docs: def normalize(body_part_tup,):
      """Normalize a tuple of BodyPart objects to a string.
  
      Normalization is done by sorting the body_parts by the Content- Disposition headers,
      which is typically on the form, ``form-data; name="name_of_part``.
  
      """
      return '\n\n'.join(
          [
              '{}\n\n{}'.format(
                  str(p.headers[b'Content-Disposition'], p.encoding), p.text
              )
              for p in sorted(
                  body_part_tup, key=lambda p: p.headers[b'Content-Disposition']
              )
          ]
      )