title: OS X pip3 broken with brew install python3.6.5_1
body: <p>I just did a fresh install of python3 (3.6.5_1) on Mac OS (High Sierra) and pip3 does not work. I get the following error with pip3:</p>
  
  <pre><code>Traceback (most recent call last):
    File "/usr/local/bin/pip3", line 11, in &lt;module&gt;
      load_entry_point('pip==10.0.1', 'console_scripts', 'pip3')()
    File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 476, in load_entry_point
      return get_distribution(dist).load_entry_point(group, name)
    File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2700, in load_entry_point
      return ep.load()
    File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2318, in load
      return self.resolve()
    File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2324, in resolve
      module = __import__(self.module_name, fromlist=['__name__'], level=0)
    File "/usr/local/lib/python3.6/site-packages/pip/_internal/__init__.py", line 42, in &lt;module&gt;
      from pip._internal import cmdoptions
    File "/usr/local/lib/python3.6/site-packages/pip/_internal/cmdoptions.py", line 16, in &lt;module&gt;
      from pip._internal.index import (
    File "/usr/local/lib/python3.6/site-packages/pip/_internal/index.py", line 39, in &lt;module&gt;
      from pip._internal.wheel import Wheel, wheel_ext
    File "/usr/local/lib/python3.6/site-packages/pip/_internal/wheel.py", line 7, in &lt;module&gt;
      import compileall
    File "/usr/local/Cellar/python/3.6.5_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><code>which pip3</code> returns <code>/usr/local/bin/pip3</code></p>
  
  <p>I have searched and can't find a solution.</p>