python3.5.2怎么使用_如何在python3.5.2中使用gather

我试图学习如何用python编写asnycron编程，并编写了一个小tornado应用程序，它用sleep命令执行两个asnycron循环。

如果我用两个await命令等待两个协程，那么它的行为与预期的一样(第一个循环，而不是第二个循环被执行)

如果我将这两个协同路径与聚集结合在一起，则什么都不会发生。(没有错误，没有打印输出，Web请求从未完成。)

我不明白*await gather发生了什么(coros，return_exceptions=True)from asyncio import gather

import os.path

import tornado.ioloop

from tornado.options import define, options, parse_command_line

import tornado.web

import tornado.platform.asyncio

from tornado.gen import sleep

import datetime;

define("port", default=8888, help="run on the given port", type=int)

define("debug", default=False, help="run in debug mode")

class AsyncTestHandler(tornado.web.RequestHandler):

async def get(self):

operation = self.get_query_argument('operation')

if operation == 'with_two_waits':

await self._with_two_waits()

elif operation == 'with_gather':

await self._with_gather()

else:

self.finish('use operation=with_two_waits or operation=with_gather')

return

self.finish('finished ' + operation);

async def _with_two_waits(self):

print('_with_two_waits: start' + str(datetime.datetime.now()) )

w1 = self._wait_loop("First loop", 8)

w2 = self._wait_loop("Second loop", 6)

await w1

await w2

print('_with_two_waits: finished' + str(datetime.datetime.now()))

async def _with_gather(self):

print('_with_gather: start' + str(datetime.datetime.now()))

coros = []

coros.append(self._wait_loop("First loop", 8))

coros.append(self._wait_loop("Second loop", 6))

await gather(*coros, return_exceptions=True)

print ('_with_gather: finished' + str(datetime.datetime.now()))

async def _wait_loop(self, loop_name, count):

for i in range(1, count + 1):

print(loop_name + ' ' + str(i) + '/' + str(count) + ' ' + str(datetime.datetime.now()))

await sleep(0.1)

print(loop_name + ' complete')

def start_web_app():

parse_command_line()

app = tornado.web.Application(

[

(r"/asnycTest", AsyncTestHandler),

],

debug=options.debug,

)

app.listen(options.port)

tornado.ioloop.IOLoop.current().start()

if __name__ == "__main__":

start_web_app()