从Flask路由进行Python异步调用 [英] Make a Python asyncio call from a Flask route

问题描述

我想在每次执行Flask路由时执行一个异步函数.为什么abar函数从不执行?

I want to execute an async function every time the Flask route is executed. Why is the abar function never executed?

import asyncio
from flask import Flask

async def abar(a):
    print(a)

loop = asyncio.get_event_loop()
app = Flask(__name__)

@app.route("/")
def notify():
    asyncio.ensure_future(abar("abar"), loop=loop)
    return "OK"

if __name__ == "__main__":
    app.run(debug=False, use_reloader=False)
    loop.run_forever()

我还尝试将阻塞调用放在单独的线程中.但是它仍然没有调用abar函数.

I also tried putting the blocking call in a separate thread. But it is still not calling the abar function.

import asyncio
from threading import Thread
from flask import Flask

async def abar(a):
    print(a)

app = Flask(__name__)

def start_worker(loop):
    asyncio.set_event_loop(loop)
    try:
        loop.run_forever()
    finally:
        loop.close()

worker_loop = asyncio.new_event_loop()
worker = Thread(target=start_worker, args=(worker_loop,))

@app.route("/")
def notify():
    asyncio.ensure_future(abar("abar"), loop=worker_loop)
    return "OK"

if __name__ == "__main__":
    worker.start()
    app.run(debug=False, use_reloader=False)

推荐答案

您可以将一些异步功能集成到Flask应用程序中，而不必完全将其转换为asyncio.

You can incorporate some async functionality into Flask apps without having to completely convert them to asyncio.

import asyncio
from flask import Flask

async def abar(a):
    print(a)

loop = asyncio.get_event_loop()
app = Flask(__name__)

@app.route("/")
def notify():
    loop.run_until_complete(abar("abar"))
    return "OK"

if __name__ == "__main__":
    app.run(debug=False, use_reloader=False)

这将阻止Flask响应，直到异步函数返回为止，但是它仍然允许您做一些聪明的事情.我已经使用此模式使用 aiohttp 并行执行许多外部请求，然后在它们完成后，我回到传统的烧瓶中进行数据处理和模板渲染.

This will block the Flask response until the async function returns, but it still allows you to do some clever things. I've used this pattern to perform many external requests in parallel using aiohttp, and then when they are complete, I'm back into traditional flask for data processing and template rendering.

import aiohttp
import asyncio
import async_timeout
from flask import Flask

loop = asyncio.get_event_loop()
app = Flask(__name__)

async def fetch(url):
    async with aiohttp.ClientSession() as session, async_timeout.timeout(10):
        async with session.get(url) as response:
            return await response.text()

def fight(responses):
    return "Why can't we all just get along?"

@app.route("/")
def index():
    # perform multiple async requests concurrently
    responses = loop.run_until_complete(asyncio.gather(
        fetch("https://google.com/"),
        fetch("https://bing.com/"),
        fetch("https://duckduckgo.com"),
        fetch("http://www.dogpile.com"),
    ))

    # do something with the results
    return fight(responses)

if __name__ == "__main__":
    app.run(debug=False, use_reloader=False)

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