404 HTTP 错误，尽管能够在浏览器中看到该页面

Question

我正在尝试绘制此网站的地图，但在尝试完全抓取它时遇到了问题。我收到错误 404，即使 URL 存在。

这是我的代码：

import csv
from urllib.request import urlopen
from bs4 import BeautifulSoup
import re

csvFile = open("C:/Users/Pichau/codigo/govbr/brasil/govfederal/govbr/arquivos/teste.txt",'wt')
paginas = set()
def getLinks(pageUrl):
    global paginas
    html = urlopen("https://www.gov.br/pt-br/"+pageUrl)
    bsObj = BeautifulSoup(html, "html.parser")
    writer = csv.writer(csvFile)
    for link in bsObj.findAll("a"):
      if 'href' in link.attrs:
       if link.attrs['href'] not in paginas:
             #nova página encontrada
                newPage = link.attrs['href']
                print(newPage)
                paginas.add(newPage)
                getLinks(newPage)
                csvRow = []
                csvRow.append(newPage)
                writer.writerow(csvRow)

   
getLinks("")
csvFile.close()

这是我收到的错误消息，在我尝试运行该代码后：

#wrapper
/
#main-navigation
#nolivesearchGadget
#tile-busca-input
#portal-footer
http://brasil.gov.br
Traceback (most recent call last):
  File "c:\Users\Pichau\codigo\govbr\brasil\govfederal\govbr\teste2.py", line 26, in <module>
    getLinks("")
  File "c:\Users\Pichau\codigo\govbr\brasil\govfederal\govbr\teste2.py", line 20, in getLinks
    getLinks(newPage)
  File "c:\Users\Pichau\codigo\govbr\brasil\govfederal\govbr\teste2.py", line 20, in getLinks
    getLinks(newPage)
  File "c:\Users\Pichau\codigo\govbr\brasil\govfederal\govbr\teste2.py", line 20, in getLinks
    getLinks(newPage)
  [Previous line repeated 4 more times]
  File "c:\Users\Pichau\codigo\govbr\brasil\govfederal\govbr\teste2.py", line 10, in getLinks
    html = urlopen("https://www.gov.br/pt-br/"+pageUrl)
  File "C:\Users\Pichau\AppData\Local\Programs\Python\Python39\lib\urllib\request.py", line 214, in urlopen
    return opener.open(url, data, timeout)
  File "C:\Users\Pichau\AppData\Local\Programs\Python\Python39\lib\urllib\request.py", line 523, in open
    response = meth(req, response)
  File "C:\Users\Pichau\AppData\Local\Programs\Python\Python39\lib\urllib\request.py", line 632, in http_response
    response = self.parent.error(
  File "C:\Users\Pichau\AppData\Local\Programs\Python\Python39\lib\urllib\request.py", line 561, in error
    return self._call_chain(*args)
  File "C:\Users\Pichau\AppData\Local\Programs\Python\Python39\lib\urllib\request.py", line 494, in _call_chain
    result = func(*args)
  File "C:\Users\Pichau\AppData\Local\Programs\Python\Python39\lib\urllib\request.py", line 641, in http_error_default
    raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 404: Not Found
PS C:\Users\Pichau\codigo\govbr>

我尝试只用主 link 来做，它工作正常，但是一旦我将 pageurl 变量添加到 url，它就会给出我这个错误。我该如何解决这个错误？

Answer 1

据我所知，您是对的 - 页面就在那里...对于我们这些使用浏览器的人来说。我假设正在发生的是一些基本的 anti-botting 机制，它禁止不常见的 UserAgents，或者换句话说，只允许浏览器查看页面。然而，由于用户代理是我们可以控制的 header，我们可以操纵它，这样它就不会抛出 404 错误。

我现在无法输入代码，但你需要配对 this Whosebug answer describing how to change a header in urllib, and you must write some code which takes that answer and changes the "UserAgent" header to a value like Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.93 Safari/537.36, which I've taken from here。

更改 UserAgent 后 header，您应该能够成功下载页面。

404 HTTP 错误，尽管能够在浏览器中看到该页面

404 HTTP error, despite being able to see the page in the browser

python

beautifulsoup

web-crawler

screen-scraping

urllib