如何从同步代码 Python 调用异步函数

Question

所以我被锁定在我的桌面应用程序后面的 python 3.6.2 解释器上。

我想要的是从同步方法或函数调用异步函数。

当从桌面应用程序调用 python 函数时，它必须是一个不能等待的普通函数。

我可以从桌面应用程序发送一个 url 列表，我想要的是从异步事件中的每个 url 发回响应。

这是我的尝试，我标记了我不知道如何绕过的 SyntaxError。

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

我曾尝试进行这些更改：

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]


        

但现在我最终遇到了这个错误：

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 答案可能是您在 Python 3.6 中能做的最好的。 但是在 Python 3.7 中，您可以通过以下方式直接使用asyncio.run ：

newfeature = asyncio.run(main(urls))

它将正确创建、处理和关闭event_loop 。

Answer 2

您将使用事件循环来执行异步函数以完成：

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

（这个技术已经在main 。我不知道为什么，因为main是async你可以/应该await fetch_all(...)使用await fetch_all(...) 。）

Answer 3

另一个可能有用的选项是syncer PyPI 包：

from syncer import sync

@sync
async def print_data():
    print(await get_data())

print_data()  # Can be called synchronously