Python 爬虫性能相关总结_Python

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

asyncio
gevent
Twisted
Tornado

下面分别是这四种代码的实现例子：

asyncio例子1：

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									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：

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									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：

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									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

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									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

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									#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

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									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()