Achieving Concurrency in Python Web Frameworks

Python web frameworks like Django and Flask handle multiple simultaneous requests through concurrency instead of parallelism.

This means they use a single thread and asynchronous I/O to juggle multiple requests, rather than multiple threads/processes. Here's how it works under the hood:

import asyncio

async def handle_request(request):
    response = # do something with request
    return response

async def main():
    await asyncio.gather(
        handle_request(req1),
        handle_request(req2)  
    )

The asyncio module and async/await syntax enable a single-threaded web server to await I/O bound tasks like database/network operations. This allows other requests to be handled while waiting, achieving concurrency with just one thread.

The advantage over multi-threading is avoiding lock contention and simplified code. The tradeoff is CPU-bound tasks still execute sequentially. But most web workloads tend to be I/O heavy anyway.