How to call a async function from a synchronized code Python

Question

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 

Answer 1

@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.

Answer 2

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.)