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

def nowrange_(self, col, timeframe):
        """
        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
        """
        df = self._nowrange(col, timeframe)
        if df is None:
            self.err("Can not select range data from now")
            return
        return self._duplicate_(df)