Add Late Summer holiday (First Monday of September)

def get_variable_days(self, year):
        """
        Add Late Summer holiday (First Monday of September)
        """
        days = super(LateSummer, self).get_variable_days(year)
        days.append((
            self.get_nth_weekday_in_month(year, 9, MON),
            "Late Summer Holiday"
        ))
        return days