title: pip install error within Python 3 virtualenv
body: <p>I created a Python 3 virtualenv, like this:</p>
  
  <pre><code>mkproject -p python3 flowerid
  </code></pre>
  
  <p>But when I try to install anything with pip (inside this virtualenv) I get this error:</p>
  
  <pre><code>cd flowerid
  pip install ipython
  Traceback (most recent call last):
    File "/Users/nicolas/.virtualenvs/flowerid/bin/pip", line 11, in &lt;module&gt;
      load_entry_point('pip==9.0.1', 'console_scripts', 'pip')()
    File "/Users/nicolas/.virtualenvs/flowerid/lib/python3.6/site-packages/pkg_resources/__init__.py", line 560, in load_entry_point
      return get_distribution(dist).load_entry_point(group, name)
    File "/Users/nicolas/.virtualenvs/flowerid/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2648, in load_entry_point
      return ep.load()
    File "/Users/nicolas/.virtualenvs/flowerid/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2302, in load
      return self.resolve()
    File "/Users/nicolas/.virtualenvs/flowerid/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2308, in resolve
      module = __import__(self.module_name, fromlist=['__name__'], level=0)
    File "/Users/nicolas/.virtualenvs/flowerid/lib/python3.6/site-packages/pip/__init__.py", line 28, in &lt;module&gt;
      from pip.vcs import git, mercurial, subversion, bazaar  # noqa
    File "/Users/nicolas/.virtualenvs/flowerid/lib/python3.6/site-packages/pip/vcs/subversion.py", line 9, in &lt;module&gt;
      from pip.index import Link
    File "/Users/nicolas/.virtualenvs/flowerid/lib/python3.6/site-packages/pip/index.py", line 31, in &lt;module&gt;
      from pip.wheel import Wheel, wheel_ext
    File "/Users/nicolas/.virtualenvs/flowerid/lib/python3.6/site-packages/pip/wheel.py", line 6, in &lt;module&gt;
      import compileall
    File "/usr/local/Cellar/python3/3.6.1/Frameworks/Python.framework/Versions/3.6/lib/python3.6/compileall.py", line 20, in &lt;module&gt;
      from concurrent.futures import ProcessPoolExecutor
    File "/Library/Python/2.7/site-packages/concurrent/futures/__init__.py", line 8, in &lt;module&gt;
      from concurrent.futures._base import (FIRST_COMPLETED,
    File "/Library/Python/2.7/site-packages/concurrent/futures/_base.py", line 357
      raise type(self._exception), self._exception, self._traceback
                                 ^
  SyntaxError: invalid syntax
  </code></pre>
  
  <p>Everything looks normal until the 'futures' import that goes to "/Library/Python/2.7".</p>
  
  <p>I tried to set "--no-site-packages" when creating the virtualenv, but that doesn't change anything (and it shouldn't as it's the default).</p>
  
  <p>I tried to use pip3 instead, same thing.</p>
  
  <p>I tried to reinstall pip (in the virtualenv) with <code>easy_install pip</code>, same thing...</p>
  
  <p>Any other ideas? Thanks for your help.</p>
  
  <p>Note: I usually use Python 2.7 - I do have many Python 2.7 packages installed globally - perhaps that's what create the conflicts? </p>
  
  <p>I'm on OSX El Capitan.</p>
  
  <p><strong>Update:</strong>
  My virtualenv seems activated - it starts off using the pip and python from my virtualenv. And 'which python' uses python from the virtualenv.</p>
  
  <pre><code>(flowerid) nicolas@~/venv_projects/flowerid$ which python
  /Users/nicolas/.virtualenvs/flowerid/bin/python 
  </code></pre>