code: def save_binary(self, fname, silent=True):
          
          _check_call(_LIB.XGDMatrixSaveBinary(self.handle,
                                               c_str(fname),
                                               ctypes.c_int(silent)))
docs: Save DMatrix to an XGBoost buffer.  Saved binary can be later loaded
          by providing the path to :py:func:`xgboost.DMatrix` as input.
  
          Parameters
          ----------
          fname : string
              Name of the output buffer file.
          silent : bool (optional; default: True)
              If set, the output is suppressed.