def reset(self, name):
        """Reset assigned value for field.

        Resetting a field will return it to its default value or None.

        Args:
          name: Name of field to reset.
        """
        message_type = type(self)
        try:
            field = message_type.field_by_name(name)
        except KeyError:
            if name not in message_type.__by_name:
                raise AttributeError('Message %s has no field %s' % (
                    message_type.__name__, name))
        if field.repeated:
            self.__tags[field.number] = FieldList(field, [])
        else:
            self.__tags.pop(field.number, None)