docs: def __validInterval(self, start, finish):
          """Check if the interval is correct.
  
          An interval is correct if it has less than 1001
          users. If the interval is correct, it will be added
          to '_intervals' attribute. Else, interval will be
          split in two news intervals and these intervals
          will be checked.
  
          :param start: start date of the interval.
          :type start: datetime.date.
          :param finish: finish date of the interval.
          :type finish: datetime.date.
          """
          url = self.__getURL(1,
                              start.strftime("%Y-%m-%d"),
                              finish.strftime("%Y-%m-%d"))
  
          data = self.__readAPI(url)
  
          if data["total_count"] >= 1000:
              middle = start + (finish - start)/2
              self.__validInterval(start, middle)
              self.__validInterval(middle, finish)
          else:
              self.__intervals.append([start.strftime("%Y-%m-%d"),
                                       finish.strftime("%Y-%m-%d")])
              self.__logger.info("New valid interval: " +
                                 start.strftime("%Y-%m-%d") +
                                 " to " +
                                 finish.strftime("%Y-%m-%d"))