Modern Python

First-party. MIT. Id: modern-python. SKILL.md only. No scripts/. Not a vendor paste. Tool facts from the public uv, ruff, ty, and pytest docs.

Load-with list and lang-python pointer: language-router Load-with list, Map.

Iron law

uv add / uv remove change dependencies. uv run runs tools. Do not activate a venv or hand-edit dependency lists.

On new work, use Python 3.12+, uv, ruff (lint and format), ty, pytest. Keep pip / Poetry / mypy / black only when the operator says so.

Always

Ask first

Never

Decision

Tools

Scanners and CI hooks are tester / security, not this skill.

New project

uv init myproject
cd myproject
uv add httpx
uv add --dev pytest ruff ty
uv sync
uv run pytest
uv run ruff check .
uv run ruff format --check
uv run ty check .

Package:

uv init --package myproject
cd myproject
uv sync
uv build

uv add owns [project].dependencies and the dev group. Never type packages into pyproject.toml by hand; run uv add.

PEP 723 scripts

#!/usr/bin/env -S uv run --script
# /// script
# requires-python = ">=3.12"
# dependencies = [
#     "httpx",
# ]
# ///

import httpx

print(httpx.get("https://example.com").status_code)

uv init --script myscript.py
uv add --script myscript.py httpx
uv run myscript.py

No lockfile. If the code spans more than one file, use pyproject.toml. Use uv run --with pkg only as a one-off probe; add project deps with uv add.

Migration

Migrate only when asked.

If a requirement has odd markers or is a VCS dep, stop and do it by hand. Never import a lock you have not read; read it first.

uv (short)

Verify

uv run pytest
uv run ruff check .
uv run ruff format --check
uv run ty check .

Roles

Red flags

• “I’ll pip install just this once”
• “source the venv”
• “hand-edit pyproject to add the package”
• “keep requirements.txt and uv”
• “copy a vendor Python skill pack”

Stop. Use uv. Or Ask first.

License

MIT. First-party. See repo LICENSE and SOURCES.md.