title: Using Python 3 in virtualenv
body: <p>Using <a href="https://virtualenv.pypa.io/en/latest/">virtualenv</a>, I run my projects with the default version of Python (2.7). On one project, I need to use Python 3.4. </p>
  
  <p>I used <code>brew install python3</code> to install it on my Mac. Now, how do I create a virtualenv that uses the new version?</p>
  
  <p>e.g. sudo virtualenv envPython3</p>
  
  <p>If I try:</p>
  
  <pre><code>virtualenv -p python3 test
  </code></pre>
  
  <p>I get:</p>
  
  <pre><code>Running virtualenv with interpreter /usr/local/bin/python3
  Using base prefix '/usr/local/Cellar/python3/3.4.0_1/Frameworks/Python.framework/Versions/3.4'
  New python executable in test/bin/python3.4
  Also creating executable in test/bin/python
  Failed to import the site module
  Traceback (most recent call last):
    File "/Users/user/Documents/workspace/test/test/bin/../lib/python3.4/site.py", line 67, in &lt;module&gt;
      import os
    File "/Users/user/Documents/workspace/test/test/bin/../lib/python3.4/os.py", line 634, in &lt;module&gt;
      from _collections_abc import MutableMapping
  ImportError: No module named '_collections_abc'
  ERROR: The executable test/bin/python3.4 is not functioning
  ERROR: It thinks sys.prefix is '/Users/user/Documents/workspace/test' (should be '/Users/user/Documents/workspace/test/test')
  ERROR: virtualenv is not compatible with this system or executable
  </code></pre>