Using Python 3 in virtualenv

Using virtualenv, I run my projects with the default version of Python (2.7). On one project, I need to use Python 3.4.

I used brew install python3 to install it on my Mac. Now, how do I create a virtualenv that uses the new version?

e.g. sudo virtualenv envPython3

If I try:

    virtualenv -p python3 test

I get:

    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 <module>
        import os
      File "/Users/user/Documents/workspace/test/test/bin/../lib/python3.4/os.py", line 634, in <module>
        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

simply run

    virtualenv -p python3 envname

Update after OP's edit:

There was a bug in the OP's version of virtualenv, as described here. The problem was fixed by running:

    pip install --upgrade virtualenv

From: stackoverflow.com/q/23842713