str: Ballot ID

def ballot_id(self):
        """
        str: Ballot ID
        """
        self._validate()
        self._validate_division(self.division)
        self._validate_for_ballot_id()

        parts = []
        parts.append(self.election_type)
        if self.subtype:
            parts.append(self.subtype)
        if self.organisation:
            parts.append(self.organisation)
        if self.division:
            parts.append(self.division)
        if self.contest_type:
            parts.append(self.contest_type)
        parts.append(self.date)
        return ".".join(parts)