说明
本文来自https://blog.csdn.net/weixin_30748995/article/details/98896747，感谢大佬演示了从生成器到协程转变的过程，希望对大家有所帮助。
定义生成器
yield关键字，可以让我们定义一个生成器函数。
def generator_func():
print('a')
yield 1
g = generator_func()
print(g)
>> > < generator object generator_func at 0x10e178b88 >
推动生成器
使用next函数从生成器中取值
def generator_func():
print('a')
yield 1
g = generator_func()
ret1 = next(g)
print(ret1)
>> >
a
1
使用next可以推动生成器的执行，下面的代码，我们可以看到每一次执行next可以让generator_func中的代码从上一个位置开始继续执行到yield，并且将yield后面的值返回到函数外部，最终我们可以执行到yield
def generator_func():
print('a')
yield 1
print('b')
yield 2
print('c')
yield 3
print('d')
g = generator_func()
ret1 = next(g)
print(ret1)
ret2 = next(g)
print(ret2)
ret3 = next(g)
print(ret3)
>> >
a
1
b
2
c
3
当函数中已经没有更多的yield时继续执行next(g)，遇到StopIteration
def generator_func():
print('a')
yield 1
print('b')
yield 2
print('c')
yield 3
print('d')
g = generator_func()
ret1 = next(g)
print(ret1)
ret2 = next(g)
print(ret2)
ret3 = next(g)
print(ret3)
next(g)
next和StopIteration
send向生成器中发送数据。send的作用相当于next，只是在驱动生成器继续执行的同时还可以向生成器中传递数据。
import numbers
def cal_sum():
sum_num = 0
while True:
num = yield
if isinstance(num, numbers.Integral):
sum_num += num
print('sum :', sum_num)
elif num is None:
break
g = cal_sum()
g.send(None) # 相当于next(g),预激活生成器
g.send(31)
g.send(25)
g.send(17)
g.send(8)
>> >
sum: 31
sum: 56
sum: 73
sum: 81
生成器中的return和StopIteration
import numbers
def cal_sum():
sum_num = 0
while True:
num = yield
if isinstance(num, numbers.Integral):
sum_num += num
print('sum :', sum_num)
elif num is None:
break
return sum_num
g = cal_sum()
g.send(None) # 相当于next(g),预激活生成器
g.send(31)
g.send(25)
g.send(17)
g.send(8)
g.send(None) # 停止生成器
>> >
sum: 31
sum: 56
sum: 73
sum: 81
Traceback(most recent call last):
File "/Users/jingliyang/PycharmProjects/python的进阶/manager.py", line 19, in < module >
g.send(None)
StopIteration: 81
import numbers
def cal_sum():
sum_num = 0
while True:
num = yield
if isinstance(num, numbers.Integral):
sum_num += num
print('sum :', sum_num)
elif num is None:
break
return sum_num
g = cal_sum()
g.send(None) # 相当于next(g),预激活生成器
g.send(31)
g.send(25)
g.send(17)
g.send(8)
try:
g.send(None) # 停止生成器
except StopIteration as e:
print(e.value)
异常处理以及获取return的值
生成器的close和throw
使用throw向生成器中抛一个异常,throw和send、next相同，都是驱动生成器继续执行，只不过throw用来向生成器中抛一个异常
def throw_test():
print('a')
yield 1
print('b')
yield 2
g = throw_test()
next(g)
g.throw(Exception, 'value error')
>> >
a Traceback(most recent call last):
File "/Users/jingliyang/PycharmProjects/python的进阶/manager.py", line 32, in < module >
g.throw(ValueError, 'value error')
File "/Users/jingliyang/PycharmProjects/python的进阶/manager.py", line 26, in throw_test
yield 1
ValueError: value
error
def throw_test():
print('a')
try:
yield 1
except ValueError:
pass
print('b')
yield 2
g = throw_test()
next(g)
ret = g.throw(ValueError, 'value error')
print(ret)
>> >
a
b
2
throw + 异常处理
使用close关闭一个生成器
def throw_test():
print('a')
yield 1
print('b')
yield 2
g = throw_test()
ret1 = next(g)
print(ret1)
g.close()
next(g)
>> >
a
1
Traceback(most recent call last):
File "/Users/jingliyang/PycharmProjects/python的进阶/manager.py", line 45, in < module >
next(g)
StopIteration
yield from关键字
yield from关键字可以直接返回一个生成器
l = ['h', 'e', 'l']
dic = {'l': 'v1', 'o': 'v2'}
s = 'eva'
def yield_from_gen():
for i in l:
yield i
for j in dic:
yield j
for k in s:
yield k
for item in yield_from_gen():
print(item, end='++')
>> > h++e++l++l++o++e++v++a++
l = ['h', 'e', 'l']
