code: def validateInterval(self, startTime, endTime):
      
      start = int(startTime)
      end = int(endTime)
      if start > end:
        raise Exception("starttime is greater than endtime.")
docs: Helper function to validate interval.
      An interval is valid if starttime and endtime are integrals,
      and starttime is less than the endtime.
      Raises exception if interval is not valid.