docs: def download_virtualenv(version, dldir=None):
      '''
      Download virtualenv package from pypi and return response that can be
      read and written to file
  
      :param str version: version to download or latest version if None
      :param str dldir: directory to download into or None for cwd
      '''
      dl_url = PYPI_DL_URL.format(VER=version)
      filename = basename(dl_url)
      if dldir:
          dl_path = join(dldir, filename)
      else:
          dl_path = filename
      data = urlopen(PYPI_DL_URL.format(VER=version))
      with open(dl_path, 'wb') as fh:
          fh.write(data.read())
      return dl_path