dic = {'l': 'v1', 'o': 'v2'}
s = 'eva'
def yield_from_gen():
yield from l
yield from dic
yield from s
for item in yield_from_gen():
print(item, end='++')
>> > h++e++l++l++o++e++v++a++
from itertools import chain
l = ['h', 'e', 'l']
dic = {'l': 'v1', 'o': 'v2'}
s = 'eva'
def yield_from_gen():
yield from chain(l, dic, s)
for item in yield_from_gen():
print(item, end='++')
>> > h++e++l++l++o++e++v++a++
chain和yield from
利用yield from完成股票的计算，yield from能够完成一个委派生成器的作用，在子生成器和调用者之间建立起一个双向通道。
from itertools import chain
l = ['h', 'e', 'l']
dic = {'l': 'v1', 'o': 'v2'}
s = 'eva'
def yield_from_gen():
yield from chain(l, dic, s)
for item in yield_from_gen():
print(item, end='++')
"""
0 -
6.4 -
6.45 -
6.5 -
6.425 -
6.359999999999999 -
6.3999999999999995 -
6.442857142857143 -
sogou 6.442857142857143
0 -
0 -
181.72 -
183.15 -
183.28 -
182.46 -
163.568 -
164.62 -
166.5614285714286 -
169.40625 -
alibaba 169.40625
0 -
0 -
59.7 -
56.150000000000006 -
53.166666666666664 -
53.725 -
55.120000000000005 -
56.95000000000001 -
59.38571428571429 -
美团 59.38571428571429
0 -
(test2) C:\Users\asinall4\PycharmProjects\test2>python 083.py
0 -
6.4 -
6.45 -
6.5 -
6.425 -
6.359999999999999 -
6.3999999999999995 -
6.442857142857143 -
++++++++++++++++++++++++++++++++++++++++++++++++++
sogou 6.442857142857143
0 -
0 -
181.72 -
183.15 -
183.28 -
182.46 -
163.568 -
164.62 -
166.5614285714286 -
169.40625 -
++++++++++++++++++++++++++++++++++++++++++++++++++
alibaba 169.40625
0 -
0 -
59.7 -
56.150000000000006 -
53.166666666666664 -
53.725 -
55.120000000000005 -
56.95000000000001 -
59.38571428571429 -
++++++++++++++++++++++++++++++++++++++++++++++++++
美团 59.38571428571429
0 -
"""
协程
概念:根据维基百科给出的定义，“协程是为非抢占式多任务产生子程序的计算机程序组件，协程允许不同入口点在不同位置暂停或开始执行程序”。从技术的角度来说，“协程就是你可以暂停执行的函数”。如果你把它理解成“就像生成器一样”，那么你就想对了。
使用yield实现协程
import time
def consumer():
'''任务1:接收数据,处理数据'''
while True:
x = yield
def producer():
'''任务2:生产数据'''
g = consumer()
next(g)
for i in range(10000000):
g.send(i)
producer()
使用yield from实现的协程
import datetime
import heapq
import types
import time
class Task:
def __init__(self, wait_until, coro):
self.coro = coro
self.waiting_until = wait_until
def __eq__(self, other):
return self.waiting_until == other.waiting_until
def __lt__(self, other):
return self.waiting_until < other.waiting_until
class SleepingLoop:
def __init__(self, *coros):
self._new = coros
self._waiting = []
def run_until_complete(self):
for coro in self._new:
wait_for = coro.send(None)
heapq.heappush(self._waiting, Task(wait_for, coro))
while self._waiting:
now = datetime.datetime.now()
task = heapq.heappop(self._waiting)
if now < task.waiting_until:
delta = task.waiting_until - now
time.sleep(delta.total_seconds())
now = datetime.datetime.now()
try:
print('*' * 50)
wait_until = task.coro.send(now)
print('-' * 50)
heapq.heappush(self._waiting, Task(wait_until, task.coro))
except StopIteration:
pass
def sleep(seconds):
now = datetime.datetime.now()
wait_until = now + datetime.timedelta(seconds=seconds)
print('before yield wait_until')
actual = yield wait_until # 返回一个datetime数据类型的时间
print('after yield wait_until')
return actual - now
def countdown(label, length, *, delay=0):
print(label, 'waiting', delay, 'seconds before starting countdown')
delta = yield from sleep(delay)
print(label, 'starting after waiting', delta)
while length:
print(label, 'T-minus', length)
waited = yield from sleep(1)
length -= 1
print(label, 'lift-off!')
