code: def save(self, obj, data, is_m2m=False):
          
          if not self.readonly:
              attrs = self.attribute.split('__')
              for attr in attrs[:-1]:
                  obj = getattr(obj, attr, None)
              cleaned = self.clean(data)
              if cleaned is not None or self.saves_null_values:
                  if not is_m2m:
                      setattr(obj, attrs[-1], cleaned)
                  else:
                      getattr(obj, attrs[-1]).set(cleaned)
docs: If this field is not declared readonly, the object's attribute will
          be set to the value returned by :meth:`~import_export.fields.Field.clean`.