Overview

Prerequisites

• Prior topics: 1 · Just Enough Nvim -- you should be comfortable opening, editing, and saving files before writing and running Python scripts; the Pass 0 forge capstone is recommended but not required.
• Tools & environment: a macOS/Linux terminal; Python 3.x installed (python3 --version) with venv and pip (both ship with CPython); the black, ruff, and pyright CLIs, installable via pip. Python is licensed under the PSF License Version 2, a Tier-1 free-to-teach license.
• Assumed knowledge: basic terminal use. No prior Python is required -- this is the reader's Python starting point.

Why this exists -- the big idea

Pass 1-3 build real software, and they need one default language you can read and run without ceremony -- this primer makes Python that tool before the topics that lean on it. The one idea worth keeping if you forget everything else: Python is executable pseudocode -- optimize for the reader first; clarity is the whole point, and speed is bought back later only where measured.

Cross-cutting big ideas: abstraction-and-its-cost -- Python's high-level built-ins (lists, dicts, comprehensions) buy readable code and charge runtime overhead you spend deliberately, not by default; every comprehension in this primer is exactly that trade made visible. correctness-vs-pragmatism -- Python's type hints are optional and unenforced at runtime (Example 84 proves it directly): the language lets you ship first and verify later with a separate tool (pyright), rather than forcing "provably right" before anything runs at all. Both ideas recur throughout this primer's worked examples, not just in this opening section.

Install and run your first script

Install Python 3 for your platform (macOS: brew install python@3.14; Debian/Ubuntu: your distribution's current python3 package, or download from python.org/downloads), then confirm the version:

$ python3 --version
Python 3.14.3

A note on versions: this primer's examples were authored and verified against CPython 3.14.3, the version installed in the sandbox that produced every captured "Output" block on this site. python.org lists 3.14.6 (2026-06-10) as the current published patch release at authoring time -- any 3.14.x patch behaves identically for everything this primer teaches (f-strings, type hints, comprehensions, match, and the standard library surface used here are all stable across 3.14 patch releases). black 26.5.1 and ruff 0.15.21 are the exact versions this primer's black/ruff examples (4, 5, 68, 81) were run against; pyright 1.1.411 is the exact version Examples 83-84 were run against. All three are CVE-clean at authoring time. Strict mode for pyright is set via config ("typeCheckingMode": "strict") or an inline # pyright: strict comment -- there is no --strict CLI flag.

Every example in this primer is a complete, self-contained .py file (or small file set) colocated under learning/code/. The command you will run for almost every one of them is exactly this:

python3 example.py

Exceptions, all deliberate: Examples 2-5 demonstrate CLI workflows (-c inline execution, venv creation, black, ruff) rather than a single script run; Examples 46, 47, 61-64, 73-75, 81-82 name their file differently (mod.py, cli.py, a package under app/, and so on) because the filename itself is part of what the example teaches -- each one states its exact run command in its own Run line.

How this primer is organized

• Beginner (Examples 1-28) -- running Python three ways, virtual environments, black/ruff, the primitive types and type hints, operators, f-strings and string methods, lists, tuples, dictionaries, sets, slicing, conditionals, and loops.
• Intermediate (Examples 29-60) -- comprehensions and generator expressions, functions (typed signatures, defaults, keyword args, *args/**kwargs, multiple returns), lambdas and closures, scope, modules and imports, exceptions, file I/O, JSON, and a first pass at classes.
• Advanced (Examples 61-84) -- argparse CLIs, multi-module packages, custom exception classes and exception chaining, dataclasses, ruff-clean typed signatures, generator functions, custom context managers, JSON pipelines, pytest unit tests, and static type checking with pyright (including the one case where pyright catches a bug that python3 itself does not).

Every example cites the concept (co-NN) it exercises, and every claim about Python's version, license, and tooling traces to python.org, docs.python.org, peps.python.org, PyPI, and docs.pytest.org, web-verified 2026-07-12/13 and re-confirmed 2026-07-14.

Scope: just enough, not comprehensive

This is a Primer, not a comprehensive Python reference: it covers exactly the language surface Pass 1-3's Python-primary topics depend on, and deliberately excludes decorators beyond @dataclass, async/await, metaclasses, descriptors, the full typing module (Protocol, Generic, overload), packaging/distribution (pyproject.toml, wheels, publishing), threading/multiprocessing, and C-extension interop. Full object-oriented Python is previewed here (Examples 59, 60, 65, 67, 71) and gets its complete treatment in a later topic. If a Python feature is not exercised by a later topic in this journey, it is out of scope here on purpose, not by oversight.

← Previous: Pass 0 Capstone · Forge-Ready · Next: Beginner Examples →