code: def num_data(self):
          
          if self.handle is not None:
              ret = ctypes.c_int()
              _safe_call(_LIB.LGBM_DatasetGetNumData(self.handle,
                                                     ctypes.byref(ret)))
              return ret.value
          else:
              raise LightGBMError("Cannot get num_data before construct dataset")
docs: Get the number of rows in the Dataset.
  
          Returns
          -------
          number_of_rows : int
              The number of rows in the Dataset.