Preventing global package install with PIPREQUIREVIRTUALENV

To make sure you have an virtual env activated whenever you do pip install, add the following line to your .bashrc

export PIP_REQUIRE_VIRTUALENV=true

If you now try to install packages outside a virtual environment pip will remind you.

$ pip install django
ERROR: Could not find an activated virtualenv (required).

In some cases you will need to install global packages (like vim plugins etc). For that create a separate bash function like this

gpip() {
    PIP_REQUIRE_VIRTUALENV=false pip "$@"
}