asyncio是Python 3.4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。

asyncio实现了TCP、UDP、SSL等协议，aiohttp则是基于asyncio实现的HTTP框架。
我们先安装aiohttp：

pip install aiohttp

aiomysql 异步操作使用mysql需要用到aiomysql

pip install aiomysql

pyquery是用来读取html的工具

 pip install pyquery

全部具体代码如下:

import re
import asyncio
import aiohttp
import aiomysql
from pyquery import PyQuery
sem = asyncio.Semaphore(3) # 3个允许的同时请求的数量
start_url = 'http://jobbole.com/'
stopping = False
waitting_urls = [] # 等待中的文章
seen_urls = set()   # 爬取过的文章


async def fetch(url,session):
    """爬取对应url里的内容"""
    async with sem:
        await asyncio.sleep(1)
        try:
            async with session.get(url) as resp:
                print("url status: {}".format(resp.status))
                if resp.status in [200, 201]:
                    data = await resp.text()
                    return data
        except Exception as e:
            print(e)


async def init_urls(url, session):
    """没匹配到正则则, 接着爬"""
    html = await fetch(url, session)
    seen_urls.add(url)
    extract_urls(html)


async def article_handler(url, session, pool):
    """获取文章并解析入库"""
    html = await fetch(url, session)
    seen_urls.add(url)
    extract_urls(html)
    pq = PyQuery(html)
    title = pq("title").text()
    async with pool.get() as conn:
        async with conn.cursor() as cur:
            await cur.execute("SELECT 42;")
            insert_sql = "insert into article_test(title) values('{}')".format(title)
            await cur.execute(insert_sql)


async def consumer(pool):
    """不断的从等待列表爬取文章"""
    async with aiohttp.ClientSession() as session:
        while not stopping:
            if len(waitting_urls) ==0:
                await asyncio.sleep(0.5)
                continue

            url = waitting_urls.pop()
            print("start get url: {}".format(url))
            if re.match('http://.*?jobbole.com/\d+/', url):
                if url not in seen_urls:
                    asyncio.ensure_future(article_handler(url, session, pool))
            else:
                if url not in seen_urls:
                    asyncio.ensure_future(init_urls(url, session))


def extract_urls(html):
    """解析html, 从href提取url放入到等待中的url"""
    urls = []
    pq = PyQuery(html)
    for link in pq.items("a"):
        url = link.attr("href")
        if url and url.startswith("http") and url not in seen_urls:
            urls.append(url)
            waitting_urls.append(url)


async def main(loop):
    # mysql准备
    pool = await aiomysql.create_pool(host='localhost', port=3306,
                           user='root', password='123456',
                           db='aiomysql', loop = loop, charset="utf8", autocommit=True)
    async with aiohttp.ClientSession() as session:
        html = await fetch(start_url, session)
        seen_urls.add(start_url)
        extract_urls(html)
    asyncio.ensure_future(consumer(pool))


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    asyncio.ensure_future(main(loop))
    loop.run_forever()

解析

if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    asyncio.ensure_future(main(loop))
    loop.run_forever()

asyncio.get_event_loop()将创建一个事件循环, asyncio.ensure_future将创建一个任务, 参数是一个协程, loop.run_forever()会一直运行, 直到被stop停止

async def main(loop):
    # mysql准备
    pool = await aiomysql.create_pool(host='localhost', port=3306,
                           user='root', password='123456',
                           db='aiomysql', loop = loop, charset="utf8", autocommit=True)
    # fetch() 用于解析html内容, extract_urls用于解析html中的a标签里的url,并放入等待列表
    async with aiohttp.ClientSession() as session:
        html = await fetch(start_url, session)
        seen_urls.add(start_url)
        extract_urls(html)
    asyncio.ensure_future(consumer(pool))

async标记一个方法标记为协程, 然后在协程内部用await 调用另一个协程实现异步操作。