python pip upgrade breaks
<p>I am using Ubuntu 16.04.1 LTS at work.
I need to upgrade pip to latest version(8.1.2)</p>

<p>When I run:</p>

<pre><code>sudo pip install -U pip
</code></pre>

<p>I get following error. I checked the proxy, they look okay.    </p>

<pre><code>Exception:    
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/pip/basecommand.py", line 209, in main    
    status = self.run(options, args)    
  File "/usr/lib/python2.7/dist-packages/pip/commands/install.py", line 328, in run 
    wb.build(autobuilding=True)  
  File "/usr/lib/python2.7/dist-packages/pip/wheel.py", line 748, in build    
    self.requirement_set.prepare_files(self.finder)  
  File "/usr/lib/python2.7/dist-packages/pip/req/req_set.py", line 360, in prepare_files    
    ignore_dependencies=self.ignore_dependencies))    
  File "/usr/lib/python2.7/dist-packages/pip/req/req_set.py", line 448, in _prepare_file    
    req_to_install, finder)
  File "/usr/lib/python2.7/dist-packages/pip/req/req_set.py", line 397, in _check_skip_installed    
    finder.find_requirement(req_to_install, self.upgrade)
  File "/usr/lib/python2.7/dist-packages/pip/index.py", line 442, in find_requirement
    all_candidates = self.find_all_candidates(req.name)    
  File "/usr/lib/python2.7/dist-packages/pip/index.py", line 400, in find_all_candidates    
    for page in self._get_pages(url_locations, project_name):    
  File "/usr/lib/python2.7/dist-packages/pip/index.py", line 545, in _get_pages    
    page = self._get_page(location)    
  File "/usr/lib/python2.7/dist-packages/pip/index.py", line 648, in _get_page    
    return HTMLPage.get_page(link, session=self.session)    
  File "/usr/lib/python2.7/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/python2.7/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'
</code></pre>

<p>Somebody give me some pointer.</p>

<p>This is the command i use:</p>

<pre><code>pip install --upgrade pip
</code></pre>

python linux pip upgrade