Return x & y scales for panel i

        Parameters
        ----------
        i : int
          Panel id

        Returns
        -------
        scales : types.SimpleNamespace
          Class attributes *x* for the x scale and *y*
          for the y scale of the panel

def get_scales(self, i):
        """
        Return x & y scales for panel i

        Parameters
        ----------
        i : int
          Panel id

        Returns
        -------
        scales : types.SimpleNamespace
          Class attributes *x* for the x scale and *y*
          for the y scale of the panel

        """
        # wrapping with np.asarray prevents an exception
        # on some datasets
        bool_idx = (np.asarray(self.layout['PANEL']) == i)
        xsc = None
        ysc = None

        if self.panel_scales_x:
            idx = self.layout.loc[bool_idx, 'SCALE_X'].values[0]
            xsc = self.panel_scales_x[idx-1]

        if self.panel_scales_y:
            idx = self.layout.loc[bool_idx, 'SCALE_Y'].values[0]
            ysc = self.panel_scales_y[idx-1]

        return types.SimpleNamespace(x=xsc, y=ysc)