virtualenv is a tool that creates “new” Python installations that are copies of your installed Python. These “virtual environments” are clean and consistent.
To keep work areas clean and consistent, and minimize assumptions about what tools are installed where. This makes it easier to have repeatable, consistent builds.
$ pip install virtualenv
# assume you have created a directory D and moved to it!
$ virtualenv --no-site-packages testenv
$ . testenv/bin/activate # windows -> . testenv\Scripts\activate.bat
# your prompt should change to say (testenv)
$ deactivate
# remove the testenv directory
rm -rf testenv