Python "HTTP Error 403: Forbidden"

问题：

执行下面的语句时

 def set_IPlsit():
     url = 'https://www.whatismyip.com/'
     response = urllib.request.urlopen(url)
     html = response.read().decode('utf-8')

出现以下异常:

C:\Users\54353\AppData\Local\Programs\Python\Python36\python.exe "C:/Users/54353/PycharmProjects/untitled/爬虫/图片 - 某网站.py"
Traceback (most recent call last):
  File "C:/Users/54353/PycharmProjects/untitled/爬虫/图片 - 某网站.py", line 100, in <module>
    ip = set_IPlsit2()
  File "C:/Users/54353/PycharmProjects/untitled/爬虫/图片 - 某网站.py", line 95, in set_IPlsit2
    response = ure.urlopen(url)
  File "C:\Users\54353\AppData\Local\Programs\Python\Python36\lib\urllib\request.py", line 223, in urlopen
    return opener.open(url, data, timeout)
  File "C:\Users\54353\AppData\Local\Programs\Python\Python36\lib\urllib\request.py", line 532, in open
    response = meth(req, response)
  File "C:\Users\54353\AppData\Local\Programs\Python\Python36\lib\urllib\request.py", line 642, in http_response
    'http', request, response, code, msg, hdrs)
  File "C:\Users\54353\AppData\Local\Programs\Python\Python36\lib\urllib\request.py", line 570, in error
    return self._call_chain(*args)
  File "C:\Users\54353\AppData\Local\Programs\Python\Python36\lib\urllib\request.py", line 504, in _call_chain
    result = func(*args)
  File "C:\Users\54353\AppData\Local\Programs\Python\Python36\lib\urllib\request.py", line 650, in http_error_default
    raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 403: Forbidden

Process finished with exit code 1

分析：

出现上面的异常是因为用 urllib.request.urlopen 方式打开一个URL，服务器端只会收到一个单纯的对于该页面访问的请求，但是服务器并不知道发送这个请求使用的浏览器，操作系统，硬件平台等信息，而缺失这些信息的请求往往都是非正常的访问，例如爬虫。

有些网站为了防止这种非正常的访问，会验证请求信息中的UserAgent，如果UserAgent存在异常或者是不存在,那么这次请求将会被拒绝。

解决方法：

在请求中添加UserAgent,代码如下

 headers = {'User-Agent':'Mozilla/5.0 (Windows NT 6.1; WOW64; rv:23.0) Gecko/20100101 Firefox/23.0'}
 req = urllib.request.Request(url=chaper_url, headers=headers)
 urllib.request.urlopen(req).read()