Scrapy爬虫Response子类在应用中的问题解析

今天用scrapy爬取壁纸的时候（url：http://pic.netbian.com/4kmein...）絮叨了一些问题，记录下来，供后世探讨，以史为鉴。**

因为网站是动态渲染的，所以选择scrapy对接selenium（scrapy抓取网页的方式和requests库相似，都是直接模拟HTTP请求，而Scrapy也不能抓取JavaScript动态渲染的网页。）

所以在Downloader Middlewares中需要得到Request并且返回一个Response，问题出在Response，通过查看官方文档发现class scrapy.http.Response(url[, status=200, headers=None, body=b'', flags=None, request=None])，随即通过from scrapy.http import Response导入Response

输入scrapy crawl girl得到如下错误：

*results=response.xpath('//[@id="main"]/div[3]/ul/lia/img')
raise NotSupported("Response content isn't text")
scrapy.exceptions.NotSupported: Response content isn't text**

检查相关代码：

# middlewares.py
from scrapy import signals
from scrapy.http import Response
from scrapy.exceptions import IgnoreRequest
import selenium
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
class Pic4KgirlDownloaderMiddleware(object):
   # 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.
   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
       try:
           self.browser=selenium.webdriver.Chrome()
           self.wait=WebDriverWait(self.browser,10)
           self.browser.get(request.url)
           self.wait.until(EC.presence_of_element_located((By.CSS_SELECTOR, '#main > div.page > a:nth-child(10)')))
           return Response(url=request.url,status=200,request=request,body=self.browser.page_source.encode('utf-8'))
       #except:
           #raise IgnoreRequest()
       finally:
           self.browser.close()

推断问题出在：

return Response(url=request.url,status=200,request=request,body=self.browser.page_source.encode('utf-8'))

查看Response类的定义

@property
   def text(self):
       """For subclasses of TextResponse, this will return the body
       as text (unicode object in Python 2 and str in Python 3)
       """
       raise AttributeError("Response content isn't text")
   def css(self, *a, **kw):
       """Shortcut method implemented only by responses whose content
       is text (subclasses of TextResponse).
       """
       raise NotSupported("Response content isn't text")
   def xpath(self, *a, **kw):
       """Shortcut method implemented only by responses whose content
       is text (subclasses of TextResponse).
       """
       raise NotSupported("Response content isn't text")

说明Response类不可以被直接使用，需要被继承重写方法后才能使用

响应子类

**TextResponse对象**
class scrapy.http.TextResponse(url[, encoding[, ...]])
**HtmlResponse对象**
class scrapy.http.HtmlResponse(url[, ...])
**XmlResponse对象**
class scrapy.http.XmlResponse（url [，... ] ）

举例观察TextResponse的定义from scrapy.http import TextResponse

导入TextResponse发现

class TextResponse(Response):
   _DEFAULT_ENCODING = 'ascii'
   def __init__(self, *args, **kwargs):
       self._encoding = kwargs.pop('encoding', None)
       self._cached_benc = None
       self._cached_ubody = None
       self._cached_selector = None
       super(TextResponse, self).__init__(*args, **kwargs)

其中xpath方法已经被重写

@property
   def selector(self):
       from scrapy.selector import Selector
       if self._cached_selector is None:
           self._cached_selector = Selector(self)
       return self._cached_selector
   def xpath(self, query, **kwargs):
       return self.selector.xpath(query, **kwargs)
   def css(self, query):
       return self.selector.css(query)

所以用户想要调用Response类，必须选择调用其子类,并且重写部分方法

Scrapy爬虫入门教程十一 Request和Response（请求和响应）

scrapy文档：https://doc.scrapy.org/en/lat...

中文翻译文档：https://www.jb51.net/article/248161.htm

来源：https://segmentfault.com/a/1190000018449717