python

What this skill does

# Python Development Skill

Comprehensive guide to modern Python development covering conventions, testing, tooling, security, performance, and ecosystem best practices (2024-2025 standards).

## Tier 2 Quick Start

**For multi-file projects, team collaboration, and maintained code:**

```bash
# Install Python 3.12 and uv (see Installation guides)
# Windows: winget install Python.Python.3.12 && winget install astral-sh.uv
# macOS: brew install [email protected] uv
# Linux: apt install python3.13 && curl -LsSf https://astral.sh/uv/install.sh | sh

# Create new project with modern structure
uv init my-project
cd my-project

# Add dependencies
uv add requests httpx pydantic

# Add development dependencies
uv add --dev pytest pytest-cov ruff mypy

# Set up code quality (create pyproject.toml config - see assets/pyproject-toml-template.toml)
# Configure Ruff, mypy, pytest

# Write tests (pytest)
# tests/test_example.py - mirror src/ structure

# Run quality checks
uv run ruff check .          # Linting
uv run ruff format .         # Formatting
uv run mypy .                # Type checking
uv run pytest                # Run tests
uv run pytest --cov          # With coverage
```

## When to Use This Skill

Invoke this skill when you need guidance on:

- **Installation & Setup**: Installing Python 3.12/3.14, uv, setting up development environment
- **Code Style**: Following PEP-8, configuring Ruff/Black, naming conventions
- **Project Structure**: Organizing code with src/ layout, imports, package structure
- **Dependency Management**: Using uv, Poetry, pip, virtual environments, pyproject.toml
- **Testing**: Writing pytest tests, fixtures, parametrization, coverage, mocking
- **Type Hints**: Modern typing patterns, mypy configuration, protocols, generics
- **Code Quality**: Setting up Ruff, mypy, Bandit, pre-commit hooks, CI/CD
- **Async Programming**: asyncio patterns, async/await, TaskGroup, structured concurrency
- **Security**: OWASP best practices, input validation, dependency scanning
- **Performance**: Profiling, optimization patterns, Cython
- **Packaging**: pyproject.toml, PyPI publishing, versioning, distribution
- **Common Libraries**: Standard library essentials, ecosystem overview
- **Documentation**: Docstrings (PEP-257), Sphinx, documentation generation

## Overview

This skill provides modern Python development guidance aligned with current best practices (2024-2025):

**Core Standards:**

- **Style**: PEP-8 (enforced via Ruff)
- **Type Hints**: PEP-484, PEP-526, modern syntax (PEP-604: `str | None`)
- **Packaging**: PEP-517, PEP-518 (pyproject.toml)
- **Docstrings**: PEP-257
- **Testing**: pytest (industry standard)
- **Dependency Management**: uv (fastest) or Poetry (feature-rich)

**Modern Tooling (2024-2025):**

- **Linter/Formatter**: Ruff (replaces flake8, isort, optionally Black)
- **Type Checker**: mypy with strict mode
- **Test Framework**: pytest
- **Dependency Manager**: uv or Poetry
- **Security Scanner**: Bandit + pip-audit
- **Project Config**: pyproject.toml (universal)

**Project Structure:**

- src/ layout (modern standard, not flat layout)
- Absolute imports preferred over relative
- Tests mirror src/ structure
- pyproject.toml for all configuration

**Official Sources:**
All guidance backed by official Python documentation, PEPs, and tool documentation:

- docs.python.org
- peps.python.org
- docs.astral.sh/ruff
- docs.astral.sh/uv
- mypy-lang.org
- docs.pytest.org

## Quick Tier Selection

**Choose your complexity level:**

### 🎯 Tier 1: Minimal (Simple Scripts)

→ Single-file utilities, converting scripts, one-off automation
→ Just Python code - no tooling overhead
→ [Jump to Minimal Guidance](#tier-1-minimal-simple-scripts)

### 📦 Tier 2: Standard (Organized Projects)

→ Multi-file modules, team projects, maintained code
→ Modern project structure + testing
→ [Jump to Standard Guidance](#tier-2-standard-organized-projects)

