code: def nowrange_(self, col, timeframe):
          
          df = self._nowrange(col, timeframe)
          if df is None:
              self.err("Can not select range data from now")
              return
          return self._duplicate_(df)
docs: Returns a Dataswim instance with rows within a date range from now
          ex: ds.nowrange("Date", "3D") for a 3 days range. Units are: S,
          H, D, W, M, Y