Python Modern Coding Guide

Problem

Python projects often mix older syntax with inaccurate version assumptions. When an agent writes code without a clear target version, it may introduce match/case, type statements, or asyncio.TaskGroup that fail on older runtimes. It may also over-defer to legacy patterns, missing list[int], @dataclass, and tomllib.

How it works

The skill first identifies the target version from pyproject.toml, setup.cfg, Pipfile, setup.py, or .python-version, then generates code within that version ceiling. Core rules include top-level imports except for optional dependencies or circular-import workarounds, mandatory type annotations on functions and module/class variables, avoidance of from __future__ import annotations, quoted forward references, and sphinx-notypes docstrings. It prefers modern stdlib features by version, such as list[int], dict | dict, and zoneinfo for 3.9+, and ExceptionGroup, tomllib, and asyncio.TaskGroup for 3.11+.

Boundaries

This is a coding-style constraint, not a replacement for ruff, mypy, pytest, or a CI version matrix. If repository version metadata is missing, the target version must be chosen explicitly. Avoid using newer syntax in older projects, and be careful when adjusting annotation strategies for runtime-annotation-sensitive libraries.