virtualenv_activate ()
{
    local virtualenv_dir="$HOME/work/virtualenv"
    if [ $# -ne 1 ]; then
       echo "
Usage:
    virtualenv_activate <env_dir>
"
        return 1
    fi

    local activate_script="$virtualenv_dir/$1/bin/activate"
    if [ ! -f "$activate_script" ]; then
        echo "Invalid environment: $1"
        return 1
    fi

    . $activate_script
    return 0
}