ohmyzsh/plugins/virtualenv/virtualenv.plugin.zsh

function virtualenv_prompt_info(){
  [[ -n ${VIRTUAL_ENV} ]] || return
  echo "${ZSH_THEME_VIRTUALENV_PREFIX=[}${VIRTUAL_ENV:t:gs/%/%%}${ZSH_THEME_VIRTUALENV_SUFFIX=]}"
}

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