code: def ylabel(self, labels):
          
          if self.panel_scales_y[0].name is not None:
              return self.panel_scales_y[0].name
          else:
              return labels.get('y', '')
docs: Determine x-axis label
  
          Parameters
          ----------
          labels : dict
              Labels as specified by the user through the ``labs`` or
              ``ylab`` calls.
  
          Returns
          -------
          out : str
              y-axis label