20. asyncio Event Loop Masterclass: Coroutines, Tasks & asyncio.gather • Python 0-to-Hero Mastery (Big Tech SDE & ML Standard) • Rishabh Ki Kaksha

Single-threaded cooperative multitasking! Jab koi operation I/O ke liye wait karta hai (`await`), control instantly Event Loop ko pass ho jata hai jo doosre ready tasks execute karta hai:

```python
import asyncio
import httpx

async def fetch_api(client: httpx.AsyncClient, endpoint: str):
    response = await client.get(endpoint)
    return response.json()

async def main():
    async with httpx.AsyncClient() as client:
        # Run 100 API calls concurrently in < 1 second!
        tasks = [fetch_api(client, f"https://api.example.com/item/{i}") for i in range(100)]
        results = await asyncio.gather(*tasks, return_exceptions=True)
        print(f"Fetched {len(results)} items!")

asyncio.run(main())
```

---

### 2. `asyncio.TaskGroup` (Python 3.11+ Structured Concurrency 👑)

```python
async with asyncio.TaskGroup() as tg:
    task1 = tg.create_task(service_a())
    task2 = tg.create_task(service_b())
# If task1 fails, task2 is automatically cancelled cleanly!
```

---

### 3. Interview Ke 3 Sawal Is Topic Se

1. **Async code me blocking call (`time.sleep()` ya synchronous `requests.get()`) execute karne se kya hota hai?** -> Poora Event Loop freeze ho jata hai aur saare concurrent users block ho jaate hain (Always use `asyncio.to_thread()` for legacy blocking code).
2. **`asyncio.gather()` vs `asyncio.as_completed()` me kya farak hai?** -> `gather` saare tasks complete hone tak wait karke batch list return karta hai; `as_completed` jaise-jaise individual task finish hota hai turant yield karta hai.
3. **UVLoop third-party library asyncio ko 3x fast kaise banati hai?** -> Python C-extension event loop written in C on top of `libuv` (Same engine as Node.js).

---
**Next Topic:** 21. File I/O, Serialization (JSON, Pickle) & Pathlib Architecture

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1 Questions

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1. Concurrent Microservices Aggregator

`asyncio.gather` ka use karke 3 asynchronous endpoints ka data simultaneously load karein.

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• Use asyncio.gather with await.

Python 3.12

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1. Concurrent Microservices Aggregator

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Rishabh Gehlot

PHP 8+ & Laravel 11 Master Track