scrapy之中间件
1 Dowloader Middeware
下载中间件的用途 1、在process——request内，自定义下载，不用scrapy的下载 2、对请求进行二次加工，比如 设置请求头 设置cookie 添加代理 scrapy自带的代理组件： from scrapy.downloadermiddlewares.httpproxy import HttpProxyMiddleware from urllib.request import getproxies
class DownMiddleware1(object): def process_request(self, request, spider): """ 请求需要被下载时，经过所有下载器中间件的process_request调用 :param request: :param spider: :return: None,继续后续中间件去下载； Response对象，停止process_request的执行，开始执行process_response Request对象，停止中间件的执行，将Request重新调度器 raise IgnoreRequest异常，停止process_request的执行，开始执行process_exception """ pass def process_response(self, request, response, spider): """ spider处理完成，返回时调用 :param response: :param result: :param spider: :return: Response 对象：转交给其他中间件process_response Request 对象：停止中间件，request会被重新调度下载 raise IgnoreRequest 异常：调用Request.errback """ print('response1') return response def process_exception(self, request, exception, spider): """ 当下载处理器(download handler)或 process_request() (下载中间件)抛出异常 :param response: :param exception: :param spider: :return: None：继续交给后续中间件处理异常； Response对象：停止后续process_exception方法 Request对象：停止中间件，request将会被重新调用下载 """ return None
#1、与middlewares.py同级目录下新建proxy_handle.py import requests def get_proxy(): return requests.get("http://127.0.0.1:5010/get/").text def delete_proxy(proxy): requests.get("http://127.0.0.1:5010/delete/?proxy={}".format(proxy)) #2、middlewares.py from Amazon.proxy_handle import get_proxy,delete_proxy class DownMiddleware1(object): def process_request(self, request, spider): """ 请求需要被下载时，经过所有下载器中间件的process_request调用 :param request: :param spider: :return: None,继续后续中间件去下载； Response对象，停止process_request的执行，开始执行process_response Request对象，停止中间件的执行，将Request重新调度器 raise IgnoreRequest异常，停止process_request的执行，开始执行process_exception """ proxy="http://" + get_proxy() request.meta['download_timeout']=20 request.meta["proxy"] = proxy print('为%s 添加代理%s ' % (request.url, proxy),end='') print('元数据为',request.meta) def process_response(self, request, response, spider): """ spider处理完成，返回时调用 :param response: :param result: :param spider: :return: Response 对象：转交给其他中间件process_response Request 对象：停止中间件，request会被重新调度下载 raise IgnoreRequest 异常：调用Request.errback """ print('返回状态吗',response.status) return response def process_exception(self, request, exception, spider): """ 当下载处理器(download handler)或 process_request() (下载中间件)抛出异常 :param response: :param exception: :param spider: :return: None：继续交给后续中间件处理异常； Response对象：停止后续process_exception方法 Request对象：停止中间件，request将会被重新调用下载 """ print('代理%s，访问%s出现异常:%s' %(request.meta['proxy'],request.url,exception)) import time time.sleep(5) delete_proxy(request.meta['proxy'].split("//")[-1]) request.meta['proxy']='http://'+get_proxy() return request
2 Spider Middleware
1、爬虫中间件方法介绍
from scrapy import signals class SpiderMiddleware(object): # 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) #当前爬虫执行时触发spider_opened return s def spider_opened(self, spider): # spider.logger.info('我是egon派来的爬虫1: %s' % spider.name) print('我是egon派来的爬虫1: %s' % spider.name) 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). print('start_requests1') for r in start_requests: yield r def process_spider_input(self, response, spider): # Called for each response that goes through the spider # middleware and into the spider. # 每个response经过爬虫中间件进入spider时调用 # 返回值：Should return None or raise an exception. #1、None: 继续执行其他中间件的process_spider_input #2、抛出异常： # 一旦抛出异常则不再执行其他中间件的process_spider_input # 并且触发request绑定的errback # errback的返回值倒着传给中间件的process_spider_output # 如果未找到errback，则倒着执行中间件的process_spider_exception print("input1") 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, dict or Item objects. print('output1') # 用yield返回多次，与return返回一次是一个道理 # 如果生成器掌握不好（函数内有yield执行函数得到的是生成器而并不会立刻执行），生成器的形式会容易误导你对中间件执行顺序的理解 # for i in result: # yield i return result 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 Response, dict # or Item objects. print('exception1')
2、当前爬虫启动时以及初始请求产生时
#步骤一： ''' 打开注释： SPIDER_MIDDLEWARES = { 'Baidu.middlewares.SpiderMiddleware1': 200, 'Baidu.middlewares.SpiderMiddleware2': 300, 'Baidu.middlewares.SpiderMiddleware3': 400, } ''' #步骤二：middlewares.py from scrapy import signals class SpiderMiddleware1(object): @classmethod def from_crawler(cls, crawler): s = cls() crawler.signals.connect(s.spider_opened, signal=signals.spider_opened) #当前爬虫执行时触发spider_opened return s def spider_opened(self, spider): print('我是egon派来的爬虫1: %s' % spider.name) def process_start_requests(self, start_requests, spider): # Must return only requests (not items). print('start_requests1') for r in start_requests: yield r class SpiderMiddleware2(object): @classmethod def from_crawler(cls, crawler): s = cls() crawler.signals.connect(s.spider_opened, signal=signals.spider_opened) # 当前爬虫执行时触发spider_opened return s def spider_opened(self, spider): print('我是egon派来的爬虫2: %s' % spider.name) def process_start_requests(self, start_requests, spider): print('start_requests2') for r in start_requests: yield r class SpiderMiddleware3(object): @classmethod def from_crawler(cls, crawler): s = cls() crawler.signals.connect(s.spider_opened, signal=signals.spider_opened) # 当前爬虫执行时触发spider_opened return s def spider_opened(self, spider): print('我是egon派来的爬虫3: %s' % spider.name) def process_start_requests(self, start_requests, spider): print('start_requests3') for r in start_requests: yield r #步骤三：分析运行结果 #1、启动爬虫时则立刻执行： 我是egon派来的爬虫1: baidu 我是egon派来的爬虫2: baidu 我是egon派来的爬虫3: baidu #2、然后产生一个初始的request请求，依次经过爬虫中间件1,2,3： start_requests1 start_requests2 start_requests3
