Unexpected Behavior When Using Asyncio with Flask in Python 3.10
I just started working with I've been struggling with this for a few days now and could really use some help... I'm currently trying to integrate `asyncio` into my Flask application (using Flask 2.0.1 and Python 3.10) to handle some I/O-bound tasks without blocking the main thread. However, I'm encountering unexpected behavior when attempting to make asynchronous calls to a database using SQLAlchemy. Here's a simplified version of my code: ```python from flask import Flask, jsonify from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine from sqlalchemy.orm import sessionmaker import asyncio app = Flask(__name__) DATABASE_URL = 'postgresql+asyncpg://user:password@localhost/dbname' engine = create_async_engine(DATABASE_URL, echo=True) AsyncSessionLocal = sessionmaker(bind=engine, class_=AsyncSession, expire_on_commit=False) @app.route('/async-data') async def async_data(): async with AsyncSessionLocal() as session: result = await session.execute('SELECT * FROM my_table') data = result.fetchall() return jsonify(data) if __name__ == '__main__': app.run() ``` When I try to access the `/async-data` endpoint, I receive the following error: ``` RuntimeError: This event loop is already running ``` I have also tried wrapping the `async_data` function in a separate event loop context, but that leads to another error regarding the event loop policies. I found that Flask's built-in server doesn't support async functions out of the box in versions prior to Flask 2.0. I’ve read that using `flask[async]` might help, but I’m not clear on how to implement that correctly. Could someone provide insights or best practices for properly integrating `asyncio` with Flask in this context? Any specific configurations or recommendations would be greatly appreciated! My development environment is Ubuntu. Is there a better approach? For reference, this is a production service. Thanks for taking the time to read this!