python-backend

name	python-backend
license	MIT
compatibility	Claude Code 2.1.220+.
description	Production Python async patterns including asyncio TaskGroup, FastAPI dependency injection and middleware, SQLAlchemy 2.0 async sessions, and database connection pool tuning. Python 3.11+ runtime concerns such as ExceptionGroup, cancellation semantics, and session rollback. Use when building async services, wiring FastAPI dependencies, or tuning database connection pools. Runtime implementation layer, not the API wire contract.
tags	["python","asyncio","fastapi","sqlalchemy","connection-pooling","async","postgresql"]
context	fork
agent	backend-system-architect
version	2.0.0
author	OrchestKit
user-invocable	false
disable-model-invocation	false
complexity	medium
persuasion-type	reference
targets	[{"library":"fastapi","version":">=0.100.0"},{"library":"sqlalchemy","version":">=2.0.0"}]
metadata	{"category":"document-asset-creation"}
allowed-tools	["Read","Glob","Grep","WebFetch","WebSearch"]
path_patterns	["*.py","**/requirements*.txt","**/pyproject.toml","**/Pipfile"]

Python Backend

Patterns for building production Python backends with asyncio, FastAPI, SQLAlchemy 2.0, and connection pooling. Each category has individual rule files in rules/ loaded on-demand.

Quick Reference

Category	Rules	Impact	When to Use
Asyncio	3	HIGH	TaskGroup, structured concurrency, cancellation handling
FastAPI	3	HIGH	Dependencies, middleware, background tasks
SQLAlchemy	3	HIGH	Async sessions, relationships, migrations
Pooling	3	MEDIUM	Database pools, HTTP sessions, tuning

Total: 12 rules across 4 categories. House decisions rescued from thinned files live in references/ork-delta.md; vendor material is linked, not restated (see Upstream coverage).

Quick Start

# FastAPI + SQLAlchemy async session
async def get_db() -> AsyncGenerator[AsyncSession, None]:
    async with async_session_factory() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise

# Reusable dependency alias (FastAPI's recommended Annotated form)
SessionDep = Annotated[AsyncSession, Depends(get_db)]

@router.get("/users/{user_id}")
async def get_user(user_id: UUID, db: SessionDep):
    result =  db.execute(select(User).where(User. == user_id))
     result.scalar_one_or_none()