"Cannot fetch index base URL" error message when attempting to install scikit-learn for Python 3
<p>I try to install scikit-learn for Python 3. I do it in the following way:</p>

<pre><code>virtualenv model_env
source  model_env/bin/activate
pip3 install sklearn
</code></pre>

<p>As a result I get the following error message:</p>

<pre><code>Downloading/unpacking sklearn
  Cannot fetch index base URL https://pypi.python.org/simple/
  Could not find any downloads that satisfy the requirement sklearn
Cleaning up...
No distributions at all found for sklearn
</code></pre>

<p>I had the same problem with <code>pandas</code> package and I have resolved it by using the following command:</p>

<pre><code>sudo apt-get install python3-pandas
</code></pre>

<p>Unfortunately, the same approach does not work for the <code>sklearn</code></p>

<pre><code>sudo apt-get install python3-sklearn
</code></pre>

<p><strong>ADDED</strong></p>

<p>When I replace <code>sklearn</code> by <code>scikit-learn</code>, I have the same problem:</p>

<pre><code>Downloading/unpacking scikit-learn
  Cannot fetch index base URL https://pypi.python.org/simple/
  Could not find any downloads that satisfy the requirement scikit-learn
Cleaning up...
No distributions at all found for scikit-learn
</code></pre>

<p><strong>ADDED 2</strong></p>

<p>As it has been recommended, I have try to use pip in combination with <code>-vvv</code>. Note that I use <code>pip3</code> instead of <code>pip</code>. This is what I get as the result:</p>

<pre><code>Downloading/unpacking scikit-learn
  Getting page https://pypi.python.org/simple/scikit-learn/
  Could not fetch URL https://pypi.python.org/simple/scikit-learn/: connection error: HTTPSConnectionPool(host='pypi.python.org', port=443): Max retries exceeded with url: /simple/scikit-learn/ (Caused by &lt;class 'OSError'&gt;: [Errno 101] Network is unreachable)
  Will skip URL https://pypi.python.org/simple/scikit-learn/ when looking for download links for scikit-learn
  Getting page https://pypi.python.org/simple/
  Could not fetch URL https://pypi.python.org/simple/: connection error: HTTPSConnectionPool(host='pypi.python.org', port=443): Max retries exceeded with url: /simple/ (Caused by &lt;class 'OSError'&gt;: [Errno 101] Network is unreachable)
  Will skip URL https://pypi.python.org/simple/ when looking for download links for scikit-learn
  Cannot fetch index base URL https://pypi.python.org/simple/
  URLs to search for versions for scikit-learn:
  * https://pypi.python.org/simple/scikit-learn/
  Getting page https://pypi.python.org/simple/scikit-learn/
  Could not fetch URL https://pypi.python.org/simple/scikit-learn/: connection error: HTTPSConnectionPool(host='pypi.python.org', port=443): Max retries exceeded with url: /simple/scikit-learn/ (Caused by &lt;class 'OSError'&gt;: [Errno 101] Network is unreachable)
  Will skip URL https://pypi.python.org/simple/scikit-learn/ when looking for download links for scikit-learn
  Could not find any downloads that satisfy the requirement scikit-learn
Cleaning up...
  Removing temporary dir /tmp/pip_build_root...
No distributions at all found for scikit-learn
Exception information:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/pip/basecommand.py", line 122, in main
    status = self.run(options, args)
  File "/usr/lib/python3/dist-packages/pip/commands/install.py", line 278, in run
    requirement_set.prepare_files(finder, force_root_egg_info=self.bundle, bundle=self.bundle)
  File "/usr/lib/python3/dist-packages/pip/req.py", line 1178, in prepare_files
    url = finder.find_requirement(req_to_install, upgrade=self.upgrade)
  File "/usr/lib/python3/dist-packages/pip/index.py", line 277, in find_requirement
    raise DistributionNotFound('No distributions at all found for %s' % req)
pip.exceptions.DistributionNotFound: No distributions at all found for scikit-learn

Storing debug log for failure in /home/rngorb/.pip/pip.log
</code></pre>