Python Guide

Applies to: Python 3.11+, APIs, CLIs, Data Pipelines, Automation

Core Principles

1. Type Hints Everywhere: All function signatures, class attributes, and module-level variables must have type annotations
2. Explicit Over Implicit: No * imports, no mutable default arguments, no implicit type coercions
3. Virtual Environments Always: Never install into system Python; use venv, uv, or poetry
4. Pytest Over unittest: Use pytest for all testing; fixtures and parametrize over setUp/tearDown
5. PEP 8 + Ruff: Enforce style mechanically; never rely on manual formatting

Guardrails

Python Version

• Target Python 3.11+ (use match statements, ExceptionGroup, tomllib)
• Set requires-python = ">=3.11" in pyproject.toml
• Use from __future__ import annotations for forward references in 3.11