ReddRadar
Agent skill
python-async-patterns
Python asyncio patterns for concurrent programming. Triggers on: asyncio, async, await, coroutine, gather, semaphore, TaskGroup, event loop, aiohttp, concurrent.
Install this agent skill to your Project
npx add-skill https://github.com/aiskillstore/marketplace/tree/main/skills/0xdarkmatter/python-async-patterns
SKILL.md
Python Async Patterns
Asyncio patterns for concurrent Python programming.
Core Concepts
import asyncio
# Coroutine (must be awaited)
async def fetch(url: str) -> str:
async with aiohttp.ClientSession() as session:
async with session.get(url) as response:
return await response.text()
# Entry point
async def main():
result = await fetch("https://example.com")
return result
asyncio.run(main())
Pattern 1: Concurrent with gather
async def fetch_all(urls: list[str]) -> list[str]:
"""Fetch multiple URLs concurrently."""
async with aiohttp.ClientSession() as session:
tasks = [fetch_one(session, url) for url in urls]
return await asyncio.gather(*tasks, return_exceptions=True)
Pattern 2: Bounded Concurrency
async def fetch_with_limit(urls: list[str], limit: int = 10):
"""Limit concurrent requests."""
semaphore = asyncio.Semaphore(limit)
async def bounded_fetch(url):
async with semaphore:
return await fetch_one(url)
return await asyncio.gather(*[bounded_fetch(url) for url in urls])
Pattern 3: TaskGroup (Python 3.11+)
async def process_items(items):
"""Structured concurrency with automatic cleanup."""
async with asyncio.TaskGroup() as tg:
for item in items:
tg.create_task(process_one(item))
# All tasks complete here, or exception raised
Pattern 4: Timeout
async def with_timeout():
try:
async with asyncio.timeout(5.0): # Python 3.11+
result = await slow_operation()
except asyncio.TimeoutError:
result = None
return result
Critical Warnings
# WRONG - blocks event loop
async def bad():
time.sleep(5) # Never use time.sleep!
requests.get(url) # Blocking I/O!
# CORRECT
async def good():
await asyncio.sleep(5)
async with aiohttp.ClientSession() as s:
await s.get(url)
# WRONG - orphaned task
async def bad():
asyncio.create_task(work()) # May be garbage collected!
# CORRECT - keep reference
async def good():
task = asyncio.create_task(work())
await task
Quick Reference
| Pattern | Use Case |
|---|---|
gather(*tasks) |
Multiple independent operations |
Semaphore(n) |
Rate limiting, resource constraints |
TaskGroup() |
Structured concurrency (3.11+) |
Queue() |
Producer-consumer |
timeout(s) |
Timeout wrapper (3.11+) |
Lock() |
Shared mutable state |
Async Context Manager
from contextlib import asynccontextmanager
@asynccontextmanager
async def managed_connection():
conn = await create_connection()
try:
yield conn
finally:
await conn.close()
Additional Resources
For detailed patterns, load:
./references/concurrency-patterns.md- Queue, Lock, producer-consumer./references/aiohttp-patterns.md- HTTP client/server patterns./references/mixing-sync-async.md- run_in_executor, thread pools./references/debugging-async.md- Debug mode, profiling, finding issues./references/production-patterns.md- Graceful shutdown, health checks, signal handling./references/error-handling.md- Retry with backoff, circuit breakers, partial failures./references/performance.md- uvloop, connection pooling, buffer sizing
Scripts
./scripts/find-blocking-calls.sh- Scan code for blocking calls in async functions
Assets
./assets/async-project-template.py- Production-ready async app skeleton
See Also
Prerequisites:
python-typing-patterns- Type hints for async functions
Related Skills:
python-fastapi-patterns- Async web APIspython-observability-patterns- Async logging and tracingpython-database-patterns- Async database access
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