views.py 文件源码

def _calculate_value(self, calculation, values):
        """
        Parse and perform a calculation using a dict of fields

        Using either a dict of values to field names

        Returns a NaN if the calculation cannot be performed, e.g.
        incorrect field names.
        """
        nsp = NumericStringParser()
        field_regex = r'\{(.+?)\}'
        interpolated_calculation = re.sub(field_regex, self._replace_fields(values), calculation)
        try:
            result = nsp.eval(interpolated_calculation)
        except ParseException:
            return None
        return result