code: def sum_(self, col: str) -> float:
          
          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))
docs: 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")``