code: def set_r_df(self, value):
          ''' setter '''
          if isinstance(value, pd.DataFrame) is False and self.__r_df is not None:
              raise TypeError("The type of `__r_df` must be `pd.DataFrame`.")
          self.__r_df = valuf set_r_df(self, value):
          ''' setter '''
          if isinstance(value, pd.DataFrame) is False and self.__r_df is not None:
              raise TypeError("The type of `__r_df` must be `pd.DataFrame`.")
          self.__r_df = value
docs: setter