Return the member of :ref:`XlChartType` that corresponds to the chart
        type of *plot*.

def chart_type(cls, plot):
        """
        Return the member of :ref:`XlChartType` that corresponds to the chart
        type of *plot*.
        """
        try:
            chart_type_method = {
                'AreaPlot':     cls._differentiate_area_chart_type,
                'Area3DPlot':   cls._differentiate_area_3d_chart_type,
                'BarPlot':      cls._differentiate_bar_chart_type,
                'BubblePlot':   cls._differentiate_bubble_chart_type,
                'DoughnutPlot': cls._differentiate_doughnut_chart_type,
                'LinePlot':     cls._differentiate_line_chart_type,
                'PiePlot':      cls._differentiate_pie_chart_type,
                'RadarPlot':    cls._differentiate_radar_chart_type,
                'XyPlot':       cls._differentiate_xy_chart_type,
            }[plot.__class__.__name__]
        except KeyError:
            raise NotImplementedError(
                "chart_type() not implemented for %s" %
                plot.__class__.__name__
            )
        return chart_type_method(plot)