decode/unmarshal Ruby Date in python

unmarshal-ruby-date.py

from datetime import date, timedelta
from rubymarshal.classes import UsrMarshal
from rubymarshal.reader import loads
data = b'\x04\x08U:\tDate[\x0bi\x00i\x03\xe5R%i\x00i\x00i\x00f\x0c2299161'
# 1984-12-18
data = loads(data)
if isinstance(data, UsrMarshal):
  # data._private_data[1]  is days since Julian Day (November 24, 4714 BC)
  data = (date(1900, 1, 1) + timedelta(days=data._private_data[1] - 2415021)).strftime('%Y-%m-%d')

print(str(data))