3、process_spider_input返回None时
#步骤一：打开注释： SPIDER_MIDDLEWARES = { 'Baidu.middlewares.SpiderMiddleware1': 200, 'Baidu.middlewares.SpiderMiddleware2': 300, 'Baidu.middlewares.SpiderMiddleware3': 400, } ''' #步骤二：middlewares.py from scrapy import signals class SpiderMiddleware1(object): def process_spider_input(self, response, spider): print("input1") def process_spider_output(self, response, result, spider): print('output1') return result def process_spider_exception(self, response, exception, spider): print('exception1') class SpiderMiddleware2(object): def process_spider_input(self, response, spider): print("input2") return None def process_spider_output(self, response, result, spider): print('output2') return result def process_spider_exception(self, response, exception, spider): print('exception2') class SpiderMiddleware3(object): def process_spider_input(self, response, spider): print("input3") return None def process_spider_output(self, response, result, spider): print('output3') return result def process_spider_exception(self, response, exception, spider): print('exception3') #步骤三：运行结果分析 #1、返回response时，依次经过爬虫中间件1,2,3 input1 input2 input3 #2、spider处理完毕后，依次经过爬虫中间件3,2,1 output3 output2 output1
4、process_spider_input抛出异常时
#步骤一： ''' 打开注释： SPIDER_MIDDLEWARES = { 'Baidu.middlewares.SpiderMiddleware1': 200, 'Baidu.middlewares.SpiderMiddleware2': 300, 'Baidu.middlewares.SpiderMiddleware3': 400, } ''' #步骤二：middlewares.py from scrapy import signals class SpiderMiddleware1(object): def process_spider_input(self, response, spider): print("input1") def process_spider_output(self, response, result, spider): print('output1') return result def process_spider_exception(self, response, exception, spider): print('exception1') class SpiderMiddleware2(object): def process_spider_input(self, response, spider): print("input2") raise Type def process_spider_output(self, response, result, spider): print('output2') return result def process_spider_exception(self, response, exception, spider): print('exception2') class SpiderMiddleware3(object): def process_spider_input(self, response, spider): print("input3") return None def process_spider_output(self, response, result, spider): print('output3') return result def process_spider_exception(self, response, exception, spider): print('exception3') #运行结果 input1 input2 exception3 exception2 exception1 #分析： #1、当response经过中间件1的 process_spider_input返回None，继续交给中间件2的process_spider_input #2、中间件2的process_spider_input抛出异常，则直接跳过后续的process_spider_input，将异常信息传递给Spiders里该请求的errback #3、没有找到errback，则该response既没有被Spiders正常的callback执行，也没有被errback执行，即Spiders啥事也没有干，那么开始倒着执行process_spider_exception #4、如果process_spider_exception返回None，代表该方法推卸掉责任，并没处理异常，而是直接交给下一个process_spider_exception，全都返回None，则异常最终交给Engine抛出
5、指定errback
#步骤一：spider.py import scrapy class BaiduSpider(scrapy.Spider): name = 'baidu' allowed_domains = ['www.baidu.com'] start_urls = ['http://www.baidu.com/'] def start_requests(self): yield scrapy.Request(url='http://www.baidu.com/', callback=self.parse, errback=self.parse_err, ) def parse(self, response): pass def parse_err(self,res): #res 为异常信息，异常已经被该函数处理了，因此不会再抛给因此，于是开始走process_spider_output return [1,2,3,4,5] #提取异常信息中有用的数据以可迭代对象的形式存放于管道中，等待被process_spider_output取走 #步骤二： ''' 打开注释： SPIDER_MIDDLEWARES = { 'Baidu.middlewares.SpiderMiddleware1': 200, 'Baidu.middlewares.SpiderMiddleware2': 300, 'Baidu.middlewares.SpiderMiddleware3': 400, } ''' #步骤三：middlewares.py from scrapy import signals class SpiderMiddleware1(object): def process_spider_input(self, response, spider): print("input1") def process_spider_output(self, response, result, spider): print('output1',list(result)) return result def process_spider_exception(self, response, exception, spider): print('exception1') class SpiderMiddleware2(object): def process_spider_input(self, response, spider): print("input2") raise TypeError('input2 抛出异常') def process_spider_output(self, response, result, spider): print('output2',list(result)) return result def process_spider_exception(self, response, exception, spider): print('exception2') class SpiderMiddleware3(object): def process_spider_input(self, response, spider): print("input3") return None def process_spider_output(self, response, result, spider): print('output3',list(result)) return result def process_spider_exception(self, response, exception, spider): print('exception3') #步骤四：运行结果分析 input1 input2 output3 [1, 2, 3, 4, 5] #parse_err的返回值放入管道中，只能被取走一次，在output3的方法内可以根据异常信息封装一个新的request请求 output2 [] output1 []
