pesel.py

from datetime import date

class PESEL(object):
    """Parses PESEL number, checks validity and extracts gender + DOB data."""
    gender = None
    birth_date = None
    pesel = None

    def __init__(self, pesel):
        try:
            int(pesel)
        except ValueError:
            raise ValueError("PESEL must contain only digits.")
        if len(pesel) != 11:
            raise ValueError("PESEL must have exactly 11 digits.")
        muls = (1,3,7,9,1,3,7,9,1,3,1)
        chksum = 0
        for i in range(11):
            chksum += int(pesel[i]) * muls[i]
        if chksum % 10 % 10 != 0:
            raise ValueError("Invalid checksum.")
        y = int(pesel[:2])
        m = int(pesel[2:4])
        d = int(pesel[4:6])
        m2century = {80: 1800, 0: 1900, 20: 2000, 40: 2100, 60: 2200}
        for md, cent in m2century.items():
            if 1 <= m - md <= 12:
                y += cent
                m -= md
                break
        try:
            self.birth_date = date(y,m,d)
        except ValueError:
            raise ValueError("PESEL contains invalid birth date.")
        self.gender = 'm' if int(pesel[9]) % 10 else 'f'
        self.pesel = pesel