code: def _clear_pattern(self):
          
          # pattern group
          self.__interval = None
          self.__days_of_week = set()
          self.__first_day_of_week = None
          self.__day_of_month = None
          self.__month = None
          self.__index = 'first'
          # range group
          self.__start_date = None
          self.__end_date = None
          self.__occurrences = None
docs: Clears this event recurrence