爬虫效率提升方法

协程：在函数(特殊函数)定义的时候,使用async修饰,函数调用后,内部语句不会立即执行,而是会返回一个协程对象
任务对象：任务对象=高级的协程对象(进一步封装)=特殊的函数，任务对象必须要注册到时间循环对象中，给任务对象绑定回调:爬虫的数据解析中
事件循环：当做是一个装载任务对象的容器，当启动事件循环对象的时候,存储在内的任务对象会异步执行

先起个flask服务

from flask import Flask
import time

app = Flask(__name__)

@app.route('/张三')
def index_bobo():
  time.sleep(2)
  return 'hello 张三!'

@app.route('/李四')
def index_jay():
  time.sleep(2)
  return 'hello 李四!'

@app.route('/王五')
def index_tom():
  time.sleep(2)
  return 'hello 王五!'

if __name__ == '__main__':
  app.run(threaded=True)

一，aiohttp模块+单线程多任务异步协程

import asyncio
import aiohttp
import requests
import time

start = time.time()
async def get_page(url):
  # page_text = requests.get(url=url).text
  # print(page_text)
  # return page_text
  async with aiohttp.ClientSession() as s: #生成一个session对象
    async with await s.get(url=url) as response:
      page_text = await response.text()
      print(page_text)
  return page_text

urls = [
 'http://127.0.0.1:5000/张三',
  'http://127.0.0.1:5000/李四',
  'http://127.0.0.1:5000/王五',
]
tasks = []
for url in urls:
  c = get_page(url)
  task = asyncio.ensure_future(c)
  tasks.append(task)
loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.wait(tasks))

end = time.time()
print(end-start)

二，aiohttp模块实现单线程+多任务异步协程

import aiohttp
import asyncio
from lxml import etree
import time

start = time.time()
# 特殊函数:请求的发送和数据的捕获
# 注意async with await关键字
async def get_request(url):
  async with aiohttp.ClientSession() as s:
    async with await s.get(url=url) as response:
      page_text = await response.text()
      return page_text    # 返回页面源码

# 回调函数,解析数据
def parse(task):
  page_text = task.result()
  tree = etree.HTML(page_text)
  msg = "".join(tree.xpath('//text()'))
  print(msg)

urls = [
 'http://127.0.0.1:5000/张三',
  'http://127.0.0.1:5000/李四',
  'http://127.0.0.1:5000/王五',
]
tasks = []
for url in urls:
  c = get_request(url)
  task = asyncio.ensure_future(c)
  task.add_done_callback(parse) #绑定回调函数!
  tasks.append(task)
loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.wait(tasks))

end = time.time()
print(end-start)

三，requests模块+线程池

import time
import requests
from multiprocessing.dummy import Pool

start = time.time()
urls = [
 'http://127.0.0.1:5000/张三',
  'http://127.0.0.1:5000/李四',
  'http://127.0.0.1:5000/王五',
]
def get_request(url):
  page_text = requests.get(url=url).text
  print(page_text)
  return page_text

pool = Pool(3)
pool.map(get_request, urls)
end = time.time()
print('总耗时:', end-start)