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

def ylabel(self, labels):
        """
        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
        """
        if self.panel_scales_y[0].name is not None:
            return self.panel_scales_y[0].name
        else:
            return labels.get('y', '')