def _data(self):
        """A deep copy NDArray of the data array associated with the BaseSparseNDArray.

        This function blocks. Do not use it in performance critical code.
        """
        self.wait_to_read()
        hdl = NDArrayHandle()
        check_call(_LIB.MXNDArrayGetDataNDArray(self.handle, ctypes.byref(hdl)))
        return NDArray(hdl)