初识Python-Asyncio

yield

yield能将一个函数转换成 generator(生成器)，它只能通过调用next()/send()才开始执行，执行到每一个yield语句就会中断，交出执行权，并返回一个迭代值，下次执行从yield中断处可以通过send()接收一个参数并继续执行。
send与next的不同是send可以传值到yield语句的左边。例如

def test():
    ...
    arg = yield n

使用test().send(1)时，test函数会将此时的n返回且将1赋值给arg
但是注意在第一次调用test函数时如果使用test().send(1)会报错，因为第一次调用时应将函数中断在yield语句处，即使用test().next()或者是test.send(None)

next

eg.1

import asyncio

def test():
    yield 1
    yield 2

if __name__=='__main__':
    func = test()
    print(next(func))
    print(next(func))

1
2

eg.2

import asyncio

def test():
    arg = yield 1
    yield arg

if __name__=='__main__':
    func = test()
    print(next(func))
    print(next(func))

1
None

send

eg.1

import asyncio

def test():
    arg = yield 1
    yield arg

if __name__=='__main__':
    func = test()
    print(func.send(None))
    print(func.send(100))

1
100

eg.2

import asyncio

def test():
    yield 1
    yield 2

if __name__=='__main__':
    func = test()
    print(func.send(None))
    print(func.send(100))

1
2

eg.3

import asyncio

def test():
    yield 1
    yield 2

if __name__=='__main__':
    func = test()
    print(func.send(50))
    print(func.send(100))

Traceback (most recent call last):
  File "d:\cheng.dongquan\Working\Ocpp\test.py", line 9, in <module>
    print(func.send(2))
TypeError: can't send non-None value to a just-started generator

yield from

目前就只给一个简单的案例。
在下面他相当于时一个中间件：

import asyncio

def test():
    yield 1
    yield 2
def main():
    yield from test()
if __name__=='__main__':
    func = main()
    print(next(func))
    print(next(func))

1
2

asyncio

参考廖雪峰的官方网站 ## async/await

import threading
import asyncio

async def hello():
    print('Hello world! (%s)' % threading.currentThread())
    await asyncio.sleep(1)
    print('Hello again! (%s)' % threading.currentThread())

loop = asyncio.get_event_loop()
tasks = [hello(), hello()]
loop.run_until_complete(asyncio.wait(tasks))
loop.close()

Hello world! (<_MainThread(MainThread, started 140735195337472)>)
Hello world! (<_MainThread(MainThread, started 140735195337472)>)
(暂停约1秒)
Hello again! (<_MainThread(MainThread, started 140735195337472)>)
Hello again! (<_MainThread(MainThread, started 140735195337472)>)

aiohttp

pass