str: Subtype Group ID

def subtype_group_id(self):
        """
        str: Subtype Group ID
        """
        self._validate()
        self._validate_for_subtype_group_id()

        parts = []
        parts.append(self.election_type)
        parts.append(self.subtype)
        parts.append(self.date)
        return ".".join(parts)