code: def _render_parts(self, header_parts):
          
          parts = []
          iterable = header_parts
          if isinstance(header_parts, dict):
              iterable = header_parts.items()
  
          for name, value in iterable:
              if value is not None:
                  parts.append(self._render_part(name, value))
  
          return '; '.join(parts)
docs: Helper function to format and quote a single header.
  
          Useful for single headers that are composed of multiple items. E.g.,
          'Content-Disposition' fields.
  
          :param header_parts:
              A sequence of (k, v) tuples or a :class:`dict` of (k, v) to format
              as `k1="v1"; k2="v2"; ...`.