requests作为scrapy下载中间件

转载

误会一场 2024-10-12 14:50:17

文章标签 中间件 python ide Android 文章分类 架构后端开发

scrapy中间件：

scrapy中间件介绍
下载器中间件

添加ip代理
UA中间件
cookies中间件

爬虫中间件

核心方法

scrapy中间件介绍

=
scrapy中间件是scrapy框架的重要组成部分
分为两大种类：下载器中间件（DownloaderMiddleware）和爬虫中间件（SpiderMiddleware）
图中4、5为下载器中间件
图中6、7为爬虫中间件

requests作为scrapy下载中间件_Android

下载器中间件是Scrapy请求/响应处理的钩子框架。这是一个轻，低层次的系统，全球范围内改变斯拉皮的请求和响应。

下载器中间件主要功能：
1、添加ip代理
2、添加cookie
3、添加UA
4、请求重试

Spider中间件是一个钩子框架，可以钩住Scrapy的Spider处理机制，在该机制中，您可以插入自定义功能来处理发送到的响应。蜘蛛用于处理和处理由spider生成的请求和项目。

爬虫中间件主要功能：
1、处理引擎传递给爬虫的响应
2、处理爬虫传递给引擎的请求
3、处理爬虫传递给引擎的数据项

其中，爬虫中间件在以下情况中会被调用：

1.当运行到 yield scrapy.Request()或者 yield item 的时候，爬虫中间件的
2.process_spider_output()方法被调用。当爬虫本身的代码出现了 Exception 的时候，爬虫中间件的
3.process_spider_exception()方法被调用。当爬虫里面的某一个回调函数 parse_xxx()被调用之前，爬虫中间件的
4. process_spider_input()方法被调用。当运行到 start_requests()的时候，爬虫中间件的
5. process_start_requests()方法被调用。

=
首先，先创建一个spider用于学习middleware
打开其中的middlewares.py
初始化样子：

# Define here the models for your spider middleware
#
# See documentation in:
# https://docs.scrapy.org/en/latest/topics/spider-middleware.html

from scrapy import signals

# useful for handling different item types with a single interface
from itemadapter import is_item, ItemAdapter


class MiddlewareproSpiderMiddleware:
    # Not all methods need to be defined. If a method is not defined,
    # scrapy acts as if the spider middleware does not modify the
    # passed objects.

    @classmethod
    def from_crawler(cls, crawler):
        # This method is used by Scrapy to create your spiders.
        s = cls()
        crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
        return s

    def process_spider_input(self, response, spider):
        # Called for each response that goes through the spider
        # middleware and into the spider.

        # Should return None or raise an exception.
        return None

    def process_spider_output(self, response, result, spider):
        # Called with the results returned from the Spider, after
        # it has processed the response.

        # Must return an iterable of Request, or item objects.
        for i in result:
            yield i

    def process_spider_exception(self, response, exception, spider):
        # Called when a spider or process_spider_input() method
        # (from other spider middleware) raises an exception.

        # Should return either None or an iterable of Request or item objects.
        pass

    def process_start_requests(self, start_requests, spider):
        # Called with the start requests of the spider, and works
        # similarly to the process_spider_output() method, except
        # that it doesn’t have a response associated.

        # Must return only requests (not items).
        for r in start_requests:
            yield r

    def spider_opened(self, spider):
        spider.logger.info('Spider opened: %s' % spider.name)


class MiddlewareproDownloaderMiddleware:
    # Not all methods need to be defined. If a method is not defined,
    # scrapy acts as if the downloader middleware does not modify the
    # passed objects.

    @classmethod
    def from_crawler(cls, crawler):
        # This method is used by Scrapy to create your spiders.
        s = cls()
        crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
        return s

    def process_request(self, request, spider):
        # Called for each request that goes through the downloader
        # middleware.

        # Must either:
        # - return None: continue processing this request
        # - or return a Response object
        # - or return a Request object
        # - or raise IgnoreRequest: process_exception() methods of
        #   installed downloader middleware will be called
        return None

    def process_response(self, request, response, spider):
        # Called with the response returned from the downloader.

        # Must either;
        # - return a Response object
        # - return a Request object
        # - or raise IgnoreRequest
        return response

    def process_exception(self, request, exception, spider):
        # Called when a download handler or a process_request()
        # (from other downloader middleware) raises an exception.

