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Async Support in Flask

Understand async support in Flask

Prior to version 2.0, Flask does not provide native support for asynchronous programming. However, you can use Python's asyncio library in conjunction with Flask to achieve asynchronous behavior when needed.

Understand async support in Flask - Tutorial provided by AppSeed.

Flask is traditionally a synchronous framework, but you can integrate asynchronous code as required.

For those that are forced to use legacy versions of Flask, here's how you can work with asynchronous code in Flask:

✅ Using asyncio​

You can use Python's asyncio library to handle asynchronous operations within your Flask application. Here's a simple example of how you might use asyncio in a Flask route:

from flask import Flask
import asyncio

app = Flask(__name__)

@app.route('/')
async def async_route():
    result = await some_async_function()
    return f'Result: {result}'

async def some_async_function():
    await asyncio.sleep(2)  # Simulating an asynchronous operation
    return 'Async data'

if __name__ == '__main__':
    app.run()

In this example, the async_route function is marked as async, and it awaits the result of an asynchronous operation within some_async_function. The route handler will not block, allowing the server to handle other requests during the waiting period.

✅ Using Flask with gevent​

Another way to achieve asynchronous behavior in Flask is to use the gevent library, which provides a cooperative multitasking environment. Gevent can be used as a WSGI server for Flask, allowing it to handle multiple requests concurrently.

First, install gevent:

pip install gevent

Then, you can use gevent with Flask like this:

from flask import Flask
from gevent.pywsgi import WSGIServer

app = Flask(__name__)

@app.route('/')
def hello():
    return 'Hello, World!'

if __name__ == '__main__':
    http_server = WSGIServer(('0.0.0.0', 5000), app)
    http_server.serve_forever()

In this example, the gevent-based WSGIServer enables multiple requests to be handled concurrently without blocking.

✅ In Summary​

Please note that asynchronous programming is typically used for I/O-bound operations to improve the responsiveness and efficiency of your web application. Flask is well-suited for such use cases when combined with appropriate asynchronous libraries like asyncio or gevent.

However, for CPU-bound tasks, you might want to explore other asynchronous frameworks like FastAPI, which has native support for asynchronous programming.

✅ Resources​