# 生成器表达式
a = (x*x for x in range(10))
# next生成值
next(a()) # 输出0
next(a()) # 输出1
next(a()) # 输出4

 def writer():
  print('-> coroutine started')
  for i in range(8):
    w = yield
    print(i+w)

w = writer()
# 本质还是生成器
> w
<generator object writer at 0x000002595BC57468>
# 首先要用next()把协程激活
> next(w)
-> coroutine started
# 发送数据
> w.send(1)
1
# send到第八次之后会抛出异常
# 因为协程已经结束了
---------------------------------------------------------------------------
StopIteration               Traceback (most recent call last)

def writer():
  while True:
    w = yield
    print('', w)

def writer_wrapper(coro):
  # 激活
  next(coro)
  while True:
    # 异常处理
    try:
      x = yield
      # 发送数据给writer
      coro.send(x)
    except StopIteration:
      pass
w = writer()
wrap = writer_wrapper(w)
# 激活
next(wrap)
for i in range(4):
  wrap.send(i)
# 输出
 0
 1
 2
 3

def writer():
  while True:
    w = yield
    print('', w)
def writer_wrapper2(coro):
  yield from coro

async def func():
  await 'some code'