How to read the examples

Project overview and reading path

Each recommendation follows one situation: typical Python, a better alternative, and what changes for the caller. Short sketches omit imports and unrelated setup. Each Source link opens the complete checked example within the book; you do not need Python, a terminal, or a repository clone.

A line such as # rejected[missing-attribute]: workers = outcome.workers means the checker rejects the statement after the colon. Here the model declares workers, but the outcome might be InvalidMetadata. The diagnostic category is shown so the result is visible without running anything. These comments are not suppressions.

The examples use Python 3.11+, Pyrefly 1.3.1, and Ruff 0.16.9. Pydantic validates external inputs; pytest checks behavior. These are the book’s reference tools, not reader prerequisites. Contributor checks verify source links, runtime behavior, and the intended diagnostic for each rejected statement.