Remember to switch the default cython, ipython, pep8, python, sphinx, and virtualenv ports (MacPorts).

port_select_python.sh

# Select python version
port select --list python
port select --set python python33

# Select cython version
port select --list cython
port select --set cython cython33

# Select ipython version
port select --list ipython
port select --set ipython ipython33

# Select pep8 version
port select --list pep8
port select --set pep8 pep833

# Select sphinx version
port select --list sphinx
port select --set sphinx py33-sphinx

# Select virtualenv version
port select --list virtualenv
port select --set virtualenv virtualenv33