python - AttributeError: 'NoneType' object has no attribute 'startswith' -

using pip, happened. after that, pip didn't work anymore. every installation using pip show exception.

exception: traceback (most recent call last):   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\basecommand.py", line 215, in main     status = self.run(options, args)   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\commands\install.py", line 324, in run     requirement_set.prepare_files(finder)   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\req\req_set.py", line 380, in prepare_files     ignore_dependencies=self.ignore_dependencies))   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\req\req_set.py", line 487, in _prepare_file     req_to_install, finder)   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\req\req_set.py", line 428, in _check_skip_installed     req_to_install, upgrade_allowed)   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\index.py", line 465, in find_requirement     all_candidates = self.find_all_candidates(req.name)   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\index.py", line 423, in find_all_candidates     page in self._get_pages(url_locations, project_name):   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\index.py", line 568, in _get_pages     page = self._get_page(location)   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\index.py", line 683, in _get_page     return htmlpage.get_page(link, session=self.session)   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\index.py", line 792, in get_page     "cache-control": "max-age=600",   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\_vendor\requests\sessions.py", line 488, in     return self.request('get', url, **kwargs)   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\download.py", line 386, in request     return super(pipsession, self).request(method, url, *args, **kwargs)   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\_vendor\requests\sessions.py", line 475, in request     resp = self.send(prep, **send_kwargs)   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\_vendor\requests\sessions.py", line 596, in send     r = adapter.send(request, **kwargs)   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\_vendor\cachecontrol\adapter.py", line 47, in send     resp = super(cachecontroladapter, self).send(request, **kw)   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\_vendor\requests\adapters.py", line 423, in send     timeout=timeout   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\_vendor\requests\packages\urllib3\connectionpool.py", line 589, in urlopen     self._prepare_proxy(conn)   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\_vendor\requests\packages\urllib3\connectionpool.py", line 797, in _prepare_proxy     conn.connect()   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\_vendor\requests\packages\urllib3\connection.py", line 254, in connect     conn = self._new_conn()   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\_vendor\requests\packages\urllib3\connection.py", line 142, in _new_conn     (self.host, self.port), self.timeout, **extra_kw)   file "c:\users\houyin~1\appdata\local\temp\tmpfofjoh\pip.zip\pip\_vendor\requests\packages\urllib3\util\connection.py", line 66, in create_connection     if host.startswith('['): attributeerror: 'nonetype' object has no attribute 'startswith'