brew install pyenv # Mac OS X
curl -L <pyenv_installer_url> | bash # Linux
$ cd /path/to/project
$ pyenv install 3.4.1
$ pyenv local 3.4.1
$ python --version
Python 3.4.1
$ which python
/home/playpauseandstop/.pyenv/shims/python
$ cd ..
$ python --version
Python 2.7.8