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Python Code Samples

Copy-ready Python snippets by topic and difficulty — short, focused, and runnable in the browser editor.

5 matches
Concurrency & performance medium

How to Mock anyio.run Backends (asyncio vs trio) in Python

Demonstrates how to mock anyio.run to verify backend selection (asyncio or trio) without actually running the event loop.

anyio async testing
Python 
import anyio
from unittest.mock import Mock, patch


async def fetch_data():
    await anyio.sleep(0.1)
    return {"data": 42}


def run_with_backend(backend: str):
    async def main():
        result = await fetch_data()
        print(f"[{backend}] Result: {result}")

    anyio.run(main, backend=backend)


if __nam…
14 0 Open
Concurrency & performance medium

How to Run Blocking Code in an Executor with asyncio in Python

This code runs blocking functions concurrently without stalling the event loop by offloading them to thread pool executors via asyncio.

asyncio executor concurrency
Python 
import asyncio
import time


def blocking_task(name: str, duration: float) -> str:
    """Simulate a blocking operation."""
    time.sleep(duration)
    return f"Finished {name} after {duration}s"


async def main() -> None:
    loop = asyncio.get_running_loop()
    results = await asyncio.gather(
        loop.run_in_…
14 0 Open
Concurrency & performance easy

How to Run an Async Main with asyncio.run in Python

Show the canonical entry point for an asyncio program: define an async main, then launch it with asyncio.run.

asyncio event loop entry point
Python 
import asyncio


async def main():
    print("Hello from async main")
    await asyncio.sleep(0.1)
    print("Done")


if __name__ == "__main__":
    asyncio.run(main())
16 0 Open
Concurrency & performance easy

How to Use uvloop Faster Event Loop

Install uvloop at startup to replace asyncio's default event loop with a faster libuv-based one, with a graceful fallback when it's unavailable.

uvloop asyncio event-loop
Python 
import asyncio
try:
    import uvloop
    uvloop.install()
    USING_UVLOOP = True
except ImportError:
    USING_UVLOOP = False


async def fetch_data(index):
    await asyncio.sleep(0.01)
    return f"data-{index}"


async def main():
    tasks = [fetch_data(i) for i in range(10)]
    results = await asyncio.gather(*…
14 0 Open
Concurrency & performance easy

Run Background Tasks with asyncio.create_task in Python

Create background tasks in an asyncio event loop with asyncio.create_task and run them concurrently using asyncio.gather.

asyncio async concurrency
Python 
import asyncio
import time

async def background_worker(name, duration):
    """Simulates a long-running background task."""
    print(f"{name} started at t={time.monotonic():.1f}")
    await asyncio.sleep(duration)
    print(f"{name} finished at t={time.monotonic():.1f}")

async def main():
    print(f"Main starting …
13 0 Open

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