xpath表达式，爬虫无法爬取

Question

这个表达式哪里出错了，我无法爬取网页的东西
```python
import requests
import pandas as pd
from lxml import etree
from bs4 import BeautifulSoup

headers={'User-Agent':'Mozilla/5.0(Windows NT 10.0;win64;x64)ApplewebKit/537.36(KHTML,like Gecko)Chrome/78.0.3904.108Safari/537.36'}

for i in range(1,26):
    url=r"http://bang.dangdang.com/books/bestsellers/01.00.00.00.00.00-recent30-0-0-1-{}".format(i)
    html_date=requests.get(url,headers=headers,timeout=10)
    html_text=html_date.text
    #print(html_text)
    html=etree.HTML(html_text)
    print(html.xpath("/html/body/div[3]/div[3]/div[2]/ul/li[1]/div[2]/a/img[@class='alt']"))

```

Answer 1

import requests
import pandas as pd
from lxml import etree
from bs4 import BeautifulSoup

headers = {
    'User-Agent': 'Mozilla/5.0(Windows NT 10.0;win64;x64)ApplewebKit/537.36(KHTML,like Gecko)Chrome/78.0.3904.108Safari/537.36'}

for i in range(1, 26):
    url = "http://bang.dangdang.com/books/bestsellers/01.00.00.00.00.00-recent30-0-0-1-{}".format(i)
    html_date = requests.get(url, headers=headers, timeout=10)
    html_text = html_date.text
    # print(html_text)
    html = etree.HTML(html_text)
    print(  html.xpath('//ul[@class="bang_list clearfix bang_list_mode"]/li/div[@class="pic"]/a/img/@alt')  )     #从源代码里面找到的