from: Stackoverflow Use different Python version with virtualenv
(1) Locate your python
which python3
/Library/Frameworks/Python.framework/Versions/3.4/bin/python3
(2) Make your virtualenv (via virtualenvwrapper)
mkvirtualenv -p /Library/Frameworks/Python.framework/Versions/3.4/bin/python3 [virtualenv name]
Even if your default is python 2.7+, invoking the virtualenv will default to python 3+
