A datetime.datetime object of when the certificate is last to be
        considered valid.

def end_date(self, value):
        """
        A datetime.datetime object of when the certificate is last to be
        considered valid.
        """

        if not isinstance(value, datetime):
            raise TypeError(_pretty_message(
                '''
                end_date must be an instance of datetime.datetime, not %s
                ''',
                _type_name(value)
            ))

        self._end_date = value