Finnish personal identity code (henkilötunnus/hetu) generator in Python

hetu.py

"""
MIT License

Copyright (c) 2023 Olli Paloviita

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
"""
import datetime
from calendar import monthrange
from typing import Iterator


def hetus(
    future_hetus: bool = False,
    temporary_hetus: bool = False,
    rare_hetus: bool = True,
) -> Iterator[str]:
    """Finnish personal identity code (henkilötunnus/hetu) generator

    Yields Finnish personal identity codes one by one, starting from the most common
    century symbols (-A+) and then the new century symbols introduced in 2023
    (BCDEFYXVWU). Finnish personal identity codes are functionally very similar to
    social security numbers. More info: https://fi.wikipedia.org/wiki/Henkil%C3%B6tunnus

    Args:
        future_hetus: Include future hetus that no one can have yet
        temporary_hetus: Include temporary hetus with numbers 900-999
        rare_hetus: Include hetus with rare century symbols (BCDEFYXVWU)

    Returns:
        Personal identity code string iterator
    """

    years_since_2000 = datetime.date.today().year - 2000

    def century_symbol_to_number(century_symbol):
        if century_symbol in "+":
            return 1800
        elif century_symbol in "-YXWVU":
            return 1900
        elif century_symbol in "ABCDEF":
            return 2000

    def years_in_century(century_symbol):
        return (
            years_since_2000 + 1
            if not future_hetus and century_symbol_to_number(century_symbol) == 2000
            else 100
        )

    def days_in_month(century_symbol, year_short, month):
        year = century_symbol_to_number(century_symbol) + year_short
        return monthrange(year, month)[1]

    for century_symbol in "-A+BCDEFYXVWU" if rare_hetus else "-A+":
        for year_short in range(0, years_in_century(century_symbol)):
            for month in range(1, 12 + 1):
                for day in range(1, days_in_month(century_symbol, year_short, month) + 1):
                    date = f"{day:02}{month:02}{year_short:02}"
                    for num in range(2, 1000 if temporary_hetus else 900):
                        check = "0123456789ABCDEFHJKLMNPRSTUVWXY"[int(f"{date}{num:03}") % 31]
                        yield f"{date}{century_symbol}{num:03}{check}"


if __name__ == "__main__":
    # print 276000000+ hetus
    for hetu in hetus():
        print(hetu)