Virtualenv Auto-activate

.virtualenvhelper

cd ()
{
    builtin cd "$@"
    RETVAL=$?
    
    # Test for successful real cd:
    if [ 0 -ne $RETVAL ]; then
        return $RETVAL
    fi
    
    # Deactivate once I move outside the virtualenv directory or 
    # do nothing when I'm still in this same virtualenv directory
    # (Assuming no one nests virtualenvs....)
    if [ ! -z "$VIRTUAL_ENV" ]; then
        if [ "$PWD" = "${PWD#$VIRTUAL_ENV}" ]; then
            deactivate
            echo
            echo "Deactivating virtualenv..."
        else
            return 0
        fi
    fi
    
    # "Detect" virtualenv files:
    if [ -r "ve/bin/activate" ]; then
        if head -n 1 "ve/bin/activate" | grep -q 'source bin/activate' > /dev/null; then
            source "ve/bin/activate"
            echo
            echo "Activating virtualenv..."
        fi
    fi
    return 0
}