Create your first isolated Python environment

# Install virtualenv for Python 2.7 and create a sandbox called my27project:
pip2.7 install virtualenv
virtualenv-2.7 my27project
 
# Use the built-in pyvenv program in Python 3.3 to create a sandbox called my33project:
pyvenv-3.3 my33project
 
# Check the system Python interpreter version:
python --version
# This will show Python 2.6.6
 
# Activate the my27project sandbox and check the version of the default Python interpreter in it:
source my27project/bin/activate
python --version
# This will show Python 2.7.6
deactivate
 
# Activate the my33project sandbox and check the version of the default Python interpreter in it:
source my33project/bin/activate
python --version
# This will show Python 3.3.5
deactivate

When you use virtualenv to create a sandbox it will automatically install setuptools and pip for you inside the sandbox. If you use pyvenv then you must do it yourself. You can reuse the ez_setup.py file you downloaded earlier and just run it after you activate your new sandbox.