def main():
loop = SleepingLoop(countdown('A', 5), countdown('B', 3, delay=2),
countdown('C', 4, delay=1))
start = datetime.datetime.now()
loop.run_until_complete()
print('Total elapsed time is', datetime.datetime.now() - start)
if __name__ == '__main__':
main()
await和async关键字
使用async function可以定义一个异步函数，在async关键字定义的函数中不能出现yield和yield from
例1
async def download(url): # 加入新的关键字 async ，可以将任何一个普通函数变成协程
return 'eva'
ret = download('http://www.baidu.com/')
print(ret) # <coroutine object download at 0x108b3a5c8>
ret.send(None) # StopIteration: eva
例2
async def download(url):
return 'eva'
def run(coroutine):
try:
coroutine.send(None)
except StopIteration as e:
return e.value
coro = download('http://www.baidu.com/')
ret = run(coro)
print(ret) # eva
async关键字不能和yield一起使用，引入coroutine装饰器来装饰downloader生成器。
await操作符后面必须跟一个awaitable对象（通常用于等待一个会有io操作的任务）, 它只能在异步函数async function内部使用。
例3
import types
@types.coroutine # 将一个生成器变成一个awaitable的对象
def downloader(url):
yield 'aaa'
async def download_url(url): # 协程
waitable = downloader(url)
print(waitable) # <generator object downloader at 0x1091e2c78> 生成器
html = await waitable
return html
coro = download_url('http://www.baidu.com')
print(coro) # <coroutine object download_url at 0x1091c9d48>
ret = coro.send(None)
print(ret)
asyncio模块
asyncio是Python3.4版本引入的标准库，直接内置了对异步IO的支持。asyncio的编程模型就是一个消息循环。我们从asyncio模块中直接获取一个EventLoop的引用，然后把需要执行的协程扔到EventLoop中执行，就实现了异步IO。
coroutine + from
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()
# 执行coroutine
loop.run_until_complete(hello())
loop.close()
async + await
import asyncio
async def hello():
print("Hello world!")
# 异步调用asyncio.sleep(1):
r = await asyncio.sleep(1)
print("Hello again!")
# 获取EventLoop:
loop = asyncio.get_event_loop()
# 执行coroutine
loop.run_until_complete(hello())
loop.close()
执行多个任务
import asyncio
async def hello():
print("Hello world!")
await asyncio.sleep(1)
print("Hello again!")
return 'done'
loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.wait([hello(), hello()]))
loop.close()
获取返回值
import asyncio
async def hello():
print("Hello world!")
await asyncio.sleep(1)
print("Hello again!")
return 'done'
loop = asyncio.get_event_loop()
task = loop.create_task(hello())
loop.run_until_complete(task)
ret = task.result()
print(ret)
执行多个任务获取返回值
import asyncio
async def hello(i):
print("Hello world!")
await asyncio.sleep(i)
print("Hello again!")
return 'done', i
loop = asyncio.get_event_loop()
task1 = loop.create_task(hello(2))
task2 = loop.create_task(hello(1))
task_l = [task1, task2]
tasks = asyncio.wait(task_l)
loop.run_until_complete(tasks)
for t in task_l:
print(t.result())
执行多个任务按照返回的顺序获取返回值
import asyncio
async def hello(i):
print("Hello world!")
await asyncio.sleep(i)
print("Hello again!")
return 'done', i
async def main():
tasks = []
for i in range(20):
tasks.append(asyncio.ensure_future(hello((20 - i) / 10)))
for res in asyncio.as_completed(tasks):
result = await res
print(result)
loop = asyncio.get_event_loop()
loop.run_until_complete(main())
asyncio使用协程完成http访问
import asyncio
async def get_url():
reader, writer = await asyncio.open_connection('www.baidu.com', 80)
writer.write(b'GET / HTTP/1.1\r\nHOST:www.baidu.com\r\nConnection:close\r\n\r\n')
all_lines = []
async for line in reader:
data = line.decode()
all_lines.append(data)
html = '\n'.join(all_lines)
return html
async def main():
tasks = []
for url in range(20):
tasks.append(asyncio.ensure_future(get_url()))
for res in asyncio.as_completed(tasks):
result = await res
print(result)
if __name__ == '__main__':
loop = asyncio.get_event_loop()
loop.run_until_complete(main()) # 处理一个任务
loop.run_until_complete(asyncio.wait([main()])) # 处理多个任务
task = loop.create_task(main()) # 使用create_task获取返回值
loop.run_until_complete(task)
loop.run_until_complete(asyncio.wait([task]))
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