import threading
import asyncio
import time

@asyncio.coroutine
def hello(n):
    print("-----")
    time.sleep(3)
    print("======")
    print(n,'Hello world! (%s)' % threading.currentThread())
    yield from asyncio.sleep(1) # 异步调用asyncio.sleep(1):  
    print(n,'Hello again! (%s)' % threading.currentThread())

loop = asyncio.get_event_loop()  # 获取EventLoop:
h1 = hello(1)
h2 = hello(2)
tasks = [h1,h2]
loop.run_until_complete(asyncio.wait(tasks)) # 执行coroutine
loop.close()

运行结果：

-----
======
2 Hello world! (<_MainThread(MainThread, started 4328)>)
-----
======
1 Hello world! (<_MainThread(MainThread, started 4328)>)
2 Hello again! (<_MainThread(MainThread, started 4328)>)
1 Hello again! (<_MainThread(MainThread, started 4328)>)

问题： 为什么 2 hello world 先被输出了？？