协程

协程的好处：当进程有耗时操作时，通过协程可以完成后续操作。协程切换任务资源很小，效率高。

使用yield完成多任务：

import time


def work1():
    while True:
        print("--- 1 ---")
        time.sleep(0.1)
        yield


def work2():
    while True:
        print("--- 2 ---")
        time.sleep(0.1)
        yield


def main():
    t1 = work1()
    t2 = work2()
    # 先让t1运行一会，当t1遇到yield的时候，再返回到25行，然后执行t2
    # 当t2遇到yield的时候，再返回26行，循环后回到25行，切换到t1中
    # 这样t1/t2/t1/t2的交替运行，最终实现了多任务 —— 协程
    while True:
        next(t1)
        next(t2)


if __name__ == '__main__':
    main()

　　运行结果：

--- 1 ---
--- 2 ---
--- 1 ---
--- 2 ---
--- 1 ---
--- 2 ---
--- 1 ---
--- 2 ---
--- 1 ---
--- 2 ---
......

使用greenlet完成多任务：

from greenlet import greenlet
import time


def work1():
    while True:
        print("--- 1 ---")
        gr2.switch()
        time.sleep(0.5)


def work2():
    while True:
        print("--- 2 ---")
        gr1.switch()
        time.sleep(0.5)


gr1 = greenlet(work1)
gr2 = greenlet(work2)

# 切换到gr1中运行
gr1.switch()

　　运行结果：

--- 1 ---
--- 2 ---
--- 1 ---
--- 2 ---
--- 1 ---
--- 2 ---
......

使用gevent完成多任务：

import gevent
from gevent import monkey
import time

# 有耗时操作时需要写
monkey.patch_all()    # 将程序中用到的耗时操作的代码，换为gevent中自己实现的模块


def f(n):
    for i in range(n):
        print(gevent.getcurrent(), i)
        # 程序中的耗时操作的代码，用monkey.patch_all()可以将延迟转换程gevent自己实现的模块
        # 等同gevent.sleep(0.5)
        time.sleep(0.5)
        # gevent.sleep(0.5)


# 平时使用常用joinall
gevent.joinall([gevent.spawn(f, 5), gevent.spawn(f, 5), gevent.spawn(f, 5)])
# print("测试代码1")
# g1 = gevent.spawn(f, 5)
# print("测试代码2")
# g2 = gevent.spawn(f, 5)
# print("测试代码3")
# g3 = gevent.spawn(f, 5)
# print("测试代码4")
# g1.join()
# print("测试代码5")
# g2.join()
# print("测试代码6")
# g3.join()
# 使用测试代码得知：gevent.spawn创建的对象只有在遇到耗时操作时才会执行传入的函数的代码
# 函数的代码执行完了后，再执行耗时操作后面的代码

　　运行结果：

<Greenlet at 0x34e7150: f(5)> 0
<Greenlet at 0x34e7260: f(5)> 0
<Greenlet at 0x34e7370: f(5)> 0
<Greenlet at 0x34e7150: f(5)> 1
<Greenlet at 0x34e7260: f(5)> 1
<Greenlet at 0x34e7370: f(5)> 1
<Greenlet at 0x34e7150: f(5)> 2
<Greenlet at 0x34e7260: f(5)> 2
<Greenlet at 0x34e7370: f(5)> 2
<Greenlet at 0x34e7150: f(5)> 3
<Greenlet at 0x34e7260: f(5)> 3
<Greenlet at 0x34e7370: f(5)> 3
<Greenlet at 0x34e7150: f(5)> 4
<Greenlet at 0x34e7260: f(5)> 4
<Greenlet at 0x34e7370: f(5)> 4

案例：使用gevent多任务爬取图片：

import requests
import re
import os
import gevent
from gevent import monkey

monkey.patch_all()

headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3729.169 Safari/537.36'}
response = requests.get('https://www.qqtn.com/article/article_277732_1.html', headers=headers)
# print(response)
html = response.text
dir_name = ['美女微信背景图'][0]
os.mkdir(dir_name)

urls = re.findall('<p align="center"><img src="(.*?)"/></p>', html)
print(urls)


def download(img_name, img_url):
    req = requests.get(img_url)
    img_content = req.content
    with open(dir_name + '/' + img_name, 'wb') as f:
        f.write(img_content)


def main():
    i = 0
    while i < len(urls):
        name = str(i)+'.jpg'
        gevent.joinall([
            gevent.spawn(download, name, urls[i])
        ])
        i += 1


if __name__ == '__main__':
    main()