Python的asyncio,期货和收益率

考虑以下程序(在CPython 3.4.0b1上运行):

import math
import asyncio
from asyncio import coroutine

@coroutine
def fast_sqrt(x):
   future = asyncio.Future()
   if x >= 0:
      future.set_result(math.sqrt(x))
   else:
      future.set_exception(Exception("negative number"))
   return future


def slow_sqrt(x):
   yield from asyncio.sleep(1)
   future = asyncio.Future()
   if x >= 0:
      future.set_result(math.sqrt(x))
   else:
      future.set_exception(Exception("negative number"))
   return future


@coroutine
def run_test():
   for x in [2, -2]:
      for f in [fast_sqrt, slow_sqrt]:
         try:
            future = yield from f(x)
            print("\n{} {}".format(future, type(future)))
            res = future.result()
            print("{} result: {}".format(f, res))
         except Exception as e:
            print("{} exception: {}".format(f, e))


loop = asyncio.get_event_loop()
loop.run_until_complete(run_test())

我有2个(相关)问题:

即使启动了装饰器fast_sqrt,Python似乎也fast_sqrt完全消除了创建的Future ,并float返回了plain .然后在炸毁run_test()的yield from

为什么我需要评估future.result()在run_test检索火的值例外呢？该文件说,yield from "暂停协程,直到将来完成,然后返回未来的结果,或将引发异常".为什么我需要手动解决未来的结果？

这是我得到的:

oberstet@COREI7 ~/scm/tavendo/infrequent/scratchbox/python/asyncio (master)
$ python3 -V
Python 3.4.0b1
oberstet@COREI7 ~/scm/tavendo/infrequent/scratchbox/python/asyncio (master)
$ python3 test3.py

1.4142135623730951 
 exception: 'float' object has no attribute 'result'

Future 
 result: 1.4142135623730951
 exception: negative number

Future 
 exception: negative number
oberstet@COREI7 ~/scm/tavendo/infrequent/scratchbox/python/asyncio (master)

好的,我找到了"问题".将yield from asyncio.sleep在slow_sqrt会使其自动协同程序.等待需要以不同的方式完成:

def slow_sqrt(x):
   loop = asyncio.get_event_loop()
   future = asyncio.Future()
   def doit():
      if x >= 0:
         future.set_result(math.sqrt(x))
      else:
         future.set_exception(Exception("negative number"))
   loop.call_later(1, doit)
   return future

所有4个变种都在这里.