docs: def get_valid_filename(s):
      """
      Returns the given string converted to a string that can be used for a clean
      filename. Specifically, leading and trailing spaces are removed; other
      spaces are converted to underscores; and anything that is not a unicode
      alphanumeric, dash, underscore, or dot, is removed.
      >>> get_valid_filename("john's portrait in 2004.jpg")
      'johns_portrait_in_2004.jpg'
      """
      s = s.strip().replace(" ", "_")
      return re.sub(r"(?u)[^-\w.]", "", s)