get2knowio/maverick-python-async

Python Async/Await Skill

Expert guidance for asynchronous Python programming with asyncio.

Core Concepts

Async Functions (Coroutines)

async def fetch_data(url: str) -> dict:
    """Async function returns a coroutine."""
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as response:
            return await response.json()

Running Async Code

import asyncio

# Python 3.7+
asyncio.run(main())

# Or event loop (older style)
loop = asyncio.get_event_loop()
loop.run_until_complete(main())

Common Patterns

Concurrent Execution

# gather - run concurrently, wait for all
results = await asyncio.gather(
    fetch_data(url1),
    fetch_data(url2),
    fetch_data(url3),
)

# create_task - run in background
task1 = asyncio.create_task(fetch_data(url1))
task2 = asyncio.create_task(fetch_data(url2))
result1 = await task1
result2 = await task2

Timeouts

try:
    result = await asyncio.wait_for(
        slow_operation(),
        timeout=5.0
    )
except asyncio.TimeoutError:
    print("Operation timed out")

Async Context Managers

async with aiohttp.ClientSession() as session:
    async with session.get(url) as response:
        data = await response.text()

Async Iterators

async for item in async_generator():
    process(item)

Antipatterns

❌ Blocking Calls in Async Functions

# BAD - blocks event loop
async def bad():
    time.sleep(1)  # BLOCKS!
    response = requests.get(url)  # BLOCKS!

# GOOD - use async alternatives
async def good():
    await asyncio.sleep(1)
    async with aiohttp.ClientSession() as session:
        response = await session.get(url)

❌ Not Awaiting Coroutines

# BAD - coroutine never executes
async def bad():
    fetch_data()  # Missing await!

# GOOD
async def good():
    await fetch_data()

❌ Creating Too Many Tasks

# BAD - creates 10000 tasks at once
tasks = [asyncio.create_task(fetch(url)) for url in urls]

# GOOD - use semaphore to limit concurrency
async def fetch_with_limit(url, semaphore):
    async with semaphore:
        return await fetch(url)

semaphore = asyncio.Semaphore(10)
tasks = [fetch_with_limit(url, semaphore) for url in urls]

Review Severity

• CRITICAL: Blocking calls in async functions (time.sleep, requests.get)
• MAJOR: Missing await on coroutines, not handling asyncio.CancelledError
• MINOR: Not using async context managers, inefficient gather usage