docs: def download_setuptools(version=DEFAULT_VERSION, download_base=DEFAULT_URL,
                          to_dir=os.curdir, delay=15,
                          downloader_factory=get_best_downloader):
      """Download setuptools from a specified location and return its filename
  
      `version` should be a valid setuptools version number that is available
      as an egg for download under the `download_base` URL (which should end
      with a '/'). `to_dir` is the directory where the egg will be downloaded.
      `delay` is the number of seconds to pause before an actual download
      attempt.
  
      ``downloader_factory`` should be a function taking no arguments and
      returning a function for downloading a URL to a target.
      """
      # making sure we use the absolute path
      to_dir = os.path.abspath(to_dir)
      tgz_name = "setuptools-%s.tar.gz" % version
      url = download_base + tgz_name
      saveto = os.path.join(to_dir, tgz_name)
      if not os.path.exists(saveto):  # Avoid repeated downloads
          log.warn("Downloading %s", url)
          downloader = downloader_factory()
          downloader(url, saveto)
      return os.path.realpath(saveto)