一、报错再现
我准备了一个工具环境，这里面有一些工具包需要安装，当我运行一下代码：
pip install -r requirements-cpu.txt
回车过后，发生了如下报错：
ERROR: Exception:
Traceback (most recent call last):
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\cli\base_command.py", line 173, in _main
status = self.run(options, args)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\cli\req_command.py", line 203, in wrapper
return func(self, options, args)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\commands\install.py", line 316, in run
reqs, check_supported_wheels=not options.target_dir
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\resolution\resolvelib\resolver.py", line 95, in resolve
collected.requirements, max_rounds=try_to_avoid_resolution_too_deep
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_vendor\resolvelib\resolvers.py", line 472, in resolve
state = resolution.resolve(requirements, max_rounds=max_rounds)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_vendor\resolvelib\resolvers.py", line 341, in resolve
self._add_to_criteria(self.state.criteria, r, parent=None)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_vendor\resolvelib\resolvers.py", line 172, in _add_to_criteria
if not criterion.candidates:
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_vendor\resolvelib\structs.py", line 151, in __bool__
return bool(self._sequence)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\resolution\resolvelib\found_candidates.py", line 140, in __bool__
return any(self)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\resolution\resolvelib\found_candidates.py", line 128, in <genexpr>
return (c for c in iterator if id(c) not in self._incompatible_ids)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\resolution\resolvelib\found_candidates.py", line 29, in _iter_built
for version, func in infos:
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\resolution\resolvelib\factory.py", line 275, in iter_index_candidate_infos
hashes=hashes,
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\index\package_finder.py", line 851, in find_best_candidate
candidates = self.find_all_candidates(project_name)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\index\package_finder.py", line 798, in find_all_candidates
page_candidates = list(page_candidates_it)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\index\sources.py", line 134, in page_candidates
yield from self._candidates_from_page(self._link)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\index\package_finder.py", line 758, in process_project_url
html_page = self._link_collector.fetch_page(project_url)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\index\collector.py", line 490, in fetch_page
return _get_html_page(location, session=self.session)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\index\collector.py", line 400, in _get_html_page
resp = _get_html_response(url, session=session)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\index\collector.py", line 132, in _get_html_response
"Cache-Control": "max-age=0",
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_vendor\requests\sessions.py", line 555, in get
return self.request('GET', url, **kwargs)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_internal\network\session.py", line 454, in request
return super().request(method, url, *args, **kwargs)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_vendor\requests\sessions.py", line 542, in request
resp = self.send(prep, **send_kwargs)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_vendor\requests\sessions.py", line 655, in send
r = adapter.send(request, **kwargs)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_vendor\cachecontrol\adapter.py", line 53, in send
resp = super(CacheControlAdapter, self).send(request, **kw)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_vendor\requests\adapters.py", line 449, in send
timeout=timeout
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_vendor\urllib3\connectionpool.py", line 696, in urlopen
self._prepare_proxy(conn)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_vendor\urllib3\connectionpool.py", line 964, in _prepare_proxy
conn.connect()
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_vendor\urllib3\connection.py", line 359, in connect
conn = self._connect_tls_proxy(hostname, conn)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_vendor\urllib3\connection.py", line 506, in _connect_tls_proxy
ssl_context=ssl_context,
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_vendor\urllib3\util\ssl_.py", line 453, in ssl_wrap_socket
ssl_sock = _ssl_wrap_socket_impl(sock, context, tls_in_tls)
File "D:\Anaconda\envs\rknn\lib\site-packages\pip\_vendor\urllib3\util\ssl_.py", line 495, in _ssl_wrap_socket_impl
return ssl_context.wrap_socket(sock)
File "D:\Anaconda\envs\rknn\lib\ssl.py", line 407, in wrap_socket
_context=self, _session=session)
File "D:\Anaconda\envs\rknn\lib\ssl.py", line 773, in __init__
raise ValueError("check_hostname requires server_hostname")
ValueError: check_hostname requires server_hostname
报错的关键句是：
ValueError: check_hostname requires server_hostname
二、原因分析
从报错的关键句看，他这个错误通常意味着在进行 HTTPS 请求时缺少了服务器的主机名信息，这可能由以下原因导致：
检查网络连接和代理设置：确保你的网络连接正常，没有任何代理设置干扰了 HTTPS 请求的正常进行。
更新 OpenSSL：有时候旧版本的 OpenSSL 会导致一些 SSL/TLS 相关的问题。尝试更新 OpenSSL 到最新版本，或者升级你的 Python 或者相关的库到最新版本。
检查 SSL/TLS 配置：如果你有自定义的 SSL/TLS 配置，例如在使用自签名证书或者需要特定的 SSL/TLS 版本，确保这些配置正确并且与服务器配置相匹配。
检查 URL 和请求：确认你的请求的 URL 是正确的，并且没有拼写错误或者其他问题。
三、解决方案
大部分是产生于原因②，因为你正在使用一些代理软件。（反正我是这个原因导致的）例如：V2ray, SSR,Charles,Fiddler,mitm,…
如果真的是这样，那么你关掉代理软件或者清空系统代理，再重新运行之前失败的命令，我相信应该能解决问题了。
四、参考文献
[1]Stack Overflow. (2021). ValueError: check_hostname requires server_hostname. [Online Forum Comment]. Stack Overflow. Retrieved November 3, 2023, from https://stackoverflow.com/questions/67297278/valueerror-check-hostname-requires-server-hostname
