code: def set_axis_labels(self, x_var=None, y_var=None):
          
          if x_var is not None:
              if x_var in self.data.coords:
                  self._x_var = x_var
                  self.set_xlabels(label_from_attrs(self.data[x_var]))
              else:
                  # x_var is a string
                  self.set_xlabels(x_var)
  
          if y_var is not None:
              if y_var in self.data.coords:
                  self._y_var = y_var
                  self.set_ylabels(label_from_attrs(self.data[y_var]))
              else:
                  self.set_ylabels(y_var)
          return self
docs: Set axis labels on the left column and bottom row of the grid.