Returns the century code for a given year

def _get_century_code(year):
        """Returns the century code for a given year"""
        if 2000 <= year < 3000:
            separator = 'A'
        elif 1900 <= year < 2000:
            separator = '-'
        elif 1800 <= year < 1900:
            separator = '+'
        else:
            raise ValueError('Finnish SSN do not support people born before the year 1800 or after the year 2999')
        return separator