python-django

REQUIRED BACKGROUND: This skill depends_on: [clean-code, backend-fundamentals]. Both are loaded transitively — clean-code gives universal code quality (fail-closed errors, typed exceptions, self-documenting code, edge cases, error path tests) and backend-fundamentals gives stack-agnostic backend patterns (services/selectors, idempotency, envelopes, N+1, migrations, auth). This skill adds ONLY Django/DRF-specific layering on top.

Pre-Code Checklist

Before writing any backend Python code, verify:

• Read docs/engineering/backend-rules.md — the canonical backend policy
• If touching models or schema: read docs/prd/12a-commerce-schema.md and docs/prd/12b-content-and-system-schema.md
• If touching API endpoints or error handling: read docs/api-contracts/error-format.md
• If touching auth, payments, file uploads, or permissions: read docs/playbooks/security-review.md
• If touching download infrastructure: read docs/architecture/04c-download-security.md
• Search the repo with Grep/Glob for existing code before creating any new file

1. Architecture: Services + Selectors

Views are thin dispatchers. All business logic lives in services (writes) and selectors (reads).

Layer Responsibilities

Correct Pattern

# apps/products/views/product_views.py
from rest_framework.views import APIView
from rest_framework.response import Response
from rest_framework import status

from apps.products.selectors import product_selectors
from apps.products.serializers import ProductDetailSerializer


class ProductDetailView(APIView):
    """Thin view — delegates to selector, serializes, returns."""

    def get(self, request, slug: str) -> Response:
        product = product_selectors.get_published_product(slug=slug)
        serializer = ProductDetailSerializer(product)
        return Response(serializer.data, status=status.HTTP_200_OK)