_workon() {
    local cur prev envs
    COMPREPLY=()
    cur="${COMP_WORDS[COMP_CWORD]}"
    prev="${COMP_WORDS[COMP_CWORD-1]}"
    envs=$(ls /opt/pythonenv/)

    COMPREPLY=( $(compgen -W "${envs}" -- ${cur}) )
}

complete -F _workon workon