摘要：今天用爬取壁紙的時(shí)候絮叨了一些問題，記錄下來，供后世探討，以史為鑒。因?yàn)榫W(wǎng)站是動(dòng)態(tài)渲染的，所以選擇對(duì)接抓取網(wǎng)頁的方式和庫相似，都是直接模擬請(qǐng)求，而也不能抓取動(dòng)態(tài)渲染的網(wǎng)頁。

今天用scrapy爬取壁紙的時(shí)候（url：http://pic.netbian.com/4kmein...）絮叨了一些問題，記錄下來，供后世探討，以史為鑒。**

因?yàn)榫W(wǎng)站是動(dòng)態(tài)渲染的，所以選擇scrapy對(duì)接selenium（scrapy抓取網(wǎng)頁的方式和requests庫相似，都是直接模擬HTTP請(qǐng)求，而Scrapy也不能抓取JavaScript動(dòng)態(tài)渲染的網(wǎng)頁。）

所以在Downloader Middlewares中需要得到Request并且返回一個(gè)Response，問題出在Response，通過查看官方文檔發(fā)現(xiàn)class scrapy.http.Response(url[, status=200, headers=None, body=b"", flags=None, request=None])，隨即通過from scrapy.http import Response導(dǎo)入Response

輸入scrapy crawl girl
得到如下錯(cuò)誤：
*results=response.xpath("http://[@id="main"]/div[3]/ul/lia/img")
raise NotSupported("Response content isn"t text")
scrapy.exceptions.NotSupported: Response content isn"t text**
檢查相關(guān)代碼：

# 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()

推斷問題出在：
return Response(url=request.url,status=200,request=request,body=self.browser.page_source.encode("utf-8"))
查看Response類的定義發(fā)現(xiàn)：

@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")

說明Response類不可以被直接使用，需要被繼承重寫方法后才能使用

響應(yīng)子類：

**TextResponse對(duì)象**
class scrapy.http.TextResponse(url[, encoding[, ...]])
**HtmlResponse對(duì)象**
class scrapy.http.HtmlResponse(url[, ...])
**XmlResponse對(duì)象**
class scrapy.http.XmlResponse（url [，... ] ）

舉例觀察TextResponse的定義
from scrapy.http import TextResponse
導(dǎo)入TextResponse
發(fā)現(xiàn)

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方法已經(jīng)被重寫

@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)

所以用戶想要調(diào)用Response類，必須選擇調(diào)用其子類,并且重寫部分方法

Scrapy爬蟲入門教程十一 Request和Response（請(qǐng)求和響應(yīng)）

scrapy文檔：https://doc.scrapy.org/en/lat...
中文翻譯文檔：https://blog.csdn.net/Inke88/...