The formatting template string that determines how a number in this
        series is formatted, both in the chart and in the Excel spreadsheet;
        for example '#,##0.0'. If not specified for this series, it is
        inherited from the parent chart data object.

def number_format(self):
        """
        The formatting template string that determines how a number in this
        series is formatted, both in the chart and in the Excel spreadsheet;
        for example '#,##0.0'. If not specified for this series, it is
        inherited from the parent chart data object.
        """
        number_format = self._number_format
        if number_format is None:
            return self._chart_data.number_format
        return number_format