code: def get_value(self, variable = None, table = None):
          
          assert variable is not None, "A variable is needed"
          if table not in self.tables:
              log.error("Table {} is not found in survey tables".format(table))
          df = self.get_values([variable], table)
          return df
docs: Get value
  
          Parameters
          ----------
          variable : string
                    name of the variable
          table : string, default None
                  name of the table hosting the variable
          Returns
          -------
          df : DataFrame, default None
               A DataFrame containing the variable