Python Feature Development

Overview

Layer-by-layer TDD workflow for FastAPI backends following clean architecture. Build inside-out: domain → application → infrastructure → interfaces. All code fully typed with mypy strict.

Core principle: Every layer gets its own test before implementation. Type safety is non-negotiable.

Layer-by-Layer Workflow

1. Domain Entity + Validation

# src/domain/user.py
from dataclasses import dataclass, field
from datetime import datetime
from uuid import UUID, uuid4