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Asyncio Mini Project (Concurrent URL checker)

Goal

Build a script that:

checks many URLs
runs requests concurrently
returns status codes
uses timeouts and a concurrency limit

Implementation

url_checker.py

import asyncio
import aiohttp
 
 
async def fetch(session: aiohttp.ClientSession, sem: asyncio.Semaphore, url: str):
    async with sem:
        try:
            async with session.get(url) as resp:
                await resp.read()
                return url, resp.status
        except Exception as e:
            return url, str(e)
 
 
async def main():
    urls = [
        "https://api.github.com",
        "https://httpbin.org/status/404",
        "https://httpbin.org/delay/2",
        "https://example.com",
    ]
 
    sem = asyncio.Semaphore(5)
    timeout = aiohttp.ClientTimeout(total=5)
 
    async with aiohttp.ClientSession(timeout=timeout) as session:
        results = await asyncio.gather(*(fetch(session, sem, u) for u in urls))
 
    for url, status in results:
        print(url, "->", status)
 
 
if __name__ == "__main__":
    asyncio.run(main())

url_checker.py

import asyncio
import aiohttp
 
 
async def fetch(session: aiohttp.ClientSession, sem: asyncio.Semaphore, url: str):
    async with sem:
        try:
            async with session.get(url) as resp:
                await resp.read()
                return url, resp.status
        except Exception as e:
            return url, str(e)
 
 
async def main():
    urls = [
        "https://api.github.com",
        "https://httpbin.org/status/404",
        "https://httpbin.org/delay/2",
        "https://example.com",
    ]
 
    sem = asyncio.Semaphore(5)
    timeout = aiohttp.ClientTimeout(total=5)
 
    async with aiohttp.ClientSession(timeout=timeout) as session:
        results = await asyncio.gather(*(fetch(session, sem, u) for u in urls))
 
    for url, status in results:
        print(url, "->", status)
 
 
if __name__ == "__main__":
    asyncio.run(main())

Improvements

read URLs from a file
write results to CSV
add retries with exponential backoff

🧪 Try It Yourself

Exercise 1 – Your First Coroutine

Exercise 2 – await asyncio.sleep

Exercise 3 – Gather Two Coroutines

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