Return True if it's an holiday.
        In addition to the regular holidays, you can add exceptions.

        By providing ``extra_holidays``, you'll state that these dates **are**
        holidays, even if not in the regular calendar holidays (or weekends).

def is_holiday(self, day, extra_holidays=None):
        """Return True if it's an holiday.
        In addition to the regular holidays, you can add exceptions.

        By providing ``extra_holidays``, you'll state that these dates **are**
        holidays, even if not in the regular calendar holidays (or weekends).

        """
        day = cleaned_date(day)

        if extra_holidays:
            extra_holidays = tuple(map(cleaned_date, extra_holidays))

        if extra_holidays and day in extra_holidays:
            return True

        return day in self.holidays_set(day.year)