/python-dev

name: python-dev
description: Opinionated Python development setup with uv + ty + ruff + pytest + just. Use when creating new Python projects, setting up pyproject.toml, configuring linting, type checking, testing, or build tooling. Triggers on "python project", "uv init", "pyproject.toml", "ruff config", "ty check", "pytest setup", "justfile", "python linting", "python formatting", "type checking python".
metadata:
  version: "0.2.3"
  upstream: "uv@0.11.8, ty@0.0.33, ruff@0.15.12, ruff-pre-commit@0.15.12, pytest@9.0.3, pytest-asyncio@1.3.0, pre-commit@4.6.0, pre-commit-hooks@6.0.0"
  openclaw:
    homepage: https://github.com/tenequm/skills/tree/main/skills/python-dev
    emoji: "🐍"

Python Development Setup

Opinionated, production-ready Python development stack. No choices to make - just use this.

When to Use

• Starting a new Python project
• Modernizing an existing project (migrating from pip/poetry/mypy/black/flake8)
• Setting up linting, formatting, type checking, or testing
• Creating a Justfile for project commands
• Configuring pyproject.toml as the single source of truth

The Stack

| Tool | Role | Replaces | |------|------|----------| | [uv](https://docs.astral.sh/uv/) 0.11+ | Package manager, Python versions, runner | pip, poetry, pyenv, virtualenv | | [ty](https://docs.astral.sh/ty/) (beta) | Type checker (Astral, Rust) | mypy, pyright | | [ruff](https://docs.astral.sh/ruff/) | Linter + formatter | flake8, black, isort, pyupgrade | | [pytest](https://docs.pytest.org/) | Testing | unittest | | [just](https://just.systems/) | Command runner | make |

> **Note on ty**: ty is in beta (0.0.x). It's fast and improving rapidly, but still missing features and may produce false positives on heavy-typing libraries (Pydantic, Django, SQLAlchemy). For projects that need rock-solid type checking today, swap `ty` for `pyright` and keep the rest of the stack unchanged.

Quick Start: New Project

# 1. Create project with src layout
uv init --package my-project
cd my-project

# 2. Pin Python version
uv python pin 3.13

# 3. Add dev dependencies
uv add --dev ruff ty pytest pytest-asyncio pre-commit

# 4. Create Justfile (see template below)
# 5. Configure pyproject.toml (see template below)
# 6. Run checks
just check

pyproject.toml Template

This is the single config file. Copy this and adjust `[project]` fields.

[project]
name = "my-project"
version = "0.1.0"
description = "Project description"
readme = "README.md"
requires-python = ">=3.13"
license = {text = "MIT"}
dependencies = []

[project.scripts]
my-project = "my_project:main"   # CLI: `uv run my-project` -> main() in src/my_project/__init__.py

[dependency-groups]
dev = [
    "ruff>=0.15.0",
    "ty>=0.0.30",
    "pytest>=9.0.0",
    "pytest-asyncio>=1.3.0",
    "pre-commit>=4.0.0",
]

[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"

[tool.hatch.build.targets.wheel]
packages = ["src/my_project"]

# =============================================================================
# RUFF - Loose, helpful rules only
# =============================================================================
[tool.ruff]
target-version = "py313"
line-length = 100

[tool.ruff.lint]
select = [
    "E",   # pycodestyle errors - syntax issues
    "F",   # pyflakes - undefined vars, unused imports
    "I",   # isort - import sorting
    "UP",  # pyupgrade - modern Python syntax
]
ignore = [
    "E501",   # line too long - formatter handles it
    "E741",   # ambiguous variable name - sometimes makes sense
    "UP007",  # X | Y unions - Optional[X] is more readable
]
exclude = [".git", ".venv", "__pycache__", "build", "dist"]

[tool.ruff.format]
quote-style = "double"
indent-style = "space"
line-ending = "lf"

# =============================================================================
# TY - Type Checker
# =============================================================================
[tool.ty.environment]
python-version = "3.13"

[tool.ty.src]
include = ["src"]

# =============================================================================
# PYTEST
# =============================================================================
[tool.pytest.ini_options]
testpaths = ["tests"]
python_files = ["test_*.py"]
python_classes = ["Test*"]
python_functions = ["test_*"]
asyncio_mode = "auto"
addopts = [
    "--strict-markers",
    "--strict-config",
    "-ra",
]

Justfile Template

# Check types and lint
check:
    uv run ty check
    uv run ruff check --fix && uv run ruff format

# Run tests
test *ARGS:
    uv run pytest {{ARGS}}

# Run tests with coverage
test-cov:
    uv run pytest --cov=src --cov-report=term-missing

# Auto-fix and format
fix:
    uv run ruff check --fix
    uv run ruff format

# Install/sync all dependencies
install:
    uv sync --all-groups

# Update all dependencies
update:
    uv lock --upgrade
    uv sync --all-groups

# Clean build artifacts
clean:
    rm -rf dist/ build/ .pytest_cache/ .ruff_cache/ htmlcov/
    find . -type d -name __pycache__ -exec rm -rf {} + 2>/dev/null || true

Pre-commit Config

Create `.pre-commit-config.yaml`:

repos:
  - repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v6.0.0
    hooks:
      - id: check-added-large-files
        args: ['--maxkb=1000']
        exclude: ^uv\.lock$
      - id: detect-private-key
      - id: check-merge-conflict
      - id: check-yaml
      - id: check-toml
      - id: end-of-file-fixer
      - id: trailing-whitespace
      - id: mixed-line-ending
        args: ['--fix=lf']

  - repo: https://github.com/astral-sh/ruff-pre-commit
    rev: v0.15.12
    hooks:
      - id: ruff
        args: [--fix]
      - id: ruff-format

exclude: |
  (?x)^(
    \.venv/.*|
    \.git/.*|
    __pycache__/.*|
    build/.*|
    dist/.*|
    uv\.lock
  )$

Then run: `uv run pre-commit install`

Project Structure

Always use src layout:

my-project/
  src/
    my_project/
      __init__