### 🚀 Tier 3: Full (Production Systems)

→ PyPI packages, enterprise systems, production deployments
→ Complete tooling ecosystem
→ [Jump to Full Guidance](#tier-3-full-production-systems)

**Not sure?** Default to Tier 2 (Standard) - it covers most use cases.

---

## Tier 1: Minimal (Simple Scripts)

**For:** Single-file utilities, script conversions, and simple automation.

### Setup

Just Python 3.12+ - no additional tooling required:

- ✅ No uv, no virtual environment needed
- ✅ No pyproject.toml, no src/ layout
- ✅ Optional: Install Ruff for quick linting (`pip install ruff`)

### Code Standards

Follow these simple principles:

- **PEP-8 naming**: `snake_case` for functions/variables, `PascalCase` for classes
- **Type hints**: Add for clarity (helps readers understand your code)
- **Docstrings**: Simple descriptions of what functions do
- **pathlib**: Use `pathlib.Path` for file operations (not `os.path`)
- **Built-ins**: Use Python's built-in `json`, `datetime`, `sys` modules

### Example: Simple Logging Script

```python
#!/usr/bin/env python3
"""Simple logging utility - converts event to JSON."""

import json
import sys
from datetime import datetime, timezone
from pathlib import Path


def log_event(event_name: str, data: dict) -> None:
    """
    Log an event to daily JSONL file.

    Args:
        event_name: Name of the event
        data: Event data to log
    """
    log_dir = Path(__file__).parent / "logs"
    log_dir.mkdir(exist_ok=True)

    now = datetime.now(timezone.utc)
    log_file = log_dir / f"{now:%Y-%m-%d}.jsonl"

    entry = {
        "timestamp": now.isoformat(),
        "event": event_name,
        "data": data
    }

    with open(log_file, "a", encoding="utf-8") as f:
        f.write(json.dumps(entry) + "\n")


if __name__ == "__main__":
    if len(sys.argv) < 2:
        print("Usage: script.py <event_name>", file=sys.stderr)
        sys.exit(1)
    event_name = sys.argv[1]
    data = json.loads(sys.stdin.read())
    log_event(event_name, data)
```

### Optional: Quick Linting

If you want to check your code style:

```bash
# Install Ruff (optional)
pip install ruff

# Check code
ruff check script.py

# Format code
ruff format script.py
```

### When to Upgrade to Tier 2

Consider upgrading to Tier 2 (Standard) when:

- ✅ Script grows to 3+ files
- ✅ Multiple people working on code
- ✅ Need automated testing
- ✅ Managing external dependencies
- ✅ Code will be maintained long-term

---

## Tier 2: Standard (Organized Projects)

**For:** Multi-file modules, team projects, and maintained code.

Modern Python project setup with proper structure, testing, and quality tools.

### Installation

Install Python 3.12+ and uv (modern dependency manager). See platform-specific guides:

- [Installation Overview](references/installation/overview.md) - Concepts and version policy
- [Windows Installation](references/installation/windows.md) - WinGet, Python Launcher
- [macOS Installation](references/installation/macos.md) - Homebrew installation
- [Linux Installation](references/installation/linux.md) - apt/dnf or build from source

### Project Setup and Organization

**Conventions and Style** - Follow PEP-8 with Ruff for linting and formatting:

- See [Conventions and Style Guide](references/conventions-and-style.md)

**Project Structure** - Use modern src/ layout for proper packaging:

- See [Project Structure Guide](references/project-structure.md)

**Dependency Management** - Choose between uv (fastest), Poetry (feature-rich), or pip+venv:

- See [Dependency Management Guide](references/dependency-management.md)

### Testing and Quality

**Testing** - Use pytest with fixtures, parametrization, and coverage:

- See [Testing Methodology Guide](references/testing-methodology.md)

**Type Hints** - Modern typing with mypy, protocols, and generics:

- See [Type Hints Guide](references/type-hints.md)

**Code Quality** - Set up Ruff, mypy, Bandit, and pre-commit hooks:

- See [Code Quality Tools Guide](references/code-quality-tools.md)

### Advanced Development

**Async Programming** - asy