code: def rewind_body(prepared_request):
      
      body_seek = getattr(prepared_request.body, 'seek', None)
      if body_seek is not None and isinstance(prepared_request._body_position, integer_types):
          try:
              body_seek(prepared_request._body_position)
          except (IOError, OSError):
              raise UnrewindableBodyError("An error occurred when rewinding request "
                                          "body for redirect.")
      else:
          raise UnrewindableBodyError("Unable to rewind request body for redirect.")
docs: Move file pointer back to its recorded starting position
      so it can be read again on redirect.