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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def sum_(self, col: str) -> float: """ Returns the sum of all values in a column :param col: column name :type col: str :return: sum of all the column values :rtype: float :example: ``sum = ds.sum_("Col 1")`` """

        try:
            df = self.df[col]
            num = float(df.sum())
            return num
        except Exception as e:
            self.err(e, "Can not sum data on column " + str(col))