XML bug when using dataLabels.numFmt
*Created originally on Bitbucket by [liuyuqian](https://bitbucket.org/%7B987af662-7ddf-415a-b86c-03da3f6cb95f%7D/)* I'm tring to change the format of datalabel in barcharts.Generated xlsx file will raise a XML error when change dataLabels.numFmt. I unziped a right xlsx file,the "numFmt" label is: ``` #!xml <c:numFmt formatCode="0%" sourceLinked="0"/> ``` and the "numFmt" label in generated xlsx is: ``` #!xml <numFmt val="0%"/><showVal val="1"/> ``` Demo codes: ``` #!python from openpyxl import Workbook from openpyxl.chart import BarChart, Series, Reference from openpyxl.chart.label import DataLabelList wb = Workbook(write_only=True) ws = wb.create_sheet() rows = [('Number', 'pct'), (2, 0.1), (3, 0.2), (4, 0.1), (5, 0.2), (6, 0.3), (7, 0.1)] for row in rows: ws.append(row) chart1 = BarChart() chart1.type = "col" chart1.style = 10 data = Reference(ws, min_col=2, min_row=1, max_row=7, max_col=3) cats = Reference(ws, min_col=1, min_row=2, max_row=7) chart1.add_data(data, titles_from_data=True) chart1.set_categories(cats) chart1.dataLabels = DataLabelList() chart1.dataLabels.showVal=True chart1.dataLabels.numFmt='0.0%' ws.add_chart(chart1, "A10") wb.save("bar_datalabel.xlsx") ```
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