Python Project

Frameworks & Libraries

• CLI: use Typer — always fetch latest docs
• Web API: use FastAPI — always fetch latest docs
• Dependencies: pyproject.toml + uv. Pin the tool version with required-version in [tool.uv], exclude fresh deps with exclude-newer = "30 days", and declare the package index explicitly with [[tool.uv.index]] (explicit = true). For production Docker images, export locked deps with uv export --no-dev --no-emit-project -o requirements.txt and install with pip install --require-hashes.
• Build: hatchling; use hatch when needed
• Structure: packages over monolithic files; no module > 500 lines; no name-prefix modules

Testing & Coverage

• 100% coverage required; no # pragma: no cover or # type: ignore — fix the root cause instead (cast, explicit annotation, restructure). The only exception is inherently untypeable code (e.g. SQLAlchemy dynamic attribute access), and even then prefer cast() or a typed helper.
• Tests for all new features, bug fixes, critical paths, and edge cases (empty inputs, invalid types, large datasets)

Code Standards

• PEP 8; 4-space indent; 79-char line limit; English only regardless of prompt language
• Type hints on all functions; typing module for annotations
• PEP 257 docstrings on public API only — private functions (_name) only if logic is non-obvious
• No docstrings on tests — test function names must be descriptive enough to stand alone
• No inline comments for self-explanatory code — names and types are the documentation; comment why, not what
• Descriptive names; break complex functions into smaller ones
• Handle edge cases explicitly; document design decisions in comments

Project scaffolding

When creating a new Python project, write a .gitignore to the project root:

# Python
__pycache__/
*.pyc
*.pyo

# Virtual environment
.venv/

# Tools
.mypy_cache/
.pytest_cache/
.ruff_cache/

# Coverage
.coverage
coverage/
coverage.xml
htmlcov/

# Build
dist/
build/
*.egg-info/

# Environment
.env

Documentation example

def calculate_area(radius: float) -> float:
    """Return the area of a circle with the given radius."""
    import math
    return math.pi * radius ** 2