# Class Design

> Python class design conventions for this codebase. Apply when writing or reviewing classes including interfaces, inheritance, composition, and attribute access. Use when this capability is needed.

- Skill: `tomevault-io/class-design` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/class-design`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/class-design/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/class-design

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# Class Design Conventions

Favor composition over inheritance. Use Protocol classes for interfaces and dependency injection for shared behavior.

**Layers**:
- `rules.md` - Quick reference and decision flow
- `examples.md` - Detailed code examples

## Quick Reference

| Principle | Pattern |
|-----------|---------|
| Interfaces | `Protocol` classes for duck typing |
| Shared behavior | Dependency injection or mixins |
| Inheritance depth | Maximum 2 levels |
| Framework base classes | OK to inherit (`BaseModel`, `nn.Module`) |
| Concrete inheritance | Forbidden—use mixins instead |
| Static methods | Avoid—use module-level functions |
| Internal APIs | Design for extension, not restriction |
| Private attributes | Only to avoid subclass naming conflicts |
| Getters/setters | Use plain attributes instead |

For rules: see `rules.md`
For examples: see `examples.md`

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<!-- tomevault:4.0:skill_md:2026-04-14 -->