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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def num_row(self):
 """Get the number of rows in the DMatrix. Returns ------- number of rows : int """

        ret = ctypes.c_ulong()
        _check_call(_LIB.XGDMatrixNumRow(self.handle,
                                         ctypes.byref(ret)))
        return ret.value