Python Coding Conventions

Coding standards for Python projects at Tenzir.

Required Tools

All projects use:

• uv — Dependency management and virtual environments
• Ruff — Linting and formatting
• Mypy — Static type checking
• pytest — Testing

Default Libraries

Prefer to use these libraries to ensure uniform codebase across Tenzir repositories:

• pydantic - Defining and validating models
• FastAPI - Declaring REST APIs
• Click - Providing a CLI interface

Quality Gates

Run before committing or releasing:

uv run ruff check \
  && uv run ruff format --check \
  && uv run mypy \
  && uv run pytest \
  && uv build

The chain fails fast on the first error.

Python Version

Target Python 3.12+. Use modern syntax and stdlib features freely—no backwards-compatibility with older versions.

Coding Style

Formatting

• Ruff controls whitespace: 4-space indentation, double-quoted strings
• 88 character line limit (Ruff/Black default)
• Let Ruff order imports automatically

Type Hints

• All public surfaces must be fully typed
• Strict Mypy settings reject untyped or partial definitions
• Avoid Any; fix warnings rather than ignoring them

Package structure and imports

• Keep __init__.py files empty. They are only used to mark a directory as importable but do not contain any content, let alone non-trivial code.
• Always use absolute imports from the package top level: from this_package.foo import bar instead of from .foo import bar.
• Never use wildcard imports

Naming Conventions

Element	Convention	Example
Modules	snake_case	my_module.py
Functions	snake_case	calculate_total()
Variables	snake_case	user_count
Classes	PascalCase	DataProcessor
Constants	CONSTANT_CASE	MAX_RETRIES

CLI Conventions

• Use kebab-case for CLI flags: --output-file, not --output_file
• Keep user messages concise

Documentation Style

• Write in active voice; rewrite passive sentences before committing
• Focus on user-facing impact, not implementation details
• Use explicit imports; isolate configuration helpers in config.py

Unit Test Conventions

• Use pytest as testing framework
• Use CliRunner for end-to-end CLI testing
• Favor tmp_path for filesystem tests
• Use parametrization for scenario variation
• Maintain ≥80% coverage when coverage is configured

Project Setup

Only read the specific file you need when setting up a new project or modifying that tool's configuration:

• project-structure.md — Directory layout and testing conventions
• pyproject.md — Project metadata and build config
• ruff.md — Ruff linting and formatting config
• mypy.md — Mypy type checking config
• pytest.md — Pytest runner config
• coverage.md — Coverage reporting config
• dev-dependencies.md — Dev dependency group
• upgrading-dependencies.md — Upgrading and committing dependency changes