How to call a async function from a synchronized code Python

问题

So I'm locked to a python 3.6.2 interpreter that follows my desktop application.

What I want is to call an async function from a synchronized method or function.

When calling the python function from the desktop application it has to be a normal function which can not be awaited.

From the desktop application I am able to send a list of urls, and what I want is to send back response from every url in an async matter.

here is my try I've marked the SyntaxError which I don't know how to bypass.

import fmeobjects
import asyncio
import aiohttp
import async_timeout
logger = fmeobjects.FMELogFile()
timeout = 10

class FeatureProcessor(object):
    def __init__(self):
        pass
    def input(self, feature):
        urls_and_coords = zip(feature.getAttribute('_list{}._wms'),\
        feature.getAttribute('_list{}._xmin'),\
        feature.getAttribute('_list{}._ymin'),\
        feature.getAttribute('_list{}._xmax'),\
        feature.getAttribute('_list{}._ymax'))
        -> SyntaxError: newfeature = await main(urls_and_coords)
        self.pyoutput(newfeature)

    def close(self):
       pass 

async def main(urls):
    loop = asyncio.get_event_loop()
    async with aiohttp.ClientSession(loop=loop) as session:
        feature = loop.run_until_complete(fetch_all(session, urls, loop))
        return feature

async def fetch_all(session, urls, loop):
    results = await asyncio.gather(*[loop.create_task(fetch(session, url)) for url in urls])
    return results


async def fetch(session, url):
    with async_timeout.timeout(10):
        async with session.get(url[0]) as response:
            newFeature = fmeobjects.FMEFeature()
            response_data = await response
            newFeature.setAttribute('response', response_data)
            newFeature.setAttribute('_xmin',url[1])
            newFeature.setAttribute('_xmax',url[2])
            newFeature.setAttribute('_ymin',url[3])
            newFeature.setAttribute('_ymax',url[4])
            return newFeature

I have tried making these changes: import fme import fmeobjects import asyncio import aiohttp import async_timeout logger = fmeobjects.FMELogFile()

class FeatureProcessor(object):
    def __init__(self):
        pass
    def input(self, feature):
        urls_and_coords = zip(feature.getAttribute('_list{}._wms'),\
        feature.getAttribute('_list{}._xmin'),\
        feature.getAttribute('_list{}._ymin'),\
        feature.getAttribute('_list{}._xmax'),\
        feature.getAttribute('_list{}._ymax'))
        loop = asyncio.get_event_loop()
        result = loop.run_until_complete(main(loop, urls_and_coords))
        #feature.setAttribute('result',result)
        self.pyoutput(feature)

    def close(self):
       pass 

async def main(loop, urls):
    async with aiohttp.ClientSession(loop=loop) as session:
        return await fetch_all(session, urls, loop)


async def fetch_all(session, urls, loop):
    results = await asyncio.gather(*[loop.create_task(fetch(session, url)) for url in urls])
    return results


async def fetch(session, url):
    with async_timeout.timeout(10):
        async with session.get(url[0]) as response:
            #newFeature = fmeobjects.FMEFeature()
            response = await response
            #newFeature.setAttribute('response', response_data)
            #newFeature.setAttribute('_xmin',url[1])
            #newFeature.setAttribute('_xmax',url[2])
            #newFeature.setAttribute('_ymin',url[3])
            #newFeature.setAttribute('_ymax',url[4])
            return response, url[1], url[2], url[3], url[4]

but now I end up with this error:

Python Exception <TypeError>: object ClientResponse can't be used in 'await' 
expression
Traceback (most recent call last):
  File "<string>", line 20, in input
  File "asyncio\base_events.py", line 467, in run_until_complete
  File "<string>", line 29, in main
  File "<string>", line 33, in fetch_all
  File "<string>", line 41, in fetch
TypeError: object ClientResponse can't be used in 'await' expression

回答1:

You would use an event loop to execute the asynchronous function to completion:

newfeature = asyncio.get_event_loop().run_until_complete(main(urls_and_coords))

(This technique is already used inside main. And I'm not sure why, since main is async you could/should use await fetch_all(...) there.)

回答2:

@deceze answer is probably the best you can do in Python 3.6. But in Python 3.7, you could directly use asyncio.run in the following way:

newfeature = asyncio.run(main(urls))

It will properly create, handle, and close an event_loop.

来源：https://stackoverflow.com/questions/51762227/how-to-call-a-async-function-from-a-synchronized-code-python