def add_chart(self, sheetname, x_col, y_col):
ws = self.wb[sheetname]
xtitle = ws.cell(1, x_col).value
ytitle = ws.cell(1, y_col).value
chart = LineChart()
chart.title = "%s - %s" % (ytitle, xtitle)
chart.style = 13
chart.x_axis.title = xtitle
chart.y_axis.title = ytitle
chart.marker = True
chart.smooth = True
y_data = Reference(ws, min_col=y_col, min_row=1, max_col=y_col, max_row=self.current_row)
chart.add_data(y_data, titles_from_data=True)
x_data = Reference(ws, min_col=x_col, min_row=2, max_col=x_col, max_row=self.current_row)
chart.set_categories(x_data)
s0 = chart.series[0]
s0.marker.symbol = "circle"
s0.smooth = True
if 0 == self.chart_row:
self.chart_row = self.current_row
ws.add_chart(chart, "A%d" % self.chart_row)
# row height is 7.5/16 cm by default
self.chart_row = self.chart_row + chart.height / 7.5 * 16 + 2
