scrapy爬虫xpath().extract()[0]获取内容报list index out of range错

Question

小弟新手，在看着教程写scrapy爬虫时使用xpath().extract()[0]的方法获取内容，报IndexError: list index out of range错误，求问大神怎么解决，急求答案在线等。（试过去掉.extract()[0]，会报出TypeError: Request url must be str or unicode错误）。代码如下：

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cnblog_spider.py

# -*- coding:utf-8 -*-
# !/usr/bin/env python
import scrapy
from bs4 import BeautifulSoup
from scrapy import Selector

from p1.items import CnblogsSpiderItem


class CnblogsSpider(scrapy.spiders.Spider):
    name = "cnblogs" # 爬虫的名称
    allowed_domains = ["cnblogs.com"]# 允许的域名
    start_urls = [
        "http://www.cnblogs.com/qiyeboy/default.html? page=1"
    ]
    def parse(self,response):
        # 实现网页的解析
        # 首先抽取所有的文章
        papers = response.xpath(".//*[@class='day']")#.extract()
        # 从每篇文章中抽取数据
        #soup = BeautifulSoup(papers, "html.parser", from_encoding="utf-8")
        # print papers
        for paper in papers:
            url = paper.xpath(".//*[@class='pastTitle']/a/@href").extract()[0]
            title = paper.xpath(".//*[@class='pastTitle']/a").extract()[0]
            time = paper.xpath(".//*[@class='dayTitle']/a").extract()[0]
            content = paper.xpath(".//*[@class='postCon']/a").extract()[0]
            # print url, title, time, content
            item = CnblogsSpiderItem(url=url, title=title, time=time, content=content)
            request = scrapy.Request(url=url, callback=self.parse_body)
            request.meta['item'] = item  # 将item暂存
            yield request
            #yield item
        next_page = Selector(response).re(u'<a href="(\S*)">下一页</a>')
        if next_page:
            yield scrapy.Request(url=next_page[0], callback=self.parse)

    def parse_body(self, response):
        item = response.meta['item']
        body = response.xpath(".//*[@class='postBody']")
        item['cimage_urls'] = body.xpath('.//img//@src').extract()
        yield item

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Answer 1

应该是没爬到数据
最好的办法是在xpath().extract()[0]打个断点，看看数据取到了没
我以前也遇到过这种问题，是xpath写的不对，所以没爬到页面数据。

Answer 2

超出列表范围而且还是［0］，那肯定就是空列表了，看看xpath是不是提取错了

Answer 3

先进行非空判断，在执行业务逻辑，这个问题多半是没有获取到数据

Answer 4

网页的结构发生了变化。
语句应对应修改为：
content = paper.xpath(".//*[@class='postCon']/div/text()").extract()[0]