code: def _validate_arguments(self):
          
          super(FactorTerm, self)._validate_arguments()
          if self.coding not in self._encodings:
              raise ValueError("coding must be one of {}, "\
                               "but found: {}".format(self._encodings, self.coding))
  
          return self
docs: method to sanitize model parameters
  
          Parameters
          ---------
          None
  
          Returns
          -------
          None