协程之生成器yield from

yield from 你知道做什么那些事情吗？

帮我们迭代：

#python3.3新加了yield from语法
from itertools import chain

my_list = [1,2,3]
my_dict = {
"sunlong001":"http://baidu1.com",
"sunlong002":"http://www.baidu2.com",
}

def my_chain(*args, **kwargs):
for my_iterable in args:
# yield from my_iterable
for value in my_iterable:
yield value

for value in my_chain(my_list, my_dict, range(5,10)):
print(value)

yield from my_iterable等价于：

for value in my_iterable:
yield value

 让协程返回值

#让协程返回值
#定义一个求平均值的协程
from collections import namedtuple
Result = namedtuple('Result','cunt average')
def averager():
total = 0
count = 0
average = None
while True:
term = yield
if term is None:
break
total += term
count += 1
average = total/count
return Result(count,average)

coro_avg = averager()
coro_avg.send(None)
coro_avg.send(10)
coro_avg.send(20)
coro_avg.send(9)
# coro_avg.send(None)

try:
coro_avg.send(None)
except StopIteration as exc:
result = exc.value

print(result)

yield from的主要功能是打开双向通道，把最外层的调用方法与最内层的子生成器连接起来，这样二者可以直接发送和产出值，还可以直接传入异常，而不用在位于中间的协程中添加大量处理异常的代码，有了这个机构，

协程可以通过以前不可能的方式委托职责

委派生成器；

子生成器；

委派生成器在yield from 表达式处暂停时，调用放可以直接把数据发给子生成器，子生成器再把产出的值发给调用方，子生成其返回之后，解释器会抛出StopIteration异常，并把返回值附加到异常对象上，此时委派生成器会恢复

#让协程返回值
#定义一个求平均值的协程
from collections import namedtuple
Result = namedtuple('Result','cunt average')

#子生成器
def averager():
total = 0
count = 0
average = None
while True:
term = yield
if term is None:
break
total += term
count += 1
average = total/count
return Result(count,average)

#委派生成器
def grouper(results,key):
while True:
results[key] = yield from averager()


#客户端代码 调用方
def main(data):
results = {}
for key,values in data.items():
group = grouper(results,key)
next(group)
for value in values:
group.send(value)
group.send(None)
print(results)

data = {
'girls;kg':
[40.9,38.5,42.2,45.2,41.7,44.5,38.0],
'girls:m':
[1.6,1.51,1.3,1.41,1.39,1.33,1.46],
}

if __name__ == '__main__':
main(data)

#输出结果
# {'girls;kg': Result(cunt=7, average=41.57142857142857), 'girls:m': Result(cunt=7, average=1.4285714285714286)}