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Python 爬虫性能相关总结

程序员文章站 2022-03-07 18:14:43
这里我们通过请求网页例子来一步步理解爬虫性能当我们有一个列表存放了一些url需要我们获取相关数据,我们首先想到的是循环简单的循环串行这一种方法相对来说是最慢的,因为一个一个循环,耗时是最长的,是所有的...

这里我们通过请求网页例子来一步步理解爬虫性能

当我们有一个列表存放了一些url需要我们获取相关数据,我们首先想到的是循环

简单的循环串行

这一种方法相对来说是最慢的,因为一个一个循环,耗时是最长的,是所有的时间总和
代码如下:

import requests

url_list = [
  'http://www.baidu.com',
  'http://www.pythonsite.com',
  'http://www.cnblogs.com/'
]

for url in url_list:
  result = requests.get(url)
  print(result.text)

通过线程池

通过线程池的方式访问,这样整体的耗时是所有连接里耗时最久的那个,相对循环来说快了很多

import requests
from concurrent.futures import threadpoolexecutor

def fetch_request(url):
  result = requests.get(url)
  print(result.text)

url_list = [
  'http://www.baidu.com',
  'http://www.bing.com',
  'http://www.cnblogs.com/'
]
pool = threadpoolexecutor(10)

for url in url_list:
  #去线程池中获取一个线程,线程去执行fetch_request方法
  pool.submit(fetch_request,url)

pool.shutdown(true)

线程池+回调函数

这里定义了一个回调函数callback

from concurrent.futures import threadpoolexecutor
import requests


def fetch_async(url):
  response = requests.get(url)

  return response


def callback(future):
  print(future.result().text)


url_list = [
  'http://www.baidu.com',
  'http://www.bing.com',
  'http://www.cnblogs.com/'
]

pool = threadpoolexecutor(5)

for url in url_list:
  v = pool.submit(fetch_async,url)
  #这里调用回调函数
  v.add_done_callback(callback)

pool.shutdown()

通过进程池

通过进程池的方式访问,同样的也是取决于耗时最长的,但是相对于线程来说,进程需要耗费更多的资源,同时这里是访问url时io操作,所以这里线程池比进程池更好

import requests
from concurrent.futures import processpoolexecutor

def fetch_request(url):
  result = requests.get(url)
  print(result.text)

url_list = [
  'http://www.baidu.com',
  'http://www.bing.com',
  'http://www.cnblogs.com/'
]
pool = processpoolexecutor(10)

for url in url_list:
  #去进程池中获取一个线程,子进程程去执行fetch_request方法
  pool.submit(fetch_request,url)

pool.shutdown(true)

进程池+回调函数

这种方式和线程+回调函数的效果是一样的,相对来说开进程比开线程浪费资源

from concurrent.futures import processpoolexecutor
import requests


def fetch_async(url):
  response = requests.get(url)

  return response


def callback(future):
  print(future.result().text)


url_list = [
  'http://www.baidu.com',
  'http://www.bing.com',
  'http://www.cnblogs.com/'
]

pool = processpoolexecutor(5)

for url in url_list:
  v = pool.submit(fetch_async, url)
  # 这里调用回调函数
  v.add_done_callback(callback)

pool.shutdown()

主流的单线程实现并发的几种方式

  1. asyncio
  2. gevent
  3. twisted
  4. tornado

下面分别是这四种代码的实现例子:

asyncio例子1:

import asyncio


@asyncio.coroutine #通过这个装饰器装饰
def func1():
  print('before...func1......')
  # 这里必须用yield from,并且这里必须是asyncio.sleep不能是time.sleep
  yield from asyncio.sleep(2)
  print('end...func1......')


tasks = [func1(), func1()]

loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.gather(*tasks))
loop.close()

上述的效果是同时会打印两个before的内容,然后等待2秒打印end内容
这里asyncio并没有提供我们发送http请求的方法,但是我们可以在yield from这里构造http请求的方法。

asyncio例子2:

import asyncio


@asyncio.coroutine
def fetch_async(host, url='/'):
  print("----",host, url)
  reader, writer = yield from asyncio.open_connection(host, 80)

