当我尝试通过 ssh 升级 pip 版本 ec2 实例时，出现如下错误
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/pip/basecommand.py", line 209, in main
status = self.run(options, args)
File "/usr/lib/python3/dist-packages/pip/commands/install.py", line 328, in run
wb.build(autobuilding=True)
File "/usr/lib/python3/dist-packages/pip/wheel.py", line 748, in build
self.requirement_set.prepare_files(self.finder)
File "/usr/lib/python3/dist-packages/pip/req/req_set.py", line 360, in prepare_files
ignore_dependencies=self.ignore_dependencies))
File "/usr/lib/python3/dist-packages/pip/req/req_set.py", line 448, in _prepare_file
req_to_install, finder)
File "/usr/lib/python3/dist-packages/pip/req/req_set.py", line 397, in _check_skip_installed
finder.find_requirement(req_to_install, self.upgrade)
File "/usr/lib/python3/dist-packages/pip/index.py", line 442, in find_requirement
all_candidates = self.find_all_candidates(req.name)
File "/usr/lib/python3/dist-packages/pip/index.py", line 400, in find_all_candidates
for page in self._get_pages(url_locations, project_name):
File "/usr/lib/python3/dist-packages/pip/index.py", line 545, in _get_pages
page = self._get_page(location)
File "/usr/lib/python3/dist-packages/pip/index.py", line 648, in _get_page
return HTMLPage.get_page(link, session=self.session)
File "/usr/lib/python3/dist-packages/pip/index.py", line 757, in get_page
"Cache-Control": "max-age=600",
File "/usr/share/python-wheels/requests-2.9.1-py2.py3-none-any.whl/requests/sessions.py", line 480, in get
return self.request('GET', url, **kwargs)
File "/usr/lib/python3/dist-packages/pip/download.py", line 378, in request
return super(PipSession, self).request(method, url, *args, **kwargs)
File "/usr/share/python-wheels/requests-2.9.1-py2.py3-none-any.whl/requests/sessions.py", line 468, in request
resp = self.send(prep, **send_kwargs)
File "/usr/share/python-wheels/requests-2.9.1-py2.py3-none-any.whl/requests/sessions.py", line 576, in send
r = adapter.send(request, **kwargs)
File "/usr/share/python-wheels/CacheControl-0.11.5-py2.py3-none-any.whl/cachecontrol/adapter.py", line 46, in send
resp = super(CacheControlAdapter, self).send(request, **kw)
File "/usr/share/python-wheels/requests-2.9.1-py2.py3-none-any.whl/requests/adapters.py", line 376, in send
timeout=timeout
File "/usr/share/python-wheels/urllib3-1.13.1-py2.py3-none-any.whl/urllib3/connectionpool.py", line 610, in urlopen
_stacktrace=sys.exc_info()[2])
File "/usr/share/python-wheels/urllib3-1.13.1-py2.py3-none-any.whl/urllib3/util/retry.py", line 228, in increment
total -= 1
TypeError: unsupported operand type(s) for -=: 'Retry' and 'int'