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协程类似于进程，在IO或者其他需要较长等待时间的操作执行结束前执行其他操作，但是因为不用进程切换，所以效率高。也可以用多进程加协程充分利用CPU
用作协程的生成器
from inspect import getgeneratorstate
def average():
total = 0.0
count = 0
average = None
while True:
term = yield average
total += term
count += 1
average = total / count
a = average()
next(a)
print(a.send(1))
print(a.send(3))
a.close()
预激生成器
def coroutine(function):
@wraps(function)
def call_it(*args,**kwargs):
gen = function(*args,**kwargs)
next(gen)
return gen
return call_it
@coroutine
def average():
total = 0.0
count = 0
average = None
while True:
term = yield average
total += term
count += 1
average = total / count
a = average()
print(a.send(1))
print(a.send(3))
a.close()
处理异常
from functools import wraps
def coroutine(function):
@wraps(function)
def call_it(*args,**kwargs):
gen = function(*args,**kwargs)
next(gen)
return gen
return call_it
class Demo(Exception):
pass
@coroutine
def average():
total = 0.0
count = 0
average = None
while True:
try:
term = yield average
total += term
except Exception:
print("wrong value")
else:
count += 1
average = total / count
a = average()
print(a.send(1))
print(a.send(3))
print(a.throw(Demo)) # 不会改变平均值
print(a.send("1")) # 不会改变平均值
a.close()
协程返回值
from functools import wraps
def coroutine(function):
@wraps(function)
def call_it(*args,**kwargs):
gen = function(*args,**kwargs)
next(gen)
return gen
return call_it
class Demo(Exception):
pass
@coroutine
def average():
total = 0.0
count = 0
average = None
while True:
try:
term = yield
if term is None:
break
total += term
except Exception:
print("wrong value")
else:
count += 1
average = total / count
return average
a = average()
a.send(1)
a.send(3)
try:
a.send(None)
except StopIteration as e:
print(e.value)
a.close()
asyncio 库
可以借助 asyncio 库里的函数将一个普通函数改成协程
官方文档：https://docs.python.org/3/library/asyncio.html
例子一
import asyncio
@asyncio.coroutine
def hello():
print("Hello world!")
# 异步调用asyncio.sleep(1):
r = yield from asyncio.sleep(1)
print("Hello again!")
# 获取EventLoop:
loop = asyncio.get_event_loop()
loop2 = asyncio.get_event_loop()
# 执行coroutine
loop.run_until_complete(hello())
task = []
for i in range(10):
task.append(hello())
loop2.run_until_complete(asyncio.wait(task))
loop.close()
loop2.close()
例子二
@asyncio.coroutine
def smart_fib(n):
index = 0
a = 0
b = 1
while index < n:
sleep_secs = random.uniform(0, 0.2)
yield from asyncio.sleep(sleep_secs)
print('Smart one think {} secs to get {}'.format(sleep_secs, b))
a, b = b, a + b
index += 1
@asyncio.coroutine
def stupid_fib(n):
index = 0
a = 0
b = 1
while index < n:
sleep_secs = random.uniform(0, 0.4)
yield from asyncio.sleep(sleep_secs)
print('Stupid one think {} secs to get {}'.format(sleep_secs, b))
a, b = b, a + b
index += 1
if __name__ == '__main__':
loop = asyncio.get_event_loop()
tasks = [
asyncio.async(smart_fib(10)),
asyncio.async(stupid_fib(10)),
]
loop.run_until_complete(asyncio.wait(tasks))
print('All fib finished.')
loop.close()
async 和 await 关键字
这两个字是在 Python 3.5 引入的，async 类似与 @asyncio.coroutine ，await 类似于 yield from
改写上文的例子。
async def smart_fib(n):
index = 0
a = 0
b = 1
while index < n:
sleep_secs = random.uniform(0, 0.2)
await asyncio.sleep(sleep_secs)
print('Smart one think {} secs to get {}'.format(sleep_secs, b))
a, b = b, a + b
index += 1
async def stupid_fib(n):
index = 0
a = 0
b = 1
while index < n:
sleep_secs = random.uniform(0, 0.4)
await asyncio.sleep(sleep_secs)
print('Stupid one think {} secs to get {}'.format(sleep_secs, b))
a, b = b, a + b
index += 1
if __name__ == '__main__':
loop = asyncio.get_event_loop()
tasks = [
asyncio.ensure_future(smart_fib(10)),
asyncio.ensure_future(stupid_fib(10)),
]
loop.run_until_complete(asyncio.wait(tasks))
print('All fib finished.')
loop.close()
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