French social security number validation

ssn_fr.py

from collections import namedtuple

FrenchSSNTuple = namedtuple('FrenchSSNTuple', [
    'sex',
    'year',
    'month',
    'departement',
    'city',
    'country',
    'id_month_city',
    'control_key',
])

def split_SSN(ssn):
    """
        Split a French SSN into its parts, according to the rules described on:
        https://fr.wikipedia.org/wiki/Num%C3%A9ro_de_s%C3%A9curit%C3%A9_sociale_en_France#Signification_des_chiffres_du_NIR
        
        The order in which fields are returned allows to use ''.join(*t) to get 
        the SSN back.
        
    """
    assert len(ssn) == 15
    ssb = ssn.lower()
    sex = ssn[:1]
    year = ssn[1:3]
    month = ssn[3:5]
    location = ssn[5:10]
    id_month_city = ssn[10:13]
    control_key = ssn[13:]
    
    dpt = location[:2]
    if dpt.isdigit() and 1 <= int(dpt) <= 95 or dpt in ('2a', '2b'):
        departement = location[:2]
        city = location[2:]
        country = ''
    
    elif dpt.isdigit() and 97 <= int(dpt) <= 98:
        departement = location[:3]
        city = location[3:]
        country = ''
    
    elif dpt == '99':
        departement = '99'
        city = ''
        country = location[2:]
    
    else:
        raise ValueError('Invalid location for SSN: %s' % location)
    
    return (sex, year, month, departement, city, country, id_month_city, control_key)


class FrenchSSN(FrenchSSNTuple):
    @classmethod
    def fromstring(cls, ssn):
        splitted = split_SSN(ssn)
        return cls(*splitted)
    
    def __str__(self):
        return ''.join(self)
    
    @property
    def valid(self):
        return all(
            getattr(self, '_validate_%s' % field, lambda: True)()
            for field in self._fields
        )
    
    def _validate_sex(self):
        return len(self.sex) == 1 and self.sex in '123'
    
    def _validate_year(self):
        return len(self.year) == 2 and self.year.isdigit()
    
    def _validate_month(self):
        try:
            month = int(self.month)
        except ValueError:
            return False
        
        return (
            ( 1 <= month <= 12) or
            (20 <= month <= 42) or
            (50 <= month <= 99)
        )
    
    def _validate_departement(self):
        try:
            dpt = int(self.departement)
        except ValueError:
            return dpt in ('2a', '2b') # Corsica
        return (
            (1 <= dpt <= 95) or # France (mainland)
            (970 < dpt <= 989) or # France (outre-mer)
            (dpt == 99) # abroad
        )
    
    def _validate_city(self):
        return True # TODO
    
    def _validate_country(self):
        return True # TODO
    
    def _validate_id_month_city(self):
        try:
            id_month_city = int(self.id_month_city)
        except ValueError:
            return False
        return 1 <= id_month_city <= 999
    
    def _validate_control_key(self):
        ssn_without_key = self._replace(
            departement={'2a': '19', '2b': 18}.get(self.departement, self.departement),
            control_key=''
        )
        try:
            ssn_without_key = int(''.join(ssn_without_key))
            key = int(self.control_key)
        except ValueError:
            return False
        return key == (97 - ssn_without_key % 97)