Python:Resquest/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url

callback: 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: http://scrapy-chs.readthedocs.org/zh_CN/0.24/
Cookie: _ga=GA1.2.1612165614.1415584110;
Connection: keep-alive
If-Modified-Since: Mon, 25 Aug 2014 21:59:35 GMT
Cache-Control: max-age=0

meta: 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="http://www.example.com",
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url
self.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 = ["http://www.example.com/"]

def start_requests(self):
url = 'http://www.renren.com/PLogin.do'

# 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 scrapy

class LoginSpider(scrapy.Spider):
name = 'example.com'
start_urls = ['http://www.example.com/users/login.php']

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, Rule
from scrapy.selector import Selector
from scrapy.linkextractors import LinkExtractor
from scrapy import Request, FormRequest
from zhihu.items import ZhihuItem

class ZhihuSipder(CrawlSpider) :
name = "zhihu"
allowed_domains = ["www.zhihu.com"]
start_urls = [
"http://www.zhihu.com"
]
rules = (
Rule(LinkExtractor(allow = ('/question/\d+#.*?', )), callback = 'parse_page', follow = True),
Rule(LinkExtractor(allow = ('/question/\d+', )), callback = 'parse_page', follow = True),
)

headers = {
"Accept": "*/*",
"Accept-Encoding": "gzip,deflate",
"Accept-Language": "en-US,en;q=0.8,zh-TW;q=0.6,zh;q=0.4",
"Connection": "keep-alive",
"Content-Type":" application/x-www-form-urlencoded; charset=UTF-8",
"User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/38.0.2125.111 Safari/537.36",
"Referer": "http://www.zhihu.com/"
}

#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("https://www.zhihu.com/login", 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 = Selector(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, #"http://www.zhihu.com/login",
meta = {'cookiejar' : response.meta['cookiejar']},
headers = self.headers, #注意此处的headers
formdata = {
'_xsrf': xsrf,
'email': '1095511864@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, Field

class 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