  #构造请求头内容
  request_header_content = """get %s http/1.0\r\nhost: %s\r\n\r\n""" % (url, host,)
  request_header_content = bytes(request_header_content, encoding='utf-8')
  #发送请求
  writer.write(request_header_content)
  yield from writer.drain()
  text = yield from reader.read()
  print(host, url, text)
  writer.close()

tasks = [
  fetch_async('www.cnblogs.com', '/zhaof/'),
  fetch_async('dig.chouti.com', '/pic/show?nid=4073644713430508&lid=10273091')
]

loop = asyncio.get_event_loop()
results = loop.run_until_complete(asyncio.gather(*tasks))
loop.close()

asyncio + aiohttp 代码例子:

import aiohttp
import asyncio


@asyncio.coroutine
def fetch_async(url):
  print(url)
  response = yield from aiohttp.request('get', url)
  print(url, response)
  response.close()


tasks = [fetch_async('http://baidu.com/'), fetch_async('http://www.chouti.com/')]

event_loop = asyncio.get_event_loop()
results = event_loop.run_until_complete(asyncio.gather(*tasks))
event_loop.close()

asyncio+requests代码例子

import asyncio
import requests


@asyncio.coroutine
def fetch_async(func, *args):
  loop = asyncio.get_event_loop()
  future = loop.run_in_executor(none, func, *args)
  response = yield from future
  print(response.url, response.content)


tasks = [
  fetch_async(requests.get, 'http://www.cnblogs.com/wupeiqi/'),
  fetch_async(requests.get, 'http://dig.chouti.com/pic/show?nid=4073644713430508&lid=10273091')
]

loop = asyncio.get_event_loop()
results = loop.run_until_complete(asyncio.gather(*tasks))
loop.close()

gevent+requests代码例子

import gevent

import requests
from gevent import monkey

monkey.patch_all()


def fetch_async(method, url, req_kwargs):
  print(method, url, req_kwargs)
  response = requests.request(method=method, url=url, **req_kwargs)
  print(response.url, response.content)

# ##### 发送请求 #####
gevent.joinall([
  gevent.spawn(fetch_async, method='get', url='https://www.python.org/', req_kwargs={}),
  gevent.spawn(fetch_async, method='get', url='https://www.yahoo.com/', req_kwargs={}),
  gevent.spawn(fetch_async, method='get', url='https://github.com/', req_kwargs={}),
])

# ##### 发送请求(协程池控制最大协程数量) #####
# from gevent.pool import pool
# pool = pool(none)
# gevent.joinall([
#   pool.spawn(fetch_async, method='get', url='https://www.python.org/', req_kwargs={}),
#   pool.spawn(fetch_async, method='get', url='https://www.yahoo.com/', req_kwargs={}),
#   pool.spawn(fetch_async, method='get', url='https://www.github.com/', req_kwargs={}),
# ])

grequests代码例子
这个是讲requests+gevent进行了封装

import grequests


request_list = [
  grequests.get('http://httpbin.org/delay/1', timeout=0.001),
  grequests.get('http://fakedomain/'),
  grequests.get('http://httpbin.org/status/500')
]


# ##### 执行并获取响应列表 #####
# response_list = grequests.map(request_list)
# print(response_list)


# ##### 执行并获取响应列表(处理异常) #####
# def exception_handler(request, exception):
# print(request,exception)
#   print("request failed")

# response_list = grequests.map(request_list, exception_handler=exception_handler)
# print(response_list)

twisted代码例子

#getpage相当于requets模块,defer特殊的返回值,rector是做事件循环
from twisted.web.client import getpage, defer
from twisted.internet import reactor

def all_done(arg):
  reactor.stop()

def callback(contents):
  print(contents)

deferred_list = []

url_list = ['http://www.bing.com', 'http://www.baidu.com', ]
for url in url_list:
  deferred = getpage(bytes(url, encoding='utf8'))
  deferred.addcallback(callback)
  deferred_list.append(deferred)
#这里就是进就行一种检测,判断所有的请求知否执行完毕
dlist = defer.deferredlist(deferred_list)
dlist.addboth(all_done)

reactor.run()

tornado代码例子

from tornado.httpclient import asynchttpclient
from tornado.httpclient import httprequest
from tornado import ioloop


def handle_response(response):
  """
  处理返回值内容(需要维护计数器,来停止io循环),调用 ioloop.ioloop.current().stop()
  :param response: 
  :return: 
  """
  if response.error:
    print("error:", response.error)
  else:
    print(response.body)


def func():
  url_list = [
    'http://www.baidu.com',
    'http://www.bing.com',
  ]
  for url in url_list:
    print(url)
    http_client = asynchttpclient()
    http_client.fetch(httprequest(url), handle_response)


ioloop.ioloop.current().add_callback(func)
ioloop.ioloop.current().start()

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