Product features · Holiday-aware working-day shifts

from datetime import date, timedelta

def working_day_shift(start, days, holidays):
    if type(start) is not date or type(days) is not int or not -366 <= days <= 366:
        raise ValueError("days.input")
    if type(holidays) is not set or len(holidays) > 1000 or any(type(d) is not date for d in holidays):
        raise ValueError("days.holidays")
    remaining, step = abs(days), 1 if days >= 0 else -1
    for _ in range(7*(remaining+len(holidays))+7):
        if remaining == 0:
            return start
        try:
            start += timedelta(days=step)
        except OverflowError as error:
            raise ValueError("days.range") from error
        if start.weekday() < 5 and start not in holidays:
            remaining -= 1
    raise RuntimeError("days.steps")