code: def rename(self, data, variables=None):
          
          if variables is None:
              variables = self.variables
          return data.rename(columns={y: x for x, y in variables.items()})
docs: Renames the columns according the variable mapping.
  
          Parameters
          ----------
          data: DataFrame
          variables: None or dict, default None
              If None, uses self.variables
  
          Returns
          -------
          data: DataFrame
              Renamed data.