error installing scikit-learn

I am trying to install scikit-learn on Ubuntu mate 16.10. For this I am following this guide . When I type pip install -U scikit-learn I get the following error message. Any idea? I have installed python-scipy, python-numpy etc. Exception: Traceback (most recent call last): File "/usr/lib/python2.7/dist-packages/pip/basecommand.py", line 215, 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 750, in build self.requirement_set.prepare_files(self.finder) File "/usr/lib/python2.7/dist-packages/pip/req/req_set.py", line 370, in prepare_files ignore_dependencies=self.ignore_dependencies)) File "/usr/lib/python2.7/dist-packages/pip/req/req_set.py", line 522, in _prepare_file finder, self.upgrade, require_hashes) File "/usr/lib/python2.7/dist-packages/pip/req/req_install.py", line 268, in populate_link self.link = finder.find_requirement(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-2.10.0-py2.py3-none-any.whl/requests/sessions.py", line 487, 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-2.10.0-py2.py3-none-any.whl/requests/sessions.py", line 475, in request resp = self.send(prep, **send_kwargs) File "/usr/share/python-wheels/requests-2.10.0-py2.py3-none-any.whl/requests/sessions.py", line 585, 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-2.10.0-py2.py3-none-any.whl/requests/adapters.py", line 403, in send timeout=timeout File "/usr/share/python-wheels/urllib3-1.15.1-py2.py3-none-any.whl/urllib3/connectionpool.py", line 623, in urlopen _stacktrace=sys.exc_info()) File "/usr/share/python-wheels/urllib3-1.15.1-py2.py3-none-any.whl/urllib3/util/retry.py", line 236, in increment total -= 1 TypeError: unsupported operand type(s) for -=: 'Retry' and 'int'