code: def _build_multipart(cls, data):
          
          boundary = b'--------------GHSKFJDLGDS7543FJKLFHRE75642756743254'
          sep_boundary = b'\n--' + boundary
          end_boundary = sep_boundary + b'--'
          end_items = end_boundary, b"\n",
          builder = functools.partial(
              cls._build_part,
              sep_boundary=sep_boundary,
          )
          part_groups = map(builder, data.items())
          parts = itertools.chain.from_iterable(part_groups)
          body_items = itertools.chain(parts, end_items)
          content_type = 'multipart/form-data; boundary=%s' % boundary.decode('ascii')
          return b''.join(body_items), content_type
docs: Build up the MIME payload for the POST data