使用 asyncio 及时更新一些数据并通过 aiohttp 呈现?
use asyncio update some data timely and present via aiohttp?
我正在尝试编写一个片段来研究 Python asyncio。基本思路是:
使用 "simple" 网络服务器 (aiohttp) 向用户呈现一些数据
给用户的数据return会及时更改
代码如下:
import asyncio
import random
from aiohttp import web
userfeed = [] # the data suppose to return to the user via web browsers
async def data_updater(): #to simulate data change promptly
while True:
await asyncio.sleep(3)
userfeed = [x for x in range(random.randint(1, 20))]
print('user date updated: ', userfeed)
async def web_handle(request):
text = str(userfeed)
#print('in handler:', text) # why text is empty?
return web.Response(text=text)
async def init(loop):
app = web.Application(loop=loop)
app.router.add_route('GET', '/', web_handle)
srv = await loop.create_server(app.make_handler(), '127.0.0.1', 8000)
print('Server started @ http://127.0.0.1:8000...')
return srv
loop = asyncio.get_event_loop()
asyncio.ensure_future(data_updater())
asyncio.ensure_future(init(loop))
loop.run_forever()
问题是,代码是 运行 (python 3.5),但是 userfeed
在浏览器和 web_handler()
中总是空的 :-(
- 为什么
userfeed
没有更新? - 关于这个
timely date update
函数,因为后面更新机制可能比较复杂,说可能涉及到async IO wait,有没有更好的方法代替data_updater()
中的while True: await asyncio.sleep(3)
获取 "more roughly precise" 计时器?
主要问题是您忘记了 data_updater
和 web_handle
函数中的语句 global userfeed
。因此,根据 how python resolves scopes, in web_handle
it was referring to the global variable you defined and in data_updater
to a local one, created by the statement userfeed = [x for x ...
. Using global variables in this context is explicitly discouraged,有一个示例使用 aiohttp.web.Application
对象的 dict
接口在函数之间安全地引用您的变量。
import asyncio
import random
from aiohttp import web
async def data_updater(app):
while True:
await asyncio.sleep(3)
app["userfeed"] = [x for x in range(random.randint(1, 20))]
async def web_handle(request):
userfeed = request.app["userfeed"]
return web.Response(text=str(userfeed))
async def init(loop, port=8000):
app = web.Application(loop=loop)
app.router.add_route('GET', '/', web_handle)
handler = app.make_handler()
srv = await loop.create_server(
handler, '127.0.0.1', port=port)
return srv, app, handler
if __name__ == "__main__":
loop = asyncio.get_event_loop()
srv, app, handler = loop.run_until_complete(init(loop, 8000))
app['userfeed'] = []
asyncio.ensure_future(data_updater(app))
try:
loop.run_forever()
except KeyboardInterrupt:
pass
finally:
srv.close()
loop.run_until_complete(srv.wait_closed())
loop.run_until_complete(app.shutdown())
loop.run_until_complete(handler.finish_connections(60.0))
loop.run_until_complete(app.cleanup())
loop.close()
当您在 127.0.0.1:8000
刷新页面时,您应该有一些新的随机数,因为它们在服务器端每 3 秒更新一次(您可以在 [=12= 中放回 print
语句] 来验证)。