ohmyzsh/plugins/virtualenv/virtualenv.plugin.zsh

function virtualenv_prompt_info(){
  if [[ -n $VIRTUAL_ENV ]]; then
    printf "%s[%s] " "%{${fg[yellow]}%}" ${${VIRTUAL_ENV}:t}
  fi
}

# disables prompt mangling in virtual_env/bin/activate
export VIRTUAL_ENV_DISABLE_PROMPT=1