Create a new Virtualenv
virtualenv {name_of_virtualenv}
Interactively load the virtualenv
source ./{name_of_virtualenv}/bin/activate
Work in the virtualenv
cd ~/{name_of_virtualenv}
git clone {repo}
pip install -r ./{repo}/requirements.txt
./{repo}/{some_thing}.py
Or, to run a python script within a virtualenv once (e.g. scheduled via cron)
./{name_of_virtualenv}/bin/python2.7 ./{name_of_virtualenv}/{repo}/{some_thing}.py