code: def set_date_range(self, start=None, end=None):
          
          start = self._start if start is None else pd.to_datetime(start)
          end = self._end if end is None else pd.to_datetime(end)
          self._update(self._prices.loc[start:end])
docs: Update date range of stats, charts, etc. If None then
          the original date range is used. So to reset to the original
          range, just call with no args.
  
          Args:
              * start (date): start date
              * end (end): end date