Python is the most popular first programming language in the world right now — for good reasons: clean syntax, batteries-included standard library, huge ecosystem, and you can be productive in an afternoon. This post is the first step of a step-by-step course written like a university lecture series. Each post adds one well-scoped layer; by Post 05 you'll be comfortable with files, exceptions, and modules. Future posts extend into stdlib, async, typing, and beyond.

Series map: 00 Setup (this post) → 01 Syntax → 02 Data Structures → 03 Functions & Modules → 04 OOP → 05 Files & Exceptions → (future) stdlib · async · typing · packaging.

Learning Outcome

Install Python 3 on Windows / macOS / Linux.
Run the REPL (interactive interpreter) and a script file.
Understand the difference between interpreter, script, and REPL.
Write and run "Hello, World" + an interactive greeting program.
Set up a basic project folder + venv (virtual environment).

Chapter 1 — What Python is (and isn't)

Terminology

Interpreter — the program (python or python3) that reads and executes Python code line by line.
REPL — Read-Eval-Print Loop: an interactive shell where each line you type is executed immediately.
Script — a .py file containing Python code, run with python script.py.
Module — a .py file imported by another file.
Package — a directory of modules with an __init__.py.
PEP — Python Enhancement Proposal. The language's design documents. PEP 8 is the style guide everyone follows.

Python vs other languages (one paragraph)

Python is interpreted (no compile step), dynamically typed (you don't declare types, though you can hint them), and garbage-collected (no manual memory management). The trade-off vs C++/Rust: Python is 10–100× slower in raw computation but 5–10× faster to write. For data work, web back-ends, scripts, automation, and ML, the slowness almost never matters.

Trick: don't compare languages by speed in isolation. Compare by time-to-correct-program. Python wins almost every "write something useful by Friday" race.

Chapter 2 — Installation

Windows

Visit python.org/downloads.
Download the latest Python 3.12+ installer.
Critical: tick "Add Python to PATH" on the first installer screen.
Click "Install Now".
Open a new Command Prompt or PowerShell. Run:

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2 python --version

Should print Python 3.12.x. If "command not found", you missed step 3 — reinstall.

macOS

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5 # Option 1: official installer from python.org
# Option 2: Homebrew (recommended)
brew install python@3.12
python3 --version

Trick: macOS ships with an old python that points to Python 2 or a system Python. Always use python3 (and pip3) on macOS unless you've set up aliases.

Linux (Debian/Ubuntu)

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4 sudo apt update
sudo apt install -y python3 python3-pip python3-venv
python3 --version

Fedora / Arch: similar — use your package manager.

Chapter 3 — The REPL

Open a terminal and type python (or python3 on macOS/Linux):

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Python 3.12.4 (main, ...) on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 1 + 1
2
>>> name = "Ada"
>>> f"Hello, {name}"
'Hello, Ada'
>>> exit()

The >>> prompt waits for input; each expression's result is printed automatically. Indented blocks use ... as the continuation prompt:

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...     print(i)
...
0
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The REPL is your calculator + sandbox. Use it to test snippets, explore stdlib, check syntax.

Trick: the underscore _ in the REPL holds the last result. 2 + 2 then _ * 10 gives 40. Useful for chained quick math.

Chapter 4 — Your first script

Create a file hello.py:

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3 # hello.py
print("Hello, World!")

Run it:

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2 python hello.py

Output: Hello, World!

Interactive version

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4 # greet.py
name = input("What is your name? ")
print(f"Hi, {name}!")

Run, type your name, get greeted. Two concepts introduced:

input(prompt) reads a line of text from the user.
f"..." is an f-string: any {expression} inside is evaluated and substituted.

Shebang (Linux / macOS only)

Add #!/usr/bin/env python3 as the first line of a script, then chmod +x hello.py, and run with ./hello.py. The OS reads the shebang to know which interpreter to use.

Chapter 5 — Virtual environments (venv)

Each Python project should have its own isolated package list. This prevents "global pip install" chaos.

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17 # create a venv in a folder named .venv
python -m venv .venv
 
# activate it
# Windows (PowerShell):
.venv\Scripts\Activate.ps1
# Windows (cmd):
.venv\Scripts\activate.bat
# macOS / Linux:
source .venv/bin/activate
 
# install something
pip install requests
 
# deactivate when done
deactivate

After activation, your shell prompt usually shows (.venv) as a prefix. Any pip install only affects this venv, not the system Python.

Two projects, each with its own virtual environment and package versions, and the five venv commands

Where I got stuck: I skipped venvs for a year. Then one project needed requests==2.20 and another needed requests==2.28. Mass-upgrading broke the older project. The fix took an hour; the fix would have taken 0 hours with venvs. Always use a venv.

requirements.txt

Pin your dependencies:

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# later, on another machine:
pip install -r requirements.txt

Chapter 6 — Editor / IDE choice

Tool	Notes
VS Code + Python extension	Free, fast, huge ecosystem. Recommended for beginners.
PyCharm Community	Heavier, more "IDE feel", excellent refactoring.
Jupyter Notebook / Lab	Notebooks for data work. Use `pip install jupyterlab`.
Neovim / Vim + plugins	For terminal lovers. Slow to set up well.
IDLE	Ships with Python. Fine for first hour, then upgrade.

Pick one. Don't tool-shop for weeks — pick VS Code if undecided.

Practice Exercises

Exercise 1 — Hello, Self

Write intro.py that prints three lines:

Your name
Today's date (hard-code or use the datetime module — peek ahead!)
One thing you want to learn from this course

Exercise 2 — Temperature converter

Write temp.py that:

Asks the user for a temperature in Celsius.
Converts to Fahrenheit: F = C * 9/5 + 32.
Prints both.

Sample run:

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25.0°C = 77.0°F

Hint: input() returns a string; convert with float(...).

Solution

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f = c * 9 / 5 + 32
print(f"{c}°C = {f}°F")

Exercise 3 — Set up a project

Create folder python-course/.
cd into it.
Create a venv called .venv and activate it.
Install rich (pip install rich).
Run this script:

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3 from rich import print
print("[bold green]It works![/bold green]")

If you see green bold text, your venv setup is correct.

Cheat-sheet

What	How
Run REPL	`python` or `python3`
Run script	`python script.py`
Check version	`python --version`
Create venv	`python -m venv .venv`
Activate venv (Win)	`.venv\Scripts\Activate.ps1`
Activate venv (Unix)	`source .venv/bin/activate`
Install package	`pip install <name>`
Freeze deps	`pip freeze > requirements.txt`
Restore deps	`pip install -r requirements.txt`
Exit REPL	`exit()` or Ctrl+D (Unix) / Ctrl+Z + Enter (Win)

What's next

Post 01 covers Python's syntax basics: variables, types, operators, control flow (if, for, while), and the indentation rule that makes Python visually distinct.

References

docs.python.org — official docs (the only one you'll need long-term).
PEP 8 — style guide.
Real Python — well-written tutorials.
Fluent Python by Luciano Ramalho — the best "I know basics, now teach me deeply" book.