code: def _sline_bokeh(self, window_size, y_label):
          
          try:
              ds2 = self.clone_()
              window = np.ones(int(window_size)) / float(window_size)
              ds2.df[y_label] = np.convolve(self.df[self.y], window, 'same')
              ds2.chart(self.x, y_label)
              return ds2.line_()
          except Exception as e:
              self.err(e, self._sline_bokeh, "Can not draw smooth line chart")
docs: Returns a chart with a smooth line from a serie