code: def frequency(self):
          
          freqOptions = ("YEARLY", "MONTHLY", "WEEKLY", "DAILY")
          if self.rule._freq < len(freqOptions):
              return freqOptions[self.rule._freq]
          else:
              return "unsupported_frequency_{}".format(self.rule._freq)
docs: How often the recurrence repeats.
          ("YEARLY", "MONTHLY", "WEEKLY", "DAILY")