yield 和生成器(generator)

本文主要是介绍yield 和生成器(generator)，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

Python3

迭代器

https://www.runoob.com/python3/python3-iterator-generator.html

#!coding:utf8#author:yqq
#date:2020/1/14 0014 15:21
#description:class MyNumber:def __init__(self, init_number = 1 , bound_number = 99999):self.n  = init_numberself.bound = bound_numberdef __iter__(self):  #实现  __iter__ 方法return self def __next__(self): #实现  __next__ 方法x = self.nif x > self.bound:raise StopIterationself.n += 1return  xdef main():num_iter = MyNumber(init_number=9, bound_number=888)print(  next(num_iter)  )print(  next(num_iter)  )print(  next(num_iter)  )# for i in num_iter:#     print(i)# while True:#     print(next(num_iter))while True:try:print(next(num_iter))except StopIteration:print('over')breakexcept  Exception as e:print(f'error: {e}')passif __name__ == '__main__':main()

yield 和生成器(generator)

列表生成器

>>> [i for i in range(10)]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

生成器函数

#!coding:utf8#author:yqq
#date:2020/1/14 0014 15:29
#description:
#  对于yield的理解:
#      生成器函数遇到 yield, 立即返回, 并保存现场(保存了变量的值), 下次再次从yield后的语句执行
#    换句话说: yield保存了函数执行过程中的 "中间状态"  下次再次从"中间状态" 继续执行def my_fib(nmax = 99):""":param nmax: 最大数, 防止无限生成下去:return:"""counter  =  nmaxa , b = 0, 1yield a   # 第一个数 0yield b   # 第二个数  1for i in range(counter):yield a + ba, b = b, a + bdef main():fib_gen = my_fib()# print(next(fib_gen))# print(next(fib_gen))# print(next(fib_gen))# print(next(fib_gen))# print(next(fib_gen))for n in fib_gen:print(n)passif __name__ == '__main__':main()

基于生成器的协程

使用 @asyncio.coroutine 修饰函数

此装饰器 已弃用 并计划觉得 Python 3.10 中移除。


import asyncio@asyncio.coroutine
def old_style_coroutine():print('old_style_coroutine()')yield from asyncio.sleep(1)async def main():await old_style_coroutine()asyncio.run( main() )

async 和 await

从 Python3.7开始使用 async和await 代替 @asyncio.coroutine 和yield from

asyncio官方文档: https://docs.python.org/zh-cn/3/library/asyncio.html

https://www.cnblogs.com/dhcn/p/9032461.html

#!coding:utf8#author:yqq
#date:2020/1/14 0014 11:49
#description:import requests
import asyncio
import timeasync def test2(i):print('\n')print('------进入test2-------------')print('-------开始 await  other_test()------')r = await other_test(i)print('-------结束 await  other_test()------')print(i,r)print('----------结束test2------------------')print('\n')async def other_test(i):print('\n')print('-----------进入 other_test()-----------')print('开始 http  get 请求')r = requests.get(i)print('结束 http get请求')print(i)print('开始 休眠 4s')if 'sina' in i:await asyncio.sleep(5)  #挂起当前协程, 让出cpu给其他协程(继续事件循环)await asyncio.sleep(0.1)  #挂起当前协程, 让出cpu给其他协程(继续事件循环)# time.sleep(4)  #如果改成 time.sleep(4)  则完全是同步方式(顺序执行) 会阻塞事件循环print(f'\033[32m 结束 {i} 休眠 \033[0m')print(time.time()-start)print('--------结束other_test------------------')print('\n')return rurl = ["https://www.jd.com","https://www.sina.com","https://www.baidu.com"]print('开始创建事件循环 ')
loop = asyncio.get_event_loop()print('开始生成 task')
task = [asyncio.ensure_future(test2(i)) for i in url]start = time.time()print('开始运行事件循环')
loop.run_until_complete(asyncio.wait(task))print('\n')
print('结束运行事件循环')
endtime = time.time()-startprint(endtime)print('关闭事件循环')
loop.close()

异步echo_server

from curio import run, spawn
from curio.socket import *async def echo_server(address):sock = socket(AF_INET, SOCK_STREAM)sock.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)sock.bind(address)sock.listen(5)print('Server listening at', address)async with sock:while True:client, addr = await sock.accept()await spawn(echo_client, client, addr)async def echo_client(client, addr):print('Connection from', addr)async with client:while True:data = await client.recv(100000)if not data:breakawait client.sendall(data)print('Connection closed')if __name__ == '__main__':run(echo_server, ('',25000))