything after the >>> was typed by you. Everything on the line below it is Python printing the result back, unprompted — the REPL shows you the value of every expression you enter, which is why it is the fastest way to check a small idea.
Where a file stops and a script begins
The REPL is for trying something out. A .py file is for keeping it. Save a few lines in a file named hello.py, and run the file itself rather than typing its contents by hand:
print("Hello, world!")$ python3 hello.py$ Hello, world!Nothing you type into the REPL is saved anywhere once you close it. Every program in the rest of this track assumes you are working in a file, not the REPL, for exactly that reason.
Key takeaways
- You need one thing to start: a Python interpreter reachable from a terminal.
- The REPL (python3 with nothing after it) evaluates expressions immediately and shows you the result.
- Nothing typed into the REPL is saved — real programs live in .py files.
- Run a file with python3 <filename>.py, not by retyping its contents into the REPL.