def _days_before_month(year, month):
    if not 1 <= month <= 12:
        raise ValueError('month must be in 1..12', month)
    return _DAYS_BEFORE_MONTH[month] + (month > 2 and _is_leap(year))
year, month -> number of days in year preceeding first day of month.
dataset/ETHPy150Open azoft-dev-team/imagrium/env/Lib/datetime.py/_days_before_month