Delete data fields from this struct instance

def del_fields(self, *names):
        """Delete data fields from this struct instance"""
        cls = type(self)
        self.__class__ = cls
        for n in names:
            # don't raise error if a field is absent
            if isinstance(getattr(cls, n, None), DataField):
                if n in self._field_values:
                    del self._field_values[n]
                delattr(cls, n)