        # Must either:
        # - return None: continue processing this exception
        # - return a Response object: stops process_exception() chain
        # - return a Request object: stops process_exception() chain
        pass

    def spider_opened(self, spider):
        spider.logger.info('Spider opened: %s' % spider.name)

可以看到分为两类：

class MiddlewareproDownloaderMiddleware:

class MiddlewareproSpiderMiddleware:

以下依次介绍

下载器中间件

添加ip代理

测试ip地址可访问网站 http://httpbin.org/ip 方法一：
不用中间件。重写start_ requests方法，在发送请求时传入ip—proxy

yield scrapy.Request(self.start_urls[0], meta={"proxy": proxy})

方法二：
使用中间件。

第一种：静态ip中间件
test：

import scrapy


class MiddlewaretestSpider(scrapy.Spider):
    name = 'middlewareTest'
    # allowed_domains = ['http://httpbin.org/ip']
    start_urls = ['http://httpbin.org/ip']

    def parse(self, response):
        print('IP地址--> ', response.text)

在middlewares中重写编写一个类：

class TestProxyMiddleware(object):
    def process_request(self, request, spider):
        proxy = "http://113.57.26.117"
        request.meta["proxy"] = proxy

在settings中打开;

DOWNLOADER_MIDDLEWARES = {
   # 'middlewarePro.middlewares.MiddlewareproDownloaderMiddleware': 543,
    'middlewarePro.middlewares.TestProxyMiddleware':543,

}

结果：

IP地址-->  {
  "origin": "113.57.26.117"
}

第二种：动态ip
动态ip的创建和静态ip创建原理相似，只是每次给request的meta赋予不同的proxy参数，这就要依靠代理池俩实现。
代理池就是有很多ip组成的字典，每次随机抽取一个ip，如果这个代理池足够大，就可以降低重复的概率
test不变
middlewares：
先导入两个类：

import random
from scrapy.utils.project import get_project_settings

class TestProxyMiddleware(object):

    def __init__(self):

        self.settings = get_project_settings()

    def process_request(self, request, spider):

        proxy = random.choice(self.settings['PROXIES'])
        request.meta["proxy"] = proxy

settings中接入一个代理池：

PROXIES = [
    'http://114.217.243.25:8118',
    'http://125.37.175.233:8118',
    'http://1.85.116.218:8118'
]

UA中间件

UA中间件的设置和代理的设置基本相同
middlewares中新建一个类UAMiddleware

class UAMiddleware(object):
 
    def process_request(self, request, spider):
        ua = random.choice(settings['USER_AGENT_LIST'])
        request.headers['User-Agent'] = ua

在settings中添加一个含UA数据的字典即可。

USER_AGENT_LIST = [
"Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.101 Safari/537.36",
  "Dalvik/1.6.0 (Linux; U; Android 4.2.1; 2013022 MIUI/JHACNBL30.0)",
  "Mozilla/5.0 (Linux; U; Android 4.4.2; zh-cn; HUAWEI MT7-TL00 Build/HuaweiMT7-TL00) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1",
  "AndroidDownloadManager",
  "Apache-HttpClient/UNAVAILABLE (java 1.4)",
  "Dalvik/1.6.0 (Linux; U; Android 4.3; SM-N7508V Build/JLS36C)",
  "Android50-AndroidPhone-8000-76-0-Statistics-wifi",
  "Dalvik/1.6.0 (Linux; U; Android 4.4.4; MI 3 MIUI/V7.2.1.0.KXCCNDA)",
  "Dalvik/1.6.0 (Linux; U; Android 4.4.2; Lenovo A3800-d Build/LenovoA3800-d)",
  "Lite 1.0 ( http://litesuits.com )",
  "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET4.0C; .NET4.0E; .NET CLR 2.0.50727)",
  "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/38.0.2125.122 Safari/537.36 SE 2.X MetaSr 1.0",
  "Mozilla/5.0 (Linux; U; Android 4.1.1; zh-cn; HTC T528t Build/JRO03H) AppleWebKit/534.30 (KHTML, like Gecko) Version/4.0 Mobile Safari/534.30; 360browser(securitypay,securityinstalled); 360(android,uppayplugin); 360 Aphone Browser (2.0.4)",
]

记得在settings中开启该通道;

DOWNLOADER_MIDDLEWARES = {
   # 'middlewarePro.middlewares.MiddlewareproDownloaderMiddleware': 543,
    'middlewarePro.middlewares.TestProxyMiddleware':543,
	'middlewarePro.middlewares.UAMiddleware' : 544,
}

cookies中间件

cookies值主要用于爬取一些需要登录的网站，保持登录状态。
设置cookies中间件首先要有若干cookies值，获取cookies可以用selenium登录要爬取的网址，然后下载cookies，多重复几遍就可得到多个cookies值

具体操作和上述类似

爬虫中间件

Spider middleware主要有三个作用：
1、在downloader生成request发送给spider之前，对request进行处理
2、在spider生成request发送给scheduler之前，对request进行处理
3、在spider生成request发送给item pipeline之前，对item进行处理

核心方法

# 返回None或一个异常。
#如果是None,就继续调用其他的spider middleware。
#如果是一个异常，调用request里的errback（）方法，再抛出异常是交给process_spider_exception(response, exception, spider)处理
process_ spider _input(response, spider)

# 必须返回一个包括request或item对象的可迭代对象
process_spider_output(response, result, spider)

# 返回None 或 
# 一个包括request或item对象的可迭代对象
process_spider_exception(response, exception, spider)

#返回一个request对象的可迭代对象
process_start_requests(start_requests, spider)

上述只需要其中一个方法就可以定义一个spider middleware。

本文章为转载内容，我们尊重原作者对文章享有的著作权。如有内容错误或侵权问题，欢迎原作者联系我们进行内容更正或删除文章。