Request/Response【学习笔记03】（requests response）

Request/Response【学习笔记03】（requests response）

Request

Request 部分源码：

# 部分代码class Request(object_ref): def __init__(self, url, callback=None, method='GET', headers=None, body=None, cookies=None, meta=None, encoding='utf-8', priority=0, dont_filter=False, errback=None): self._encoding = encoding # this one has to be set first self.method = str(method).upper() self._set_url(url) self._set_body(body) assert isinstance(priority, int), "Request priority not an integer: %r" % priority self.priority = priority assert callback or not errback, "Cannot use errback without a callback" self.callback = callback self.errback = errback self.cookies = cookies or {} self.headers = Headers(headers or {}, encoding=encoding) self.dont_filter = dont_filter self._meta = dict(meta) if meta else None @property def meta(self): if self._meta is None: self._meta = {} return self._meta

其中，比较常用的参数：

url: 就是需要请求，并进行下一步处理的urlcallback: 指定该请求返回的Response，由那个函数来处理。method: 请求一般不需要指定，默认GET方法，可设置为"GET", "POST", "PUT"等，且保证字符串大写headers: 请求时，包含的头文件。一般不需要。内容一般如下： # 自己写过爬虫的肯定知道 Host: media.readthedocs.org User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:33.0) Gecko/20100101 Firefox/33.0 Accept: text/css,*/*;q=0.1 Accept-Language: zh-cn,zh;q=0.8,en-us;q=0.5,en;q=0.3 Accept-Encoding: gzip, deflate Referer: Cookie: _ga=GA1.2.1612165614.1415584110; Connection: keep-alive If-Modified-Since: Mon, 25 Aug 2014 21:59:35 GMT Cache-Control: max-age=0meta: 比较常用，在不同的请求之间传递数据使用的。字典dict型 request_with_cookies = Request( url=" cookies={'currency': 'USD', 'country': 'UY'}, meta={'dont_merge_cookies': True} )encoding: 使用默认的 'utf-8' 就行。dont_filter: 表明该请求不由调度器过滤。这是当你想使用多次执行相同的请求,忽略重复的过滤器。默认为False。errback: 指定错误处理函数

Response

# 部分代码class Response(object_ref): def __init__(self, url, status=200, headers=None, body='', flags=None, request=None): self.headers = Headers(headers or {}) self.status = int(status) self._set_body(body) self._set_url(url) self.request = request self.flags = [] if flags is None else list(flags) @property def meta(self): try: return self.request.meta except AttributeError: raise AttributeError("Response.meta not available, this response " \ "is not tied to any request")

大部分参数和上面的差不多：

status: 响应码_set_body(body)： 响应体_set_url(url)：响应urlself.request = request

发送POST请求

可以使用​​yield scrapy.FormRequest(url, formdata, callback)​​方法发送POST请求。如果希望程序执行一开始就发送POST请求，可以重写Spider类的​​start_requests(self)​​方法，并且不再调用start_urls里的url。

class mySpider(scrapy.Spider): # start_urls = [" def start_requests(self): url = ' # FormRequest 是Scrapy发送POST请求的方法 yield scrapy.FormRequest( url = url, formdata = {"email" : "mr_mao_hacker@163.com", "password" : "axxxxxxxe"}, callback = self.parse_page ) def parse_page(self, response): # do something

模拟登陆

使用FormRequest.from_response()方法​​模拟用户登录​​

通常网站通过 实现对某些表单字段（如数据或是登录界面中的认证令牌等）的预填充。使用Scrapy抓取网页时，如果想要预填充或重写像用户名、用户密码这些表单字段， 可以使用 FormRequest.from_response() 方法实现。下面是使用这种方法的爬虫例子:

import scrapyclass LoginSpider(scrapy.Spider): name = 'example.com' start_urls = [' def parse(self, response): return scrapy.FormRequest.from_response( response, formdata={'username': 'john', 'password': 'secret'}, callback=self.after_login ) def after_login(self, response): # check login succeed before going on if "authentication failed" in response.body: self.log("Login failed", level=log.ERROR) return # continue scraping with authenticated session...

知乎爬虫案例参考：

zhihuSpider.py爬虫代码

#!/usr/bin/env python# -*- coding:utf-8 -*-from scrapy.spiders import CrawlSpider, Rulefrom scrapy.selector import Selectorfrom scrapy.linkextractors import LinkExtractorfrom scrapy import Request, FormRequestfrom zhihu.items import ZhihuItemclass ZhihuSipder(CrawlSpider) : name = "zhihu" allowed_domains = ["zhihu.com"] start_urls = [ " ] rules = ( Rule(LinkExtractor(allow = ('/question/\d+#.*?', )), callback = 'parse_page', follow = True), Rule(LinkExtractor(allow = ('/question/\d+', )), callback = 'parse_page', follow = True), ) headers = { "Accept": "*/*", "Accept-Language": "en-US,en;q=0.8,zh-TW;q=0.6,zh;q=0.4", "Connection": "keep-alive", "Content-Type":" application/x-charset=UTF-8", "User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2125.111 Safari/537.36", "Referer": " } #重写了爬虫类的方法, 实现了自定义请求, 运行成功后会调用callback回调函数 def start_requests(self): return [Request("meta = {'cookiejar' : 1}, callback = self.post_login)] def post_login(self, response): print 'Preparing login' #下面这句话用于抓取请求网页后返回网页中的_xsrf字段的文字, 用于成功提交表单 xsrf = response.xpath('//input[@name="_xsrf"]/@value').extract()[0] print xsrf #FormRequeset.from_response是Scrapy提供的一个函数, 用于post表单 #登陆成功后, 会调用after_login回调函数 return [FormRequest.from_response(response, #" meta = {'cookiejar' : response.meta['cookiejar']}, headers = self.headers, #注意此处的headers formdata = { '_xsrf': xsrf, 'email': '123456@qq.com', 'password': '123456' }, callback = self.after_login, dont_filter = True )] def after_login(self, response) : for url in self.start_urls : yield self.make_requests_from_url(url) def parse_page(self, response): problem = Selector(response) item = ZhihuItem() item['url'] = response.url item['name'] = problem.xpath('//span[@class="name"]/text()').extract() print item['name'] item['title'] = problem.xpath('//h2[@class="zm-item-title zm-editable-content"]/text()').extract() item['description'] = problem.xpath('//div[@class="zm-editable-content"]/text()').extract() item['answer']= problem.xpath('//div[@class=" zm-editable-content clearfix"]/text()').extract() return item

Item类设置

from scrapy.item import Item, Fieldclass ZhihuItem(Item): # define the fields for your item here like: # name = scrapy.Field() url = Field() #保存抓取问题的url title = Field() #抓取问题的标题 description = Field() #抓取问题的描述 answer = Field() #抓取问题的答案 name = Field() #个人用户的名称

setting.py 设置抓取间隔

BOT_NAME = 'zhihu'SPIDER_MODULES = ['zhihu.spiders']NEWSPIDER_MODULE = 'zhihu.spiders'DOWNLOAD_DELAY = 0.25 #设置下载间隔